Final batch for "merge -sort" optimization.
* en/ort-perf-batch-15:
merge-ort: remove compile-time ability to turn off usage of memory pools
merge-ort: reuse path strings in pool_alloc_filespec
merge-ort: store filepairs and filespecs in our mem_pool
diffcore-rename, merge-ort: add wrapper functions for filepair alloc/dealloc
merge-ort: switch our strmaps over to using memory pools
merge-ort: set up a memory pool
merge-ort: add pool_alloc, pool_calloc, and pool_strndup wrappers
diffcore-rename: use a mem_pool for exact rename detection's hashmap
merge-ort: rename str{map,intmap,set}_func()
Leak plugging.
* ah/plugleaks:
reset: clear_unpack_trees_porcelain to plug leak
builtin/rebase: fix options.strategy memory lifecycle
builtin/merge: free found_ref when done
builtin/mv: free or UNLEAK multiple pointers at end of cmd_mv
convert: release strbuf to avoid leak
read-cache: call diff_setup_done to avoid leak
ref-filter: also free head for ATOM_HEAD to avoid leak
diffcore-rename: move old_dir/new_dir definition to plug leak
builtin/for-each-repo: remove unnecessary argv copy to plug leak
builtin/submodule--helper: release unused strbuf to avoid leak
environment: move strbuf into block to plug leak
fmt-merge-msg: free newly allocated temporary strings when done
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:
Before After
no-renames: 198.1 ms ± 2.6 ms 198.5 ms ± 3.4 ms
mega-renames: 715.8 ms ± 4.0 ms 679.1 ms ± 5.6 ms
just-one-mega: 276.8 ms ± 4.2 ms 271.9 ms ± 2.8 ms
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We want to be able to allocate filespecs and filepairs using a mem_pool.
However, filespec data will still remain outside the pool (perhaps in
the future we could plumb the pool through the various diff APIs to
allocate the filespec data too, but for now we are limiting the scope).
Add some extra functions to allocate these appropriately based on the
non-NULL-ness of opt->priv->pool, as well as some extra functions to
handle correctly deallocating the relevant parts of them. A future
commit will make use of these new functions.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Exact rename detection, via insert_file_table(), uses a hashmap to store
files by oid. Use a mem_pool for the hashmap entries so these can all be
allocated and deallocated together.
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:
Before After
no-renames: 204.2 ms ± 3.0 ms 202.5 ms ± 3.2 ms
mega-renames: 1.076 s ± 0.015 s 1.072 s ± 0.012 s
just-one-mega: 364.1 ms ± 7.0 ms 357.3 ms ± 3.9 ms
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Documentation on "git diff -l<n>" and diff.renameLimit have been
updated, and the defaults for these limits have been raised.
* en/rename-limits-doc:
rename: bump limit defaults yet again
diffcore-rename: treat a rename_limit of 0 as unlimited
doc: clarify documentation for rename/copy limits
diff: correct warning message when renameLimit exceeded
old_dir/new_dir are free()'d at the end of update_dir_rename_counts,
however if we return early we'll never free those strings. Therefore
we should move all new allocations after the possible early return,
avoiding a leak.
This seems like a fairly recent leak, that started happening since the
early-return was added in:
1ad69eb0dc (diffcore-rename: compute dir_rename_counts in stages, 2021-02-27)
LSAN output from t0022:
Direct leak of 7 byte(s) in 1 object(s) allocated from:
#0 0x486804 in strdup ../projects/compiler-rt/lib/asan/asan_interceptors.cpp:452:3
#1 0xa71e48 in xstrdup wrapper.c:29:14
#2 0x7db9c7 in update_dir_rename_counts diffcore-rename.c:464:12
#3 0x7db6ae in find_renames diffcore-rename.c:1062:3
#4 0x7d76c3 in diffcore_rename_extended diffcore-rename.c:1472:18
#5 0x7b4cfc in diffcore_std diff.c:6705:4
#6 0x855e46 in log_tree_diff_flush log-tree.c:846:2
#7 0x856574 in log_tree_diff log-tree.c:955:3
#8 0x856574 in log_tree_commit log-tree.c:986:10
#9 0x9a9c67 in print_commit_summary sequencer.c:1329:7
#10 0x52e623 in cmd_commit builtin/commit.c:1862:3
#11 0x4ce83e in run_builtin git.c:475:11
#12 0x4ccafe in handle_builtin git.c:729:3
#13 0x4cb01c in run_argv git.c:818:4
#14 0x4cb01c in cmd_main git.c:949:19
#15 0x6b3f3d in main common-main.c:52:11
#16 0x7fe397c7a349 in __libc_start_main (/lib64/libc.so.6+0x24349)
Direct leak of 7 byte(s) in 1 object(s) allocated from:
#0 0x486804 in strdup ../projects/compiler-rt/lib/asan/asan_interceptors.cpp:452:3
#1 0xa71e48 in xstrdup wrapper.c:29:14
#2 0x7db9bc in update_dir_rename_counts diffcore-rename.c:463:12
#3 0x7db6ae in find_renames diffcore-rename.c:1062:3
#4 0x7d76c3 in diffcore_rename_extended diffcore-rename.c:1472:18
#5 0x7b4cfc in diffcore_std diff.c:6705:4
#6 0x855e46 in log_tree_diff_flush log-tree.c:846:2
#7 0x856574 in log_tree_diff log-tree.c:955:3
#8 0x856574 in log_tree_commit log-tree.c:986:10
#9 0x9a9c67 in print_commit_summary sequencer.c:1329:7
#10 0x52e623 in cmd_commit builtin/commit.c:1862:3
#11 0x4ce83e in run_builtin git.c:475:11
#12 0x4ccafe in handle_builtin git.c:729:3
#13 0x4cb01c in run_argv git.c:818:4
#14 0x4cb01c in cmd_main git.c:949:19
#15 0x6b3f3d in main common-main.c:52:11
#16 0x7fe397c7a349 in __libc_start_main (/lib64/libc.so.6+0x24349)
SUMMARY: AddressSanitizer: 14 byte(s) leaked in 2 allocation(s).
Signed-off-by: Andrzej Hunt <andrzej@ahunt.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Performance tweaks of "git merge -sort" around lazy fetching of objects.
* en/ort-perf-batch-13:
merge-ort: add prefetching for content merges
diffcore-rename: use a different prefetch for basename comparisons
diffcore-rename: allow different missing_object_cb functions
t6421: add tests checking for excessive object downloads during merge
promisor-remote: output trace2 statistics for number of objects fetched
More fix-ups and optimization to "merge -sort".
* en/ort-perf-batch-12:
merge-ort: miscellaneous touch-ups
Fix various issues found in comments
diffcore-rename: avoid unnecessary strdup'ing in break_idx
merge-ort: replace string_list_df_name_compare with faster alternative
In commit 89973554b5 (diffcore-rename: make diff-tree -l0 mean
-l<large>, 2017-11-29), -l0 was given a special magical "large" value,
but one which was not large enough for some uses (as can be seen from
commit 9f7e4bfa3b (diff: remove silent clamp of renameLimit,
2017-11-13). Make 0 (or a negative value) be treated as unlimited
instead and update the documentation to mention this.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
merge-ort was designed to minimize the amount of data needed and used,
and several changes were made to diffcore-rename to take advantage of
extra metadata to enable this data minimization (particularly the
relevant_sources variable for skipping "irrelevant" renames). This
effort obviously succeeded in drastically reducing computation times,
but should also theoretically allow partial clones to download much less
information. Previously, though, the "prefetch" command used in
diffcore-rename had never been modified and downloaded many blobs that
were unnecessary for merge-ort. This commit corrects that.
When doing basename comparisons, we want to fetch only the objects that
will be used for basename comparisons. If after basename fetching this
leaves us with no more relevant sources (or no more destinations), then
we won't need to do the full inexact rename detection and can skip
downloading additional source and destination files. Even if we have to
do that later full inexact rename detection, irrelevant sources are
culled after basename matching and before the full inexact rename
detection, so we can still avoid downloading the blobs for irrelevant
sources. Rename prefetch() to inexact_prefetch(), and introduce a
new basename_prefetch() to take advantage of this.
If we modify the testcase from commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2021-01-23)
to pass
--sparse --filter=blob:none
to the clone command, and use the new trace2 "fetch_count" output from
a few commits ago to track both the number of fetch subcommands invoked
and the number of objects fetched across all those fetches, then for
the mega-renames testcase we observe the following:
BEFORE this commit, rebasing 35 patches:
strategy # of fetches total # of objects fetched
--------- ------------ --------------------------
recursive 62 11423
ort 30 11391
AFTER this commit, rebasing the same 35 patches:
ort 32 63
This means that the new code only needs to download less than 2 blobs
per patch being rebased. That is especially interesting given that the
repository at the start only had approximately half a dozen TOTAL blobs
downloaded to start with (because the default sparse-checkout of just
the toplevel directory was in use).
So, for this particular linux kernel testcase that involved ~26,000
renames on the upstream side (drivers/ -> pilots/) across which 35
patches were being rebased, this change reduces the number of blobs that
need to be downloaded by a factor of ~180.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
estimate_similarity() was setting up a diff_populate_filespec_options
every time it was called, requiring the caller of estimate_similarity()
to pass in some data needed to set up this option. Currently the needed
data consisted of a single variable (skip_unmodified), but we want to
also have the different estimate_similarity() callsites start using
different missing_object_cb functions as well. Rather than also passing
that data in, just have the caller pass in the whole
diff_populate_filespec_options, and reduce the number of times we need to
set it up.
As a side note, this also drops the number of calls to
has_promisor_remote() dramatically. If L is the number of basename
paths to compare, M is the number of inexact sources, and N is the
number of inexact destinations, then the number of calls to
has_promisor_remote() drops from L+M*N down to at most 2 -- one for each
of the sites that calls estimate_similarity(). has_promisor_remote() is
a very fast function so this almost certainly has no measurable
performance impact, but it seems cleaner to avoid calling that function
so many times.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Optimize out repeated rename detection in a sequence of mergy
operations.
* en/ort-perf-batch-11:
merge-ort, diffcore-rename: employ cached renames when possible
merge-ort: handle interactions of caching and rename/rename(1to1) cases
merge-ort: add helper functions for using cached renames
merge-ort: preserve cached renames for the appropriate side
merge-ort: avoid accidental API mis-use
merge-ort: add code to check for whether cached renames can be reused
merge-ort: populate caches of rename detection results
merge-ort: add data structures for in-memory caching of rename detection
t6429: testcases for remembering renames
fast-rebase: write conflict state to working tree, index, and HEAD
fast-rebase: change assert() to BUG()
Documentation/technical: describe remembering renames optimization
t6423: rename file within directory that other side renamed
A random hodge-podge of incorrect or out-of-date comments that I found:
* t6423 had a comment that has referred to the wrong test for years;
fix it to refer to the right one.
* diffcore-rename had a FIXME comment meant to remind myself to
investigate if I could make another code change. I later
investigated and removed the FIXME, but while cherry-picking the
patch to submit upstream I missed the later update. Remove the
comment now.
* merge-ort had the early part of a comment for a function; I had
meant to include the more involved description when I updated the
function. Update the comment now.
Signed-off-by: Elijah Newren <newren@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The keys of break_idx are strings from the diff_filepairs of
diff_queued_diff. break_idx is only used in location_rename_dst(), and
that usage is always before any free'ing of the pairs (and thus the
strings in the pairs). As such, there is no need to strdup these keys;
we can just reuse the existing strings as-is.
The merge logic doesn't make use of break detection, so this does not
affect the performance of any of my testcases. It was just a minor
unrelated optimization noted in passing while looking at the code.
Signed-off-by: Elijah Newren <newren@gmail.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When there are many renames between the old base of a series of commits
and the new base, the way sequencer.c, merge-recursive.c, and
diffcore-rename.c have traditionally split the work resulted in
redetecting the same renames with each and every commit being
transplanted. To address this, the last several commits have been
creating a cache of rename detection results, determining when it was
safe to use such a cache in subsequent merge operations, adding helper
functions, and so on. See the previous half dozen commit messages for
additional discussion of this optimization, particularly the message a
few commits ago entitled "add code to check for whether cached renames
can be reused". This commit finally ties all of that work together,
modifying the merge algorithm to make use of these cached renames.
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:
Before After
no-renames: 5.665 s ± 0.129 s 5.622 s ± 0.059 s
mega-renames: 11.435 s ± 0.158 s 10.127 s ± 0.073 s
just-one-mega: 494.2 ms ± 6.1 ms 500.3 ms ± 3.8 ms
That's a fairly small improvement, but mostly because the previous
optimizations were so effective for these particular testcases; this
optimization only kicks in when the others don't. If we undid the
basename-guided rename detection and skip-irrelevant-renames
optimizations, then we'd see that this series by itself improved
performance as follows:
Before Basename Series After Just This Series
no-renames: 13.815 s ± 0.062 s 5.697 s ± 0.080 s
mega-renames: 1799.937 s ± 0.493 s 205.709 s ± 0.457 s
Since this optimization kicks in to help accelerate cases where the
previous optimizations do not apply, this last comparison shows that
this cached-renames optimization has the potential to help signficantly
in cases that don't meet the requirements for the other optimizations to
be effective.
The changes made in this optimization also lay some important groundwork
for a future optimization around having collect_merge_info() avoid
recursing into subtrees in more cases.
However, for this optimization to be effective, merge_switch_to_result()
should only be called when the rebase or cherry-pick operation has
either completed or hit a case where the user needs to resolve a
conflict or edit the result. If it is called after every commit, as
sequencer.c does, then the working tree and index are needlessly updated
with every commit and the cached metadata is tossed, defeating this
optimization. Refactoring sequencer.c to only call
merge_switch_to_result() at the end of the operation is a bigger
undertaking, and the practical benefits of this optimization will not be
realized until that work is performed. Since `test-tool fast-rebase`
only updates at the end of the operation, it was used to obtain the
timings above.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Various rename detection optimization to help "ort" merge strategy
backend.
* en/ort-perf-batch-10:
diffcore-rename: determine which relevant_sources are no longer relevant
merge-ort: record the reason that we want a rename for a file
diffcore-rename: add computation of number of unknown renames
diffcore-rename: check if we have enough renames for directories early on
diffcore-rename: only compute dir_rename_count for relevant directories
merge-ort: record the reason that we want a rename for a directory
merge-ort, diffcore-rename: tweak dirs_removed and relevant_source type
diffcore-rename: take advantage of "majority rules" to skip more renames
The ort merge backend has been optimized by skipping irrelevant
renames.
* en/ort-perf-batch-9:
diffcore-rename: avoid doing basename comparisons for irrelevant sources
merge-ort: skip rename detection entirely if possible
merge-ort: use relevant_sources to filter possible rename sources
merge-ort: precompute whether directory rename detection is needed
merge-ort: introduce wrappers for alternate tree traversal
merge-ort: add data structures for an alternate tree traversal
merge-ort: precompute subset of sources for which we need rename detection
diffcore-rename: enable filtering possible rename sources
Rename detection rework continues.
* en/ort-perf-batch-8:
diffcore-rename: compute dir_rename_guess from dir_rename_counts
diffcore-rename: limit dir_rename_counts computation to relevant dirs
diffcore-rename: compute dir_rename_counts in stages
diffcore-rename: extend cleanup_dir_rename_info()
diffcore-rename: move dir_rename_counts into dir_rename_info struct
diffcore-rename: add function for clearing dir_rename_count
Move computation of dir_rename_count from merge-ort to diffcore-rename
diffcore-rename: add a mapping of destination names to their indices
diffcore-rename: provide basic implementation of idx_possible_rename()
diffcore-rename: use directory rename guided basename comparisons
As noted a few commits ago ("diffcore-rename: only compute
dir_rename_count for relevant directories"), when a source file rename
is used as part of directory rename detection, we need to increment
counts for each ancestor directory in dirs_removed with value
RELEVANT_FOR_SELF. However, a few commits ago ("diffcore-rename: check
if we have enough renames for directories early on"), we may have
downgraded all relevant ancestor directories from RELEVANT_FOR_SELF to
RELEVANT_FOR_ANCESTOR.
For a given file, if no ancestor directory is found in dirs_removed with
a value of RELEVANT_FOR_SELF, then we can downgrade
relevant_source[PATH] from RELEVANT_LOCATION to RELEVANT_NO_MORE. This
means we can skip detecting a rename for that particular path (and any
other paths in the same directory).
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:
Before After
no-renames: 5.680 s ± 0.096 s 5.665 s ± 0.129 s
mega-renames: 13.812 s ± 0.162 s 11.435 s ± 0.158 s
just-one-mega: 506.0 ms ± 3.9 ms 494.2 ms ± 6.1 ms
While this improvement looks rather modest for these testcases (because
all the previous optimizations were sufficient to nearly remove all time
spent in rename detection already), consider this alternative testcase
tweaked from the ones in commit 557ac0350d as follows
<Same initial setup as commit 557ac0350d, then...>
$ git switch -c add-empty-file v5.5
$ >drivers/gpu/drm/i915/new-empty-file
$ git add drivers/gpu/drm/i915/new-empty-file
$ git commit -m "new file"
$ git switch 5.4-rename
$ git cherry-pick --strategy=ort add-empty-file
For this testcase, we see the following improvement:
Before After
pick-empty: 1.936 s ± 0.024 s 688.1 ms ± 4.2 ms
So roughly a factor of 3 speedup. At $DAYJOB, there was a particular
repository and cherry-pick that inspired this optimization; for that
case I saw a speedup factor of 7 with this optimization.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The previous commit can only be effective if we have a computation of
the number of paths under a given directory which are still have pending
renames, and expected this number to be recorded in the dir_rename_count
map under the key UNKNOWN_DIR. Add the code necessary to compute these
values.
Note that this change means dir_rename_count might have a directory
whose only entry (for UNKNOWN_DIR) was removed by the time merge-ort
goes to check it. To account for this, merge-ort needs to check for the
case where the max count is 0.
With this change we are now computing the necessary value for each
directory in dirs_removed, but are not using that value anywhere. The
next two commits will make use of the values stored in dirs_removed in
order to compute whether each relevant_source (that is needed only for
directory rename detection) has become unnecessary.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
As noted in the past few commits, if we can determine that a directory
already has enough renames to determine how directory rename detection
will be decided for that directory, then we can mark that directory as
no longer needing any more renames detected for files underneath it.
For such directories, we change the value in the dirs_removed map from
RELEVANT_TO_SELF to RELEVANT_FOR_ANCESTOR.
A subsequent patch will use this information while iterating over the
remaining potential rename sources to mark ones that were only
location_relevant as unneeded if no containing directory is still marked
as RELEVANT_TO_SELF.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When one side adds files to a directory that the other side renamed,
directory rename detection is used to either move the new paths to the
newer directory or warn the user about the fact that another path
location might be better.
If a parent of the given directory had new files added to it, any
renames in the current directory are also part of determining where the
parent directory is renamed to. Thus, naively, we need to record each
rename N times for a path at depth N. However, we can use the
additional information added to dirs_removed in the last commit to avoid
traversing all N parent directories in many cases. Let's use an example
to explain how this works. If we have a path named
src/old_dir/a/b/file.c
and src/old_dir doesn't exist on one side of history, but the other
added a file named src/old_dir/newfile.c, then if one side renamed
src/old_dir/a/b/file.c => source/new_dir/a/b/file.c
then this file would affect potential directory rename detection counts
for
src/old_dir/a/b => source/new_dir/a/b
src/old_dir/a => source/new_dir/a
src/old_dir => source/new_dir
src => source
adding a weight of 1 to each in dir_rename_counts. However, if src/
exists on both sides of history, then we don't need to track any entries
for it in dir_rename_counts. That was implemented previously. What we
are adding now, is that if no new files were added to src/old_dir/a or
src/old_dir/b, then we don't need to have counts in dir_rename_count
for those directories either.
In short, we only need to track counts in dir_rename_count for
directories whose dirs_removed value is RELEVANT_FOR_SELF. And as soon
as we reach a directory that isn't in dirs_removed (signalled by
returning the default value of NOT_RELEVANT from strintmap_get()), we
can stop looking any further up the directory hierarchy.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When one side of history renames a directory, and the other side of
history added files to the old directory, directory rename detection is
used to warn about the location of the added files so the user can
move them to the old directory or keep them with the new one.
This sets up three different types of directories:
* directories that had new files added to them
* directories underneath a directory that had new files added to them
* directories where no new files were added to it or any leading path
Save this information in dirs_removed; the next several commits will
make use of this information.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
As noted in the previous commit, we want to be able to take advantage of
the "majority rules" portion of directory rename detection to avoid
detecting more renames than necessary. However, for diffcore-rename to
take advantage of that, it needs to know whether a rename source file
was needed for just directory rename detection reasons, or if it is
wanted for potential three-way content merging. Modify relevant_sources
from a strset to a strintmap, so we can encode additional information.
We also modify dirs_removed from a strset to a strintmap at the same
time because trying to determine what files are needed for directory
rename detection will require us tracking a bit more information for
each directory.
This commit only changes the types of the two variables from strset to
strintmap; it does not actually store any special values yet and for now
only checks for presence of entries in the strintmap. Thus, the code is
functionally identical to how it behaved before. Future commits will
start associating values with each key for these two maps.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In directory rename detection (when a directory is removed on one side
of history and the other side adds new files to that directory), we work
to find where the greatest number of files within that directory were
renamed to so that the new files can be moved with the majority of the
files.
Naively, we can just do this by detecting renames for *all* files within
the removed/renamed directory, looking at all the destination
directories where files within that directory were moved, and if there
is more than one such directory then taking the one with the greatest
number of files as the directory where the old directory was renamed to.
However, sometimes there are enough renames from exact rename detection
or basename-guided rename detection that we have enough information to
determine the majority winner already. Add a function meant to compute
whether particular renames are still needed based on this majority rules
check. The next several commits will then add the necessary
infrastructure to get the information we need to compute which
additional rename sources we can skip.
An important side note for future further optimization:
There is a possible improvement to this optimization that I have not yet
attempted and will not be included in this series of patches: we could
first check whether exact renames provide enough information for us to
determine directory renames, and avoid doing basename-guided rename
detection on some or all of the RELEVANT_LOCATION files within those
directories. In effect, this variant would mean doing the
handle_early_known_dir_renames() both after exact rename detection and
again after basename-guided rename detection, though it would also mean
decrementing the number of "unknown" renames for each rename we found
from basename-guided rename detection. Adding this additional check for
skippable renames right after exact rename detection might turn out to
be valuable, especially for partial clones where it might allow us to
download certain source files entirely. However, this particular
optimization was actually the last one I did in original implementation
order, and by the time I implemented this idea, every testcase I had was
sufficiently fast that further optimization was unwarranted. If future
testcases arise that tax rename detection more heavily (or perhaps
partial clones can benefit from avoiding loading more objects), it may
be worth implementing this more involved variant.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add and apply a semantic patch for converting code that open-codes
CALLOC_ARRAY to use it instead. It shortens the code and infers the
element size automatically.
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The basename comparison optimization implemented in
find_basename_matches() is very beneficial since it allows a source to
sometimes only be compared with one other file instead of N other files.
When a match is found, both a source and destination can be removed from
the matrix of inexact rename comparisons. In contrast, the irrelevant
source optimization only allows us to remove a source from the matrix of
inexact rename comparisons...but it has the advantage of allowing a
source file to not even be loaded into memory at all and be compared to
0 other files. Generally, not even comparing is a bigger performance
win, so when both optimizations could apply, prefer to use the
irrelevant-source optimization.
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:
Before After
no-renames: 5.708 s ± 0.111 s 5.680 s ± 0.096 s
mega-renames: 102.171 s ± 0.440 s 13.812 s ± 0.162 s
just-one-mega: 3.471 s ± 0.015 s 506.0 ms ± 3.9 ms
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add the ability to diffcore_rename_extended() to allow external callers
to declare that they only need renames detected for a subset of source
files, and use that information to skip detecting renames for them.
There are two important pieces to this optimization that may not be
obvious at first glance:
* We do not require callers to just filter the filepairs out
to remove the non-relevant sources, because exact rename detection
is fast and when it finds a match it can remove both a source and a
destination whereas the relevant_sources filter can only remove a
source.
* We need to filter out the source pairs in a preliminary pass instead
of adding a
strset_contains(relevant_sources, one->path)
check within the nested matrix loop. The reason for that is if we
have 30k renames, doing 30k * 30k = 900M strset_contains() calls
becomes extraordinarily expensive and defeats the performance gains
from this change; we only want to do 30k such calls instead.
If callers pass NULL for relevant_sources, that is special cases to
treat all sources as relevant. Since all callers currently pass NULL,
this optimization does not yet have any effect. Subsequent commits will
have merge-ort compute a set of relevant_sources to restrict which
sources we detect renames for, and have merge-ort pass that set of
relevant_sources to diffcore_rename_extended().
A note about filtering order:
Some may be curious why we don't filter out irrelevant sources at the
same time we filter out exact renames. While that technically could be
done at this point, there are two reasons to defer it:
First, was to reinforce a lesson that was too easy to forget. As I
mentioned above, in the past I filtered irrelevant sources out before
exact rename checking, and then discovered that exact renames' ability
to remove both sources and destinations was an important consideration
and thus doing the filtering after exact rename checking would speed
things up. Then at some point I realized that basename matching could
also remove both sources and destinations, and decided to put irrelevant
source filtering after basename filtering. That slowed things down a
lot. But, despite learning about this important ordering, in later
restructuring I forgot and made the same mistake of putting the
filtering after basename guided rename detection again. So, I have this
series of patches structured to do the irrelevant filtering last to
start to show how much extra it costs, and then add relevant filtering
in to find_basename_matches() to show how much it speeds things up.
Basically, it's a way to reinforce something that apparently was too
easy to forget, and make sure the commit messages record this lesson.
Second, the items in the "relevant_sources" in this patch series will
include all sources that *might be* relevant. It has to be conservative
and catch anything that might need a rename, but in the patch series
after this one we'll find ways to weed out more of the *might be*
relevant ones. Unfortunately, merge-ort does not have sufficient
information to weed those ones out, and there isn't enough information
at the time of filtering exact renames out to remove the extra ones
either. It has to be deferred. So the deferral is in part to simplify
some later additions.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
dir_rename_counts has a mapping of a mapping, in particular, it has
old_dir => { new_dir => count }
We want a simple mapping of
old_dir => new_dir
based on which new_dir had the highest count for a given old_dir.
Compute this and store it in dir_rename_guess.
This is the final piece of the puzzle needed to make our guesses at
which directory files have been moved to when basenames aren't unique.
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:
Before After
no-renames: 12.775 s ± 0.062 s 12.596 s ± 0.061 s
mega-renames: 188.754 s ± 0.284 s 130.465 s ± 0.259 s
just-one-mega: 5.599 s ± 0.019 s 3.958 s ± 0.010 s
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We are using dir_rename_counts to count the number of other directories
that files within a directory moved to. We only need this information
for directories that disappeared, though, so we can return early from
update_dir_rename_counts() for other paths.
If dirs_removed is passed to diffcore_rename_extended(), then it
provides the relevant bits of information for us to limit this counting
to relevant dirs. If dirs_removed is not passed, we would need to
compute some replacement in order to do this limiting. Introduce a new
info->relevant_source_dirs variable for this purpose, even though at
this stage we will only set it to dirs_removed for simplicity.
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Compute dir_rename_counts based just on exact renames to start, as that
can provide us useful information in find_basename_matches(). This is
done by moving the code from compute_dir_rename_counts() into
initialize_dir_rename_info(), resulting in it being computed earlier and
based just on exact renames. Since that's an incomplete result, we
augment the counts via calling update_dir_rename_counts() after each
basename-guide and inexact rename detection match is found.
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When diffcore_rename_extended() is passed a NULL dir_rename_count, we
will still want to create a temporary one for use by
find_basename_matches(), but have it fully deallocated before
diffcore_rename_extended() returns. However, when
diffcore_rename_extended() is passed a dir_rename_count, we want to fill
that strmap with appropriate values and return it. However, for our
interim purposes we may also add entries corresponding to directories
that cannot have been renamed due to still existing on both sides.
Extend cleanup_dir_rename_info() to handle these two different cases,
cleaning up the relevant bits of information for each case.
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This continues the migration of the directory rename detection code into
diffcore-rename, now taking the simple step of combining it with the
dir_rename_info struct. Future commits will then make dir_rename_counts
be computed in stages, and add computation of dir_rename_guess.
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
As we adjust the usage of dir_rename_count we want to have a function
for clearing, or partially clearing it out. Add a
partial_clear_dir_rename_count() function for this purpose.
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Move the computation of dir_rename_count from merge-ort.c to
diffcore-rename.c, making slight adjustments to the data structures
based on the move. While the diffstat looks large, viewing this commit
with --color-moved makes it clear that only about 20 lines changed.
With this patch, the computation of dir_rename_count is still only done
after inexact rename detection, but subsequent commits will add a
preliminary computation of dir_rename_count after exact rename
detection, followed by some updates after inexact rename detection.
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Compute a mapping of full filename to the index within rename_dst where
that filename is found, and store it in idx_map. idx_possible_rename()
needs this to quickly finding an array entry in rename_dst given the
pathname.
While at it, add placeholder initializations for dir_rename_count and
dir_rename_guess; these will be more fully populated in subsequent
commits.
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a new struct dir_rename_info with various values we need inside our
idx_possible_rename() function introduced in the previous commit. Add a
basic implementation for this function showing how we plan to use the
variables, but which will just return early with a value of -1 (not
found) when those variables are not set up.
Future commits will do the work necessary to set up those other
variables so that idx_possible_rename() does not always return -1.
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
A previous commit noted that it is very common for people to move files
across directories while keeping their filename the same. The last few
commits took advantage of this and showed that we can accelerate rename
detection significantly using basenames; since files with the same
basename serve as likely rename candidates, we can check those first and
remove them from the rename candidate pool if they are sufficiently
similar.
Unfortunately, the previous optimization was limited by the fact that
the remaining basenames after exact rename detection are not always
unique. Many repositories have hundreds of build files with the same
name (e.g. Makefile, .gitignore, build.gradle, etc.), and may even have
hundreds of source files with the same name. (For example, the linux
kernel has 100 setup.c, 87 irq.c, and 112 core.c files. A repository at
$DAYJOB has a lot of ObjectFactory.java and Plugin.java files).
For these files with non-unique basenames, we are faced with the task of
attempting to determine or guess which directory they may have been
relocated to. Such a task is precisely the job of directory rename
detection. However, there are two catches: (1) the directory rename
detection code has traditionally been part of the merge machinery rather
than diffcore-rename.c, and (2) directory rename detection currently
runs after regular rename detection is complete. The 1st catch is just
an implementation issue that can be overcome by some code shuffling.
The 2nd requires us to add a further approximation: we only have access
to exact renames at this point, so we need to do directory rename
detection based on just exact renames. In some cases we won't have
exact renames, in which case this extra optimization won't apply. We
also choose to not apply the optimization unless we know that the
underlying directory was removed, which will require extra data to be
passed in to diffcore_rename_extended(). Also, even if we get a
prediction about which directory a file may have relocated to, we will
still need to check to see if there is a file in the predicted
directory, and then compare the two files to see if they meet the higher
min_basename_score threshold required for marking the two files as
renames.
This commit introduces an idx_possible_rename() function which will
do this directory rename detection for us and give us the index within
rename_dst of the resulting filename. For now, this function is
hardcoded to return -1 (not found) and just hooks up how its results
would be used once we have a more complete implementation in place.
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Make use of the new find_basename_matches() function added in the last
two patches, to find renames more rapidly in cases where we can match up
files based on basenames. As a quick reminder (see the last two commit
messages for more details), this means for example that
docs/extensions.txt and docs/config/extensions.txt are considered likely
renames if there are no remaining 'extensions.txt' files elsewhere among
the added and deleted files, and if a similarity check confirms they are
similar, then they are marked as a rename without looking for a better
similarity match among other files. This is a behavioral change, as
covered in more detail in the previous commit message.
We do not use this heuristic together with either break or copy
detection. The point of break detection is to say that filename
similarity does not imply file content similarity, and we only want to
know about file content similarity. The point of copy detection is to
use more resources to check for additional similarities, while this is
an optimization that uses far less resources but which might also result
in finding slightly fewer similarities. So the idea behind this
optimization goes against both of those features, and will be turned off
for both.
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:
Before After
no-renames: 13.815 s ± 0.062 s 13.294 s ± 0.103 s
mega-renames: 1799.937 s ± 0.493 s 187.248 s ± 0.882 s
just-one-mega: 51.289 s ± 0.019 s 5.557 s ± 0.017 s
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
It is not uncommon in real world repositories for the majority of file
renames to not change the basename of the file; i.e. most "renames" are
just a move of files into different directories. We can make use of
this to avoid comparing all rename source candidates with all rename
destination candidates, by first comparing sources to destinations with
the same basenames. If two files with the same basename are
sufficiently similar, we record the rename; if not, we include those
files in the more exhaustive matrix comparison.
This means we are adding a set of preliminary additional comparisons,
but for each file we only compare it with at most one other file. For
example, if there was a include/media/device.h that was deleted and a
src/module/media/device.h that was added, and there are no other
device.h files in the remaining sets of added and deleted files after
exact rename detection, then these two files would be compared in the
preliminary step.
This commit does not yet actually employ this new optimization, it
merely adds a function which can be used for this purpose. The next
commit will do the necessary plumbing to make use of it.
Note that this optimization might give us different results than without
the optimization, because it's possible that despite files with the same
basename being sufficiently similar to be considered a rename, there's
an even better match between files without the same basename. I think
that is okay for four reasons: (1) it's easy to explain to the users
what happened if it does ever occur (or even for them to intuitively
figure out), (2) as the next patch will show it provides such a large
performance boost that it's worth the tradeoff, and (3) it's somewhat
unlikely that despite having unique matching basenames that other files
serve as better matches. Reason (4) takes a full paragraph to
explain...
If the previous three reasons aren't enough, consider what rename
detection already does. Break detection is not the default, meaning
that if files have the same _fullname_, then they are considered related
even if they are 0% similar. In fact, in such a case, we don't even
bother comparing the files to see if they are similar let alone
comparing them to all other files to see what they are most similar to.
Basically, we override content similarity based on sufficient filename
similarity. Without the filename similarity (currently implemented as
an exact match of filename), we swing the pendulum the opposite
direction and say that filename similarity is irrelevant and compare a
full N x M matrix of sources and destinations to find out which have the
most similar contents. This optimization just adds another form of
filename similarity comparison, but augments it with a file content
similarity check as well. Basically, if two files have the same
basename and are sufficiently similar to be considered a rename, mark
them as such without comparing the two to all other rename candidates.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We want to make use of unique basenames among remaining source and
destination files to help inform rename detection, so that more likely
pairings can be checked first. (src/moduleA/foo.txt and
source/module/A/foo.txt are likely related if there are no other
'foo.txt' files among the remaining deleted and added files.) Add a new
function, not yet used, which creates a map of the unique basenames
within rename_src and another within rename_dst, together with the
indices within rename_src/rename_dst where those basenames show up.
Non-unique basenames still show up in the map, but have an invalid index
(-1).
This function was inspired by the fact that in real world repositories,
files are often moved across directories without changing names. Here
are some sample repositories and the percentage of their historical
renames (as of early 2020) that preserved basenames:
* linux: 76%
* gcc: 64%
* gecko: 79%
* webkit: 89%
These statistics alone don't prove that an optimization in this area
will help or how much it will help, since there are also unpaired adds
and deletes, restrictions on which basenames we consider, etc., but it
certainly motivated the idea to try something in this area.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We have to look at each entry in rename_src a total of rename_dst_nr
times. When we're not detecting copies, any exact renames or ignorable
rename paths will just be skipped over. While checking that these can
be skipped over is a relatively cheap check, it's still a waste of time
to do that check more than once, let alone rename_dst_nr times. When
rename_src_nr is a few thousand times bigger than the number of relevant
sources (such as when cherry-picking a commit that only touched a
handful of files, but from a side of history that has different names
for some high level directories), this time can add up.
First make an initial pass over the rename_src array and move all the
relevant entries to the front, so that we can iterate over just those
relevant entries.
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:
Before After
no-renames: 14.119 s ± 0.101 s 13.815 s ± 0.062 s
mega-renames: 1802.044 s ± 0.828 s 1799.937 s ± 0.493 s
just-one-mega: 51.391 s ± 0.028 s 51.289 s ± 0.019 s
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diffcore_rename() had some code to avoid having destination paths that
already had an exact rename detected from being re-checked for other
renames. Source paths, however, were re-checked because we wanted to
allow the possibility of detecting copies. But if copy detection isn't
turned on, then this merely amounts to attempting to find a
better-than-exact match, which naturally ends up being an expensive
no-op. In particular, copy detection is never turned on by the merge
machinery.
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
this change improves the performance as follows:
Before After
no-renames: 14.263 s ± 0.053 s 14.119 s ± 0.101 s
mega-renames: 5504.231 s ± 5.150 s 1802.044 s ± 0.828 s
just-one-mega: 158.534 s ± 0.498 s 51.391 s ± 0.028 s
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add some timing instrumentation for both merge-ort and diffcore-rename;
I used these to measure and optimize performance in both, and several
future patch series will build on these to reduce the timings of some
select testcases.
=== Setup ===
The primary testcase I used involved rebasing a random topic in the
linux kernel (consisting of 35 patches) against an older version. I
added two variants, one where I rename a toplevel directory, and another
where I only rebase one patch instead of the whole topic. The setup is
as follows:
$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
$ git branch hwmon-updates fd8bdb23b91876ac1e624337bb88dc1dcc21d67e
$ git branch hwmon-just-one fd8bdb23b91876ac1e624337bb88dc1dcc21d67e~34
$ git branch base 4703d9119972bf586d2cca76ec6438f819ffa30e
$ git switch -c 5.4-renames v5.4
$ git mv drivers pilots # Introduce over 26,000 renames
$ git commit -m "Rename drivers/ to pilots/"
$ git config merge.renameLimit 30000
$ git config merge.directoryRenames true
=== Testcases ===
Now with REBASE standing for either "git rebase [--merge]" (using
merge-recursive) or "test-tool fast-rebase" (using merge-ort), the
testcases are:
Testcase #1: no-renames
$ git checkout v5.4^0
$ REBASE --onto HEAD base hwmon-updates
Note: technically the name is misleading; there are some renames, but
very few. Rename detection only takes about half the overall time.
Testcase #2: mega-renames
$ git checkout 5.4-renames^0
$ REBASE --onto HEAD base hwmon-updates
Testcase #3: just-one-mega
$ git checkout 5.4-renames^0
$ REBASE --onto HEAD base hwmon-just-one
=== Timing results ===
Overall timings, using hyperfine (1 warmup run, 3 runs for mega-renames,
10 runs for the other two cases):
merge-recursive merge-ort
no-renames: 18.912 s ± 0.174 s 14.263 s ± 0.053 s
mega-renames: 5964.031 s ± 10.459 s 5504.231 s ± 5.150 s
just-one-mega: 149.583 s ± 0.751 s 158.534 s ± 0.498 s
A single re-run of each with some breakdowns:
--- no-renames ---
merge-recursive merge-ort
overall runtime: 19.302 s 14.257 s
inexact rename detection: 7.603 s 7.906 s
everything else: 11.699 s 6.351 s
--- mega-renames ---
merge-recursive merge-ort
overall runtime: 5950.195 s 5499.672 s
inexact rename detection: 5746.309 s 5487.120 s
everything else: 203.886 s 17.552 s
--- just-one-mega ---
merge-recursive merge-ort
overall runtime: 151.001 s 158.582 s
inexact rename detection: 143.448 s 157.835 s
everything else: 7.553 s 0.747 s
=== Timing observations ===
0) Maximum speedup
The "everything else" row represents the maximum speedup we could
achieve if we were to somehow infinitely parallelize inexact rename
detection, but leave everything else alone. The fact that this is so
much smaller than the real runtime (even in the case with virtually no
renames) makes it clear just how overwhelmingly large the time spent on
rename detection can be.
1) no-renames
1a) merge-ort is faster than merge-recursive, which is nice. However,
this still should not be considered good enough. Although the "merge"
backend to rebase (merge-recursive) is sometimes faster than the "apply"
backend, this is one of those cases where it is not. In fact, even
merge-ort is slower. The "apply" backend can complete this testcase in
6.940 s ± 0.485 s
which is about 2x faster than merge-ort and 3x faster than
merge-recursive. One goal of the merge-ort performance work will be to
make it faster than git-am on this (and similar) testcases.
2) mega-renames
2a) Obviously rename detection is a huge cost; it's where most the time
is spent. We need to cut that down. If we could somehow infinitely
parallelize it and drive its time to 0, the merge-recursive time would
drop to about 204s, and the merge-ort time would drop to about 17s. I
think this particular stat shows I've subtly baked a couple performance
improvements into merge-ort and into fast-rebase already.
3) just-one-mega
3a) not much to say here, it just gives some flavor for how rebasing
only one patch compares to rebasing 35.
=== Goals ===
This patch is obviously just the beginning. Here are some of my goals
that this measurement will help us achieve:
* Drive the cost of rename detection down considerably for merges
* After the above has been achieved, see if there are other slowness
factors (which would have previously been overshadowed by rename
detection costs) which we can then focus on and also optimize.
* Ensure our rebase testcase that requires little rename detection
is noticeably faster with merge-ort than with apply-based rebase.
Signed-off-by: Elijah Newren <newren@gmail.com>
Acked-by: Taylor Blau <ttaylorr@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Commit 25d5ea410f ("[PATCH] Redo rename/copy detection logic.",
2005-05-24) added a duplicate entry check on rename_src in order to
avoid segfaults; the code at the time was prone to double free()s and an
easy way to avoid it was just to turn off rename detection for any
duplicate entries. Note that the form of the check was modified two
commits ago in this series.
Similarly, commit 4d6be03b95 ("diffcore-rename: avoid processing
duplicate destinations", 2015-02-26) added a duplicate entry check
on rename_dst for the exact same reason -- the code was prone to double
free()s, and an easy way to avoid it was just to turn off rename
detection entirely. Note that the form of the check was modified in the
commit just before this one.
In the original code in both places, the code was dealing with
individual diff_filespecs and trying to match things up, instead of just
keeping the original diff_filepairs around as we do now. The
intervening change in structure has fixed the accounting problems and
the associated double free()s that used to occur, and thus we already
have a better fix. As such, we can remove the band-aid checks for
duplicate entries.
Due to the last two patches, the diffcore_rename() setup is no longer a
sizeable chunk of overall runtime. Thus, in a large rebase of many
commits with lots of renames and several optimizations to inexact rename
detection, this patch only speeds up the overall code by about half a
percent or so and is pretty close to the run-to-run variability making
it hard to get an exact measurement. However, with some trace2 regions
around the setup code in diffcore_rename() so that I can focus on just
it, I measure that this patch consistently saves almost a third of the
remaining time spent in diffcore_rename() setup.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
register_rename_src() simply references the passed pair inside
rename_src. In contrast, add_rename_dst() did something entirely
different for rename_dst. Instead of copying the passed pair, it made a
copy of the second diff_filespec from the passed pair, referenced it,
and then set the diff_rename_dst.pair field to NULL. Later, when a
pairing is found, record_rename_pair() allocated a full diff_filepair
via diff_queue() and pointed its src and dst fields at the appropriate
diff_filespecs. This contrast between register_rename_src() for the
rename_src data structure and add_rename_dst() for the rename_dst data
structure is oddly inconsistent and requires more memory and work than
necessary. Let's just reference the original diff_filepair in
rename_dst as-is, just as we do with rename_src. Add a new
rename_dst.is_rename field, since the rename_dst.p field is never NULL
unlike the old rename_dst.pair field.
Taking advantage of this change and the fact that same-named paths will
be adjacent, we can get rid of the sorting of the array and most of the
lookups on it, allowing us to instead just append as we go. However,
there is one remaining reason to still keep locate_rename_dst():
handling broken pairs (i.e. when break detection is on). Those are
somewhat rare, but we can set up a simple strintmap to get the map
between the source and the index. Doing that allows us to still have a
fast lookup without sorting the rename_dst array. Since the sorting had
been done in a weakly quadratic manner, when many renames are involved
this time could add up.
There is still a strcmp() in add_rename_dst() that I have left in place
to make it easier to verify that the algorithm has the same results.
This strcmp() is there to check for duplicate destination entries (which
was the easiest way at the time to avoid segfaults in the
diffcore-rename code when trees had multiple entries at a given path).
The underlying double free()s are no longer an issue with the new
algorithm, but that can be addressed in a subsequent commit.
This patch is being submitted in a different order than its original
development, but in a large rebase of many commits with lots of renames
and with several optimizations to inexact rename detection, both setup
time and write back to output queue time from diffcore_rename() were
sizeable chunks of overall runtime. This patch accelerated the setup
time by about 65%, and final write back to the output queue time by
about 50%, resulting in an overall drop of 3.5% on the execution time of
rebasing a few dozen patches.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
register_rename_src() took pains to create an array in rename_src which
was sorted by pathname of the contained diff_filepair. The sorting was
entirely unnecessary since callers pass filepairs to us in sorted
order. We can simply append to the end of the rename_src array,
speeding up diffcore_rename() setup time.
Also, note that I dropped the return type on the function since it was
unconditionally discarded anyway.
This patch is being submitted in a different order than its original
development, but in a large rebase of many commits with lots of renames
and with several optimizations to inexact rename detection,
diffcore_rename() setup time was a sizeable chunk of overall runtime.
This patch dropped execution time of rebasing 35 commits with lots of
renames by 2% overall.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Inexact rename detection works by comparing all sources to all
destinations, computing similarities, and then finding the best matches
among those that are sufficiently similar.
However, it is preceded by exact rename detection that works by
checking if there are files with identical hashes. If exact renames are
found, we can exclude some files from inexact rename detection.
The inexact rename detection loops over the full set of files, but
immediately skips those for which rename_dst[i].is_rename is true and
thus doesn't compare any sources to that destination. As such, these
paths shouldn't be included in the progress counter.
For the eagle eyed, this change hints at an actual optimization -- the
first one I presented at Git Merge 2020. I'll be submitting that
optimization later, once the basic merge-ort algorithm has merged.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diffcore-rename had two different checks of the form
if ((a < limit || b < limit) &&
a * b <= limit * limit)
This can be simplified to
if (st_mult(a, b) <= st_mult(limit, limit))
which makes it clearer how we are checking for overflow, and makes it
much easier to parse given the drop from 8 to 4 variable appearances.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Junio C Hamano
Elijah Newren
Andrzej Hunt
René Scharfe