combine-diff: speed it up, by using multiparent diff tree-walker directly

As was recently shown in "combine-diff: optimize
combine_diff_path sets intersection", combine-diff runs very slowly. In
that commit we optimized paths sets intersection, but that accounted
only for ~ 25% of the slowness, and as my tracing showed, for linux.git
v3.10..v3.11, for merges a lot of time is spent computing
diff(commit,commit^2) just to only then intersect that huge diff to
almost small set of files from diff(commit,commit^1).

In previous commit, we described the problem in more details, and
reworked the diff tree-walker to be general one - i.e. to work in
multiple parent case too. Now is the time to take advantage of it for
finding paths for combine diff.

The implementation is straightforward - if we know, we can get generated
diff paths directly, and at present that means no diff filtering or
rename/copy detection was requested(*), we can call multiparent tree-walker
directly and get ready paths.

(*) because e.g. at present, all diffcore transformations work on
    diff_filepair queues, but in the future, that limitation can be
    lifted, if filters would operate directly on combine_diff_paths.

Timings for `git log --raw --no-abbrev --no-renames` without `-c` ("git log")
and with `-c` ("git log -c") and with `-c --merges` ("git log -c --merges")
before and after the patch are as follows:

                linux.git v3.10..v3.11

            log     log -c     log -c --merges

    before  1.9s    16.4s      15.2s
    after   1.9s     2.4s       1.1s

The result stayed the same.

Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Kirill Smelkov 2014-02-24 20:21:51 +04:00 коммит произвёл Junio C Hamano
Родитель 72441af7c4
Коммит 7195fbfaf5
2 изменённых файлов: 84 добавлений и 5 удалений

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@ -1303,7 +1303,7 @@ static const char *path_path(void *obj)
/* find set of paths that every parent touches */
static struct combine_diff_path *find_paths(const unsigned char *sha1,
static struct combine_diff_path *find_paths_generic(const unsigned char *sha1,
const struct sha1_array *parents, struct diff_options *opt)
{
struct combine_diff_path *paths = NULL;
@ -1316,6 +1316,7 @@ static struct combine_diff_path *find_paths(const unsigned char *sha1,
/* tell diff_tree to emit paths in sorted (=tree) order */
opt->orderfile = NULL;
/* D(A,P1...Pn) = D(A,P1) ^ ... ^ D(A,Pn) (wrt paths) */
for (i = 0; i < num_parent; i++) {
/*
* show stat against the first parent even when doing
@ -1346,6 +1347,35 @@ static struct combine_diff_path *find_paths(const unsigned char *sha1,
}
/*
* find set of paths that everybody touches, assuming diff is run without
* rename/copy detection, etc, comparing all trees simultaneously (= faster).
*/
static struct combine_diff_path *find_paths_multitree(
const unsigned char *sha1, const struct sha1_array *parents,
struct diff_options *opt)
{
int i, nparent = parents->nr;
const unsigned char **parents_sha1;
struct combine_diff_path paths_head;
struct strbuf base;
parents_sha1 = xmalloc(nparent * sizeof(parents_sha1[0]));
for (i = 0; i < nparent; i++)
parents_sha1[i] = parents->sha1[i];
/* fake list head, so worker can assume it is non-NULL */
paths_head.next = NULL;
strbuf_init(&base, PATH_MAX);
diff_tree_paths(&paths_head, sha1, parents_sha1, nparent, &base, opt);
strbuf_release(&base);
free(parents_sha1);
return paths_head.next;
}
void diff_tree_combined(const unsigned char *sha1,
const struct sha1_array *parents,
int dense,
@ -1355,6 +1385,7 @@ void diff_tree_combined(const unsigned char *sha1,
struct diff_options diffopts;
struct combine_diff_path *p, *paths;
int i, num_paths, needsep, show_log_first, num_parent = parents->nr;
int need_generic_pathscan;
/* nothing to do, if no parents */
if (!num_parent)
@ -1377,11 +1408,58 @@ void diff_tree_combined(const unsigned char *sha1,
/* find set of paths that everybody touches
*
* NOTE find_paths() also handles --stat, as it computes
* diff(sha1,parent_i) for all i to do the job, specifically
* for parent0.
* NOTE
*
* Diffcore transformations are bound to diff_filespec and logic
* comparing two entries - i.e. they do not apply directly to combine
* diff.
*
* If some of such transformations is requested - we launch generic
* path scanning, which works significantly slower compared to
* simultaneous all-trees-in-one-go scan in find_paths_multitree().
*
* TODO some of the filters could be ported to work on
* combine_diff_paths - i.e. all functionality that skips paths, so in
* theory, we could end up having only multitree path scanning.
*
* NOTE please keep this semantically in sync with diffcore_std()
*/
paths = find_paths(sha1, parents, &diffopts);
need_generic_pathscan = opt->skip_stat_unmatch ||
DIFF_OPT_TST(opt, FOLLOW_RENAMES) ||
opt->break_opt != -1 ||
opt->detect_rename ||
opt->pickaxe ||
opt->filter;
if (need_generic_pathscan) {
/*
* NOTE generic case also handles --stat, as it computes
* diff(sha1,parent_i) for all i to do the job, specifically
* for parent0.
*/
paths = find_paths_generic(sha1, parents, &diffopts);
}
else {
int stat_opt;
paths = find_paths_multitree(sha1, parents, &diffopts);
/*
* show stat against the first parent even
* when doing combined diff.
*/
stat_opt = (opt->output_format &
(DIFF_FORMAT_NUMSTAT|DIFF_FORMAT_DIFFSTAT));
if (stat_opt) {
diffopts.output_format = stat_opt;
diff_tree_sha1(parents->sha1[0], sha1, "", &diffopts);
diffcore_std(&diffopts);
if (opt->orderfile)
diffcore_order(opt->orderfile);
diff_flush(&diffopts);
}
}
/* find out number of surviving paths */
for (num_paths = 0, p = paths; p; p = p->next)

1
diff.c
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@ -4764,6 +4764,7 @@ void diffcore_fix_diff_index(struct diff_options *options)
void diffcore_std(struct diff_options *options)
{
/* NOTE please keep the following in sync with diff_tree_combined() */
if (options->skip_stat_unmatch)
diffcore_skip_stat_unmatch(options);
if (!options->found_follow) {