License cleanup: add SPDX GPL-2.0 license identifier to files with no license
Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.
By default all files without license information are under the default
license of the kernel, which is GPL version 2.
Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier. The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.
This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.
How this work was done:
Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
- file had no licensing information it it.
- file was a */uapi/* one with no licensing information in it,
- file was a */uapi/* one with existing licensing information,
Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.
The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne. Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.
The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed. Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.
Criteria used to select files for SPDX license identifier tagging was:
- Files considered eligible had to be source code files.
- Make and config files were included as candidates if they contained >5
lines of source
- File already had some variant of a license header in it (even if <5
lines).
All documentation files were explicitly excluded.
The following heuristics were used to determine which SPDX license
identifiers to apply.
- when both scanners couldn't find any license traces, file was
considered to have no license information in it, and the top level
COPYING file license applied.
For non */uapi/* files that summary was:
SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 11139
and resulted in the first patch in this series.
If that file was a */uapi/* path one, it was "GPL-2.0 WITH
Linux-syscall-note" otherwise it was "GPL-2.0". Results of that was:
SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 WITH Linux-syscall-note 930
and resulted in the second patch in this series.
- if a file had some form of licensing information in it, and was one
of the */uapi/* ones, it was denoted with the Linux-syscall-note if
any GPL family license was found in the file or had no licensing in
it (per prior point). Results summary:
SPDX license identifier # files
---------------------------------------------------|------
GPL-2.0 WITH Linux-syscall-note 270
GPL-2.0+ WITH Linux-syscall-note 169
((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause) 21
((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) 17
LGPL-2.1+ WITH Linux-syscall-note 15
GPL-1.0+ WITH Linux-syscall-note 14
((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause) 5
LGPL-2.0+ WITH Linux-syscall-note 4
LGPL-2.1 WITH Linux-syscall-note 3
((GPL-2.0 WITH Linux-syscall-note) OR MIT) 3
((GPL-2.0 WITH Linux-syscall-note) AND MIT) 1
and that resulted in the third patch in this series.
- when the two scanners agreed on the detected license(s), that became
the concluded license(s).
- when there was disagreement between the two scanners (one detected a
license but the other didn't, or they both detected different
licenses) a manual inspection of the file occurred.
- In most cases a manual inspection of the information in the file
resulted in a clear resolution of the license that should apply (and
which scanner probably needed to revisit its heuristics).
- When it was not immediately clear, the license identifier was
confirmed with lawyers working with the Linux Foundation.
- If there was any question as to the appropriate license identifier,
the file was flagged for further research and to be revisited later
in time.
In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.
Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights. The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.
Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.
In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.
Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
- a full scancode scan run, collecting the matched texts, detected
license ids and scores
- reviewing anything where there was a license detected (about 500+
files) to ensure that the applied SPDX license was correct
- reviewing anything where there was no detection but the patch license
was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
SPDX license was correct
This produced a worksheet with 20 files needing minor correction. This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.
These .csv files were then reviewed by Greg. Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected. This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.) Finally Greg ran the script using the .csv files to
generate the patches.
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2017-11-01 17:07:57 +03:00
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/* SPDX-License-Identifier: GPL-2.0 */
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2005-04-17 02:20:36 +04:00
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/* rwsem.h: R/W semaphores, public interface
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*
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* Written by David Howells (dhowells@redhat.com).
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* Derived from asm-i386/semaphore.h
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*/
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#ifndef _LINUX_RWSEM_H
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#define _LINUX_RWSEM_H
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#include <linux/linkage.h>
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#include <linux/types.h>
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#include <linux/kernel.h>
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2011-01-26 23:05:50 +03:00
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#include <linux/list.h>
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#include <linux/spinlock.h>
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2011-07-27 03:09:06 +04:00
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#include <linux/atomic.h>
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2016-04-07 18:12:26 +03:00
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#include <linux/err.h>
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2014-07-12 01:00:06 +04:00
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#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
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2014-07-14 21:27:49 +04:00
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#include <linux/osq_lock.h>
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2014-07-12 01:00:06 +04:00
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#endif
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2005-04-17 02:20:36 +04:00
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locking/rwsem: Optimize rwsem structure for uncontended lock acquisition
For an uncontended rwsem, count and owner are the only fields a task
needs to touch when acquiring the rwsem. So they are put next to each
other to increase the chance that they will share the same cacheline.
On a ThunderX2 99xx (arm64) system with 32K L1 cache and 256K L2
cache, a rwsem locking microbenchmark with one locking thread was
run to write-lock and write-unlock an array of rwsems separated 2
cachelines apart in a 1M byte memory block. The locking rates (kops/s)
of the microbenchmark when the rwsems are at various "long" (8-byte)
offsets from beginning of the cacheline before and after the patch were
as follows:
Cacheline Offset Pre-patch Post-patch
---------------- --------- ----------
0 17,449 16,588
1 17,450 16,465
2 17,450 16,460
3 17,453 16,462
4 14,867 16,471
5 14,867 16,470
6 14,853 16,464
7 14,867 13,172
Before the patch, the count and owner are 4 "long"s apart. After the
patch, they are only 1 "long" apart.
The rwsem data have to be loaded from the L3 cache for each access. It
can be seen that the locking rates are more consistent after the patch
than before. Note that for this particular system, the performance
drop happens whenever the count and owner are at an odd multiples of
"long"s apart. No performance drop was observed when only a single rwsem
was used (hot cache). So the drop is likely just an idiosyncrasy of the
cache architecture of this chip than an inherent problem with the patch.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/20190404174320.22416-12-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-04-04 20:43:20 +03:00
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/*
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* For an uncontended rwsem, count and owner are the only fields a task
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* needs to touch when acquiring the rwsem. So they are put next to each
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* other to increase the chance that they will share the same cacheline.
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*
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* In a contended rwsem, the owner is likely the most frequently accessed
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* field in the structure as the optimistic waiter that holds the osq lock
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* will spin on owner. For an embedded rwsem, other hot fields in the
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* containing structure should be moved further away from the rwsem to
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* reduce the chance that they will share the same cacheline causing
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* cacheline bouncing problem.
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*/
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2011-01-26 23:05:56 +03:00
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struct rw_semaphore {
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2016-06-04 08:26:02 +03:00
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atomic_long_t count;
|
locking/rwsem: Support optimistic spinning
We have reached the point where our mutexes are quite fine tuned
for a number of situations. This includes the use of heuristics
and optimistic spinning, based on MCS locking techniques.
Exclusive ownership of read-write semaphores are, conceptually,
just about the same as mutexes, making them close cousins. To
this end we need to make them both perform similarly, and
right now, rwsems are simply not up to it. This was discovered
by both reverting commit 4fc3f1d6 (mm/rmap, migration: Make
rmap_walk_anon() and try_to_unmap_anon() more scalable) and
similarly, converting some other mutexes (ie: i_mmap_mutex) to
rwsems. This creates a situation where users have to choose
between a rwsem and mutex taking into account this important
performance difference. Specifically, biggest difference between
both locks is when we fail to acquire a mutex in the fastpath,
optimistic spinning comes in to play and we can avoid a large
amount of unnecessary sleeping and overhead of moving tasks in
and out of wait queue. Rwsems do not have such logic.
This patch, based on the work from Tim Chen and I, adds support
for write-side optimistic spinning when the lock is contended.
It also includes support for the recently added cancelable MCS
locking for adaptive spinning. Note that is is only applicable
to the xadd method, and the spinlock rwsem variant remains intact.
Allowing optimistic spinning before putting the writer on the wait
queue reduces wait queue contention and provided greater chance
for the rwsem to get acquired. With these changes, rwsem is on par
with mutex. The performance benefits can be seen on a number of
workloads. For instance, on a 8 socket, 80 core 64bit Westmere box,
aim7 shows the following improvements in throughput:
+--------------+---------------------+-----------------+
| Workload | throughput-increase | number of users |
+--------------+---------------------+-----------------+
| alltests | 20% | >1000 |
| custom | 27%, 60% | 10-100, >1000 |
| high_systime | 36%, 30% | >100, >1000 |
| shared | 58%, 29% | 10-100, >1000 |
+--------------+---------------------+-----------------+
There was also improvement on smaller systems, such as a quad-core
x86-64 laptop running a 30Gb PostgreSQL (pgbench) workload for up
to +60% in throughput for over 50 clients. Additionally, benefits
were also noticed in exim (mail server) workloads. Furthermore, no
performance regression have been seen at all.
Based-on-work-from: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
[peterz: rej fixup due to comment patches, sched/rt.h header]
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Alex Shi <alex.shi@linaro.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: "Paul E.McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Scott J Norton" <scott.norton@hp.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <jbacik@fusionio.com>
Link: http://lkml.kernel.org/r/1399055055.6275.15.camel@buesod1.americas.hpqcorp.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-05-02 22:24:15 +04:00
|
|
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/*
|
2019-05-20 23:59:12 +03:00
|
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* Write owner or one of the read owners as well flags regarding
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* the current state of the rwsem. Can be used as a speculative
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* check to see if the write owner is running on the cpu.
|
locking/rwsem: Support optimistic spinning
We have reached the point where our mutexes are quite fine tuned
for a number of situations. This includes the use of heuristics
and optimistic spinning, based on MCS locking techniques.
Exclusive ownership of read-write semaphores are, conceptually,
just about the same as mutexes, making them close cousins. To
this end we need to make them both perform similarly, and
right now, rwsems are simply not up to it. This was discovered
by both reverting commit 4fc3f1d6 (mm/rmap, migration: Make
rmap_walk_anon() and try_to_unmap_anon() more scalable) and
similarly, converting some other mutexes (ie: i_mmap_mutex) to
rwsems. This creates a situation where users have to choose
between a rwsem and mutex taking into account this important
performance difference. Specifically, biggest difference between
both locks is when we fail to acquire a mutex in the fastpath,
optimistic spinning comes in to play and we can avoid a large
amount of unnecessary sleeping and overhead of moving tasks in
and out of wait queue. Rwsems do not have such logic.
This patch, based on the work from Tim Chen and I, adds support
for write-side optimistic spinning when the lock is contended.
It also includes support for the recently added cancelable MCS
locking for adaptive spinning. Note that is is only applicable
to the xadd method, and the spinlock rwsem variant remains intact.
Allowing optimistic spinning before putting the writer on the wait
queue reduces wait queue contention and provided greater chance
for the rwsem to get acquired. With these changes, rwsem is on par
with mutex. The performance benefits can be seen on a number of
workloads. For instance, on a 8 socket, 80 core 64bit Westmere box,
aim7 shows the following improvements in throughput:
+--------------+---------------------+-----------------+
| Workload | throughput-increase | number of users |
+--------------+---------------------+-----------------+
| alltests | 20% | >1000 |
| custom | 27%, 60% | 10-100, >1000 |
| high_systime | 36%, 30% | >100, >1000 |
| shared | 58%, 29% | 10-100, >1000 |
+--------------+---------------------+-----------------+
There was also improvement on smaller systems, such as a quad-core
x86-64 laptop running a 30Gb PostgreSQL (pgbench) workload for up
to +60% in throughput for over 50 clients. Additionally, benefits
were also noticed in exim (mail server) workloads. Furthermore, no
performance regression have been seen at all.
Based-on-work-from: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
[peterz: rej fixup due to comment patches, sched/rt.h header]
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Alex Shi <alex.shi@linaro.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: "Paul E.McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Scott J Norton" <scott.norton@hp.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <jbacik@fusionio.com>
Link: http://lkml.kernel.org/r/1399055055.6275.15.camel@buesod1.americas.hpqcorp.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-05-02 22:24:15 +04:00
|
|
|
*/
|
2019-05-20 23:59:12 +03:00
|
|
|
atomic_long_t owner;
|
2019-05-20 23:59:00 +03:00
|
|
|
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
|
locking/rwsem: Optimize rwsem structure for uncontended lock acquisition
For an uncontended rwsem, count and owner are the only fields a task
needs to touch when acquiring the rwsem. So they are put next to each
other to increase the chance that they will share the same cacheline.
On a ThunderX2 99xx (arm64) system with 32K L1 cache and 256K L2
cache, a rwsem locking microbenchmark with one locking thread was
run to write-lock and write-unlock an array of rwsems separated 2
cachelines apart in a 1M byte memory block. The locking rates (kops/s)
of the microbenchmark when the rwsems are at various "long" (8-byte)
offsets from beginning of the cacheline before and after the patch were
as follows:
Cacheline Offset Pre-patch Post-patch
---------------- --------- ----------
0 17,449 16,588
1 17,450 16,465
2 17,450 16,460
3 17,453 16,462
4 14,867 16,471
5 14,867 16,470
6 14,853 16,464
7 14,867 13,172
Before the patch, the count and owner are 4 "long"s apart. After the
patch, they are only 1 "long" apart.
The rwsem data have to be loaded from the L3 cache for each access. It
can be seen that the locking rates are more consistent after the patch
than before. Note that for this particular system, the performance
drop happens whenever the count and owner are at an odd multiples of
"long"s apart. No performance drop was observed when only a single rwsem
was used (hot cache). So the drop is likely just an idiosyncrasy of the
cache architecture of this chip than an inherent problem with the patch.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/20190404174320.22416-12-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-04-04 20:43:20 +03:00
|
|
|
struct optimistic_spin_queue osq; /* spinner MCS lock */
|
locking/rwsem: Support optimistic spinning
We have reached the point where our mutexes are quite fine tuned
for a number of situations. This includes the use of heuristics
and optimistic spinning, based on MCS locking techniques.
Exclusive ownership of read-write semaphores are, conceptually,
just about the same as mutexes, making them close cousins. To
this end we need to make them both perform similarly, and
right now, rwsems are simply not up to it. This was discovered
by both reverting commit 4fc3f1d6 (mm/rmap, migration: Make
rmap_walk_anon() and try_to_unmap_anon() more scalable) and
similarly, converting some other mutexes (ie: i_mmap_mutex) to
rwsems. This creates a situation where users have to choose
between a rwsem and mutex taking into account this important
performance difference. Specifically, biggest difference between
both locks is when we fail to acquire a mutex in the fastpath,
optimistic spinning comes in to play and we can avoid a large
amount of unnecessary sleeping and overhead of moving tasks in
and out of wait queue. Rwsems do not have such logic.
This patch, based on the work from Tim Chen and I, adds support
for write-side optimistic spinning when the lock is contended.
It also includes support for the recently added cancelable MCS
locking for adaptive spinning. Note that is is only applicable
to the xadd method, and the spinlock rwsem variant remains intact.
Allowing optimistic spinning before putting the writer on the wait
queue reduces wait queue contention and provided greater chance
for the rwsem to get acquired. With these changes, rwsem is on par
with mutex. The performance benefits can be seen on a number of
workloads. For instance, on a 8 socket, 80 core 64bit Westmere box,
aim7 shows the following improvements in throughput:
+--------------+---------------------+-----------------+
| Workload | throughput-increase | number of users |
+--------------+---------------------+-----------------+
| alltests | 20% | >1000 |
| custom | 27%, 60% | 10-100, >1000 |
| high_systime | 36%, 30% | >100, >1000 |
| shared | 58%, 29% | 10-100, >1000 |
+--------------+---------------------+-----------------+
There was also improvement on smaller systems, such as a quad-core
x86-64 laptop running a 30Gb PostgreSQL (pgbench) workload for up
to +60% in throughput for over 50 clients. Additionally, benefits
were also noticed in exim (mail server) workloads. Furthermore, no
performance regression have been seen at all.
Based-on-work-from: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
[peterz: rej fixup due to comment patches, sched/rt.h header]
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Alex Shi <alex.shi@linaro.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: "Paul E.McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Scott J Norton" <scott.norton@hp.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <jbacik@fusionio.com>
Link: http://lkml.kernel.org/r/1399055055.6275.15.camel@buesod1.americas.hpqcorp.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-05-02 22:24:15 +04:00
|
|
|
#endif
|
locking/rwsem: Optimize rwsem structure for uncontended lock acquisition
For an uncontended rwsem, count and owner are the only fields a task
needs to touch when acquiring the rwsem. So they are put next to each
other to increase the chance that they will share the same cacheline.
On a ThunderX2 99xx (arm64) system with 32K L1 cache and 256K L2
cache, a rwsem locking microbenchmark with one locking thread was
run to write-lock and write-unlock an array of rwsems separated 2
cachelines apart in a 1M byte memory block. The locking rates (kops/s)
of the microbenchmark when the rwsems are at various "long" (8-byte)
offsets from beginning of the cacheline before and after the patch were
as follows:
Cacheline Offset Pre-patch Post-patch
---------------- --------- ----------
0 17,449 16,588
1 17,450 16,465
2 17,450 16,460
3 17,453 16,462
4 14,867 16,471
5 14,867 16,470
6 14,853 16,464
7 14,867 13,172
Before the patch, the count and owner are 4 "long"s apart. After the
patch, they are only 1 "long" apart.
The rwsem data have to be loaded from the L3 cache for each access. It
can be seen that the locking rates are more consistent after the patch
than before. Note that for this particular system, the performance
drop happens whenever the count and owner are at an odd multiples of
"long"s apart. No performance drop was observed when only a single rwsem
was used (hot cache). So the drop is likely just an idiosyncrasy of the
cache architecture of this chip than an inherent problem with the patch.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/20190404174320.22416-12-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-04-04 20:43:20 +03:00
|
|
|
raw_spinlock_t wait_lock;
|
|
|
|
|
struct list_head wait_list;
|
2019-07-29 07:47:35 +03:00
|
|
|
#ifdef CONFIG_DEBUG_RWSEMS
|
|
|
|
|
void *magic;
|
|
|
|
|
#endif
|
2011-01-26 23:05:56 +03:00
|
|
|
#ifdef CONFIG_DEBUG_LOCK_ALLOC
|
|
|
|
|
struct lockdep_map dep_map;
|
|
|
|
|
#endif
|
|
|
|
|
};
|
|
|
|
|
|
2011-01-26 23:06:03 +03:00
|
|
|
/* In all implementations count != 0 means locked */
|
|
|
|
|
static inline int rwsem_is_locked(struct rw_semaphore *sem)
|
|
|
|
|
{
|
2016-06-04 08:26:02 +03:00
|
|
|
return atomic_long_read(&sem->count) != 0;
|
2011-01-26 23:06:03 +03:00
|
|
|
}
|
|
|
|
|
|
locking/rwsem: Remove arch specific rwsem files
As the generic rwsem-xadd code is using the appropriate acquire and
release versions of the atomic operations, the arch specific rwsem.h
files will not be that much faster than the generic code as long as the
atomic functions are properly implemented. So we can remove those arch
specific rwsem.h and stop building asm/rwsem.h to reduce maintenance
effort.
Currently, only x86, alpha and ia64 have implemented architecture
specific fast paths. I don't have access to alpha and ia64 systems for
testing, but they are legacy systems that are not likely to be updated
to the latest kernel anyway.
By using a rwsem microbenchmark, the total locking rates on a 4-socket
56-core 112-thread x86-64 system before and after the patch were as
follows (mixed means equal # of read and write locks):
Before Patch After Patch
# of Threads wlock rlock mixed wlock rlock mixed
------------ ----- ----- ----- ----- ----- -----
1 29,201 30,143 29,458 28,615 30,172 29,201
2 6,807 13,299 1,171 7,725 15,025 1,804
4 6,504 12,755 1,520 7,127 14,286 1,345
8 6,762 13,412 764 6,826 13,652 726
16 6,693 15,408 662 6,599 15,938 626
32 6,145 15,286 496 5,549 15,487 511
64 5,812 15,495 60 5,858 15,572 60
There were some run-to-run variations for the multi-thread tests. For
x86-64, using the generic C code fast path seems to be a little bit
faster than the assembly version with low lock contention. Looking at
the assembly version of the fast paths, there are assembly to/from C
code wrappers that save and restore all the callee-clobbered registers
(7 registers on x86-64). The assembly generated from the generic C
code doesn't need to do that. That may explain the slight performance
gain here.
The generic asm rwsem.h can also be merged into kernel/locking/rwsem.h
with no code change as no other code other than those under
kernel/locking needs to access the internal rwsem macros and functions.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-c6x-dev@linux-c6x.org
Cc: linux-m68k@lists.linux-m68k.org
Cc: linux-riscv@lists.infradead.org
Cc: linux-um@lists.infradead.org
Cc: linux-xtensa@linux-xtensa.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: nios2-dev@lists.rocketboards.org
Cc: openrisc@lists.librecores.org
Cc: uclinux-h8-devel@lists.sourceforge.jp
Link: https://lkml.kernel.org/r/20190322143008.21313-2-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-03-22 17:30:06 +03:00
|
|
|
#define RWSEM_UNLOCKED_VALUE 0L
|
2016-06-04 08:26:02 +03:00
|
|
|
#define __RWSEM_INIT_COUNT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE)
|
2005-04-17 02:20:36 +04:00
|
|
|
|
2011-01-26 23:06:00 +03:00
|
|
|
/* Common initializer macros and functions */
|
|
|
|
|
|
|
|
|
|
#ifdef CONFIG_DEBUG_LOCK_ALLOC
|
lockdep: Introduce wait-type checks
Extend lockdep to validate lock wait-type context.
The current wait-types are:
LD_WAIT_FREE, /* wait free, rcu etc.. */
LD_WAIT_SPIN, /* spin loops, raw_spinlock_t etc.. */
LD_WAIT_CONFIG, /* CONFIG_PREEMPT_LOCK, spinlock_t etc.. */
LD_WAIT_SLEEP, /* sleeping locks, mutex_t etc.. */
Where lockdep validates that the current lock (the one being acquired)
fits in the current wait-context (as generated by the held stack).
This ensures that there is no attempt to acquire mutexes while holding
spinlocks, to acquire spinlocks while holding raw_spinlocks and so on. In
other words, its a more fancy might_sleep().
Obviously RCU made the entire ordeal more complex than a simple single
value test because RCU can be acquired in (pretty much) any context and
while it presents a context to nested locks it is not the same as it
got acquired in.
Therefore its necessary to split the wait_type into two values, one
representing the acquire (outer) and one representing the nested context
(inner). For most 'normal' locks these two are the same.
[ To make static initialization easier we have the rule that:
.outer == INV means .outer == .inner; because INV == 0. ]
It further means that its required to find the minimal .inner of the held
stack to compare against the outer of the new lock; because while 'normal'
RCU presents a CONFIG type to nested locks, if it is taken while already
holding a SPIN type it obviously doesn't relax the rules.
Below is an example output generated by the trivial test code:
raw_spin_lock(&foo);
spin_lock(&bar);
spin_unlock(&bar);
raw_spin_unlock(&foo);
[ BUG: Invalid wait context ]
-----------------------------
swapper/0/1 is trying to lock:
ffffc90000013f20 (&bar){....}-{3:3}, at: kernel_init+0xdb/0x187
other info that might help us debug this:
1 lock held by swapper/0/1:
#0: ffffc90000013ee0 (&foo){+.+.}-{2:2}, at: kernel_init+0xd1/0x187
The way to read it is to look at the new -{n,m} part in the lock
description; -{3:3} for the attempted lock, and try and match that up to
the held locks, which in this case is the one: -{2,2}.
This tells that the acquiring lock requires a more relaxed environment than
presented by the lock stack.
Currently only the normal locks and RCU are converted, the rest of the
lockdep users defaults to .inner = INV which is ignored. More conversions
can be done when desired.
The check for spinlock_t nesting is not enabled by default. It's a separate
config option for now as there are known problems which are currently
addressed. The config option allows to identify these problems and to
verify that the solutions found are indeed solving them.
The config switch will be removed and the checks will permanently enabled
once the vast majority of issues has been addressed.
[ bigeasy: Move LD_WAIT_FREE,… out of CONFIG_LOCKDEP to avoid compile
failure with CONFIG_DEBUG_SPINLOCK + !CONFIG_LOCKDEP]
[ tglx: Add the config option ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200321113242.427089655@linutronix.de
2020-03-21 14:26:01 +03:00
|
|
|
# define __RWSEM_DEP_MAP_INIT(lockname) \
|
|
|
|
|
, .dep_map = { \
|
|
|
|
|
.name = #lockname, \
|
|
|
|
|
.wait_type_inner = LD_WAIT_SLEEP, \
|
|
|
|
|
}
|
2011-01-26 23:06:00 +03:00
|
|
|
#else
|
|
|
|
|
# define __RWSEM_DEP_MAP_INIT(lockname)
|
|
|
|
|
#endif
|
|
|
|
|
|
2019-07-29 07:47:35 +03:00
|
|
|
#ifdef CONFIG_DEBUG_RWSEMS
|
|
|
|
|
# define __DEBUG_RWSEM_INITIALIZER(lockname) , .magic = &lockname
|
|
|
|
|
#else
|
|
|
|
|
# define __DEBUG_RWSEM_INITIALIZER(lockname)
|
|
|
|
|
#endif
|
|
|
|
|
|
2014-07-12 01:00:06 +04:00
|
|
|
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
|
2019-05-20 23:59:00 +03:00
|
|
|
#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED
|
locking/rwsem: Support optimistic spinning
We have reached the point where our mutexes are quite fine tuned
for a number of situations. This includes the use of heuristics
and optimistic spinning, based on MCS locking techniques.
Exclusive ownership of read-write semaphores are, conceptually,
just about the same as mutexes, making them close cousins. To
this end we need to make them both perform similarly, and
right now, rwsems are simply not up to it. This was discovered
by both reverting commit 4fc3f1d6 (mm/rmap, migration: Make
rmap_walk_anon() and try_to_unmap_anon() more scalable) and
similarly, converting some other mutexes (ie: i_mmap_mutex) to
rwsems. This creates a situation where users have to choose
between a rwsem and mutex taking into account this important
performance difference. Specifically, biggest difference between
both locks is when we fail to acquire a mutex in the fastpath,
optimistic spinning comes in to play and we can avoid a large
amount of unnecessary sleeping and overhead of moving tasks in
and out of wait queue. Rwsems do not have such logic.
This patch, based on the work from Tim Chen and I, adds support
for write-side optimistic spinning when the lock is contended.
It also includes support for the recently added cancelable MCS
locking for adaptive spinning. Note that is is only applicable
to the xadd method, and the spinlock rwsem variant remains intact.
Allowing optimistic spinning before putting the writer on the wait
queue reduces wait queue contention and provided greater chance
for the rwsem to get acquired. With these changes, rwsem is on par
with mutex. The performance benefits can be seen on a number of
workloads. For instance, on a 8 socket, 80 core 64bit Westmere box,
aim7 shows the following improvements in throughput:
+--------------+---------------------+-----------------+
| Workload | throughput-increase | number of users |
+--------------+---------------------+-----------------+
| alltests | 20% | >1000 |
| custom | 27%, 60% | 10-100, >1000 |
| high_systime | 36%, 30% | >100, >1000 |
| shared | 58%, 29% | 10-100, >1000 |
+--------------+---------------------+-----------------+
There was also improvement on smaller systems, such as a quad-core
x86-64 laptop running a 30Gb PostgreSQL (pgbench) workload for up
to +60% in throughput for over 50 clients. Additionally, benefits
were also noticed in exim (mail server) workloads. Furthermore, no
performance regression have been seen at all.
Based-on-work-from: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
[peterz: rej fixup due to comment patches, sched/rt.h header]
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Alex Shi <alex.shi@linaro.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: "Paul E.McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Scott J Norton" <scott.norton@hp.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <jbacik@fusionio.com>
Link: http://lkml.kernel.org/r/1399055055.6275.15.camel@buesod1.americas.hpqcorp.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-05-02 22:24:15 +04:00
|
|
|
#else
|
2014-07-14 21:27:52 +04:00
|
|
|
#define __RWSEM_OPT_INIT(lockname)
|
locking/rwsem: Support optimistic spinning
We have reached the point where our mutexes are quite fine tuned
for a number of situations. This includes the use of heuristics
and optimistic spinning, based on MCS locking techniques.
Exclusive ownership of read-write semaphores are, conceptually,
just about the same as mutexes, making them close cousins. To
this end we need to make them both perform similarly, and
right now, rwsems are simply not up to it. This was discovered
by both reverting commit 4fc3f1d6 (mm/rmap, migration: Make
rmap_walk_anon() and try_to_unmap_anon() more scalable) and
similarly, converting some other mutexes (ie: i_mmap_mutex) to
rwsems. This creates a situation where users have to choose
between a rwsem and mutex taking into account this important
performance difference. Specifically, biggest difference between
both locks is when we fail to acquire a mutex in the fastpath,
optimistic spinning comes in to play and we can avoid a large
amount of unnecessary sleeping and overhead of moving tasks in
and out of wait queue. Rwsems do not have such logic.
This patch, based on the work from Tim Chen and I, adds support
for write-side optimistic spinning when the lock is contended.
It also includes support for the recently added cancelable MCS
locking for adaptive spinning. Note that is is only applicable
to the xadd method, and the spinlock rwsem variant remains intact.
Allowing optimistic spinning before putting the writer on the wait
queue reduces wait queue contention and provided greater chance
for the rwsem to get acquired. With these changes, rwsem is on par
with mutex. The performance benefits can be seen on a number of
workloads. For instance, on a 8 socket, 80 core 64bit Westmere box,
aim7 shows the following improvements in throughput:
+--------------+---------------------+-----------------+
| Workload | throughput-increase | number of users |
+--------------+---------------------+-----------------+
| alltests | 20% | >1000 |
| custom | 27%, 60% | 10-100, >1000 |
| high_systime | 36%, 30% | >100, >1000 |
| shared | 58%, 29% | 10-100, >1000 |
+--------------+---------------------+-----------------+
There was also improvement on smaller systems, such as a quad-core
x86-64 laptop running a 30Gb PostgreSQL (pgbench) workload for up
to +60% in throughput for over 50 clients. Additionally, benefits
were also noticed in exim (mail server) workloads. Furthermore, no
performance regression have been seen at all.
Based-on-work-from: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
[peterz: rej fixup due to comment patches, sched/rt.h header]
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Alex Shi <alex.shi@linaro.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: "Paul E.McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Scott J Norton" <scott.norton@hp.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <jbacik@fusionio.com>
Link: http://lkml.kernel.org/r/1399055055.6275.15.camel@buesod1.americas.hpqcorp.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-05-02 22:24:15 +04:00
|
|
|
#endif
|
2011-01-26 23:06:00 +03:00
|
|
|
|
2014-07-14 21:27:52 +04:00
|
|
|
#define __RWSEM_INITIALIZER(name) \
|
2016-06-04 08:26:02 +03:00
|
|
|
{ __RWSEM_INIT_COUNT(name), \
|
2019-05-20 23:59:12 +03:00
|
|
|
.owner = ATOMIC_LONG_INIT(0), \
|
2014-07-14 21:27:52 +04:00
|
|
|
.wait_list = LIST_HEAD_INIT((name).wait_list), \
|
|
|
|
|
.wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
|
|
|
|
|
__RWSEM_OPT_INIT(name) \
|
2019-07-29 07:47:35 +03:00
|
|
|
__DEBUG_RWSEM_INITIALIZER(name) \
|
2014-07-14 21:27:52 +04:00
|
|
|
__RWSEM_DEP_MAP_INIT(name) }
|
|
|
|
|
|
2011-01-26 23:06:00 +03:00
|
|
|
#define DECLARE_RWSEM(name) \
|
|
|
|
|
struct rw_semaphore name = __RWSEM_INITIALIZER(name)
|
|
|
|
|
|
|
|
|
|
extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
|
|
|
|
|
struct lock_class_key *key);
|
|
|
|
|
|
|
|
|
|
#define init_rwsem(sem) \
|
|
|
|
|
do { \
|
|
|
|
|
static struct lock_class_key __key; \
|
|
|
|
|
\
|
|
|
|
|
__init_rwsem((sem), #sem, &__key); \
|
|
|
|
|
} while (0)
|
|
|
|
|
|
2013-08-30 18:05:22 +04:00
|
|
|
/*
|
|
|
|
|
* This is the same regardless of which rwsem implementation that is being used.
|
|
|
|
|
* It is just a heuristic meant to be called by somebody alreadying holding the
|
|
|
|
|
* rwsem to see if somebody from an incompatible type is wanting access to the
|
|
|
|
|
* lock.
|
|
|
|
|
*/
|
|
|
|
|
static inline int rwsem_is_contended(struct rw_semaphore *sem)
|
|
|
|
|
{
|
|
|
|
|
return !list_empty(&sem->wait_list);
|
|
|
|
|
}
|
|
|
|
|
|
2005-04-17 02:20:36 +04:00
|
|
|
/*
|
|
|
|
|
* lock for reading
|
|
|
|
|
*/
|
2006-07-03 11:24:53 +04:00
|
|
|
extern void down_read(struct rw_semaphore *sem);
|
2017-09-29 19:06:38 +03:00
|
|
|
extern int __must_check down_read_killable(struct rw_semaphore *sem);
|
2005-04-17 02:20:36 +04:00
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
* trylock for reading -- returns 1 if successful, 0 if contention
|
|
|
|
|
*/
|
2006-07-03 11:24:53 +04:00
|
|
|
extern int down_read_trylock(struct rw_semaphore *sem);
|
2005-04-17 02:20:36 +04:00
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
* lock for writing
|
|
|
|
|
*/
|
2006-07-03 11:24:53 +04:00
|
|
|
extern void down_write(struct rw_semaphore *sem);
|
2016-04-07 18:12:31 +03:00
|
|
|
extern int __must_check down_write_killable(struct rw_semaphore *sem);
|
2005-04-17 02:20:36 +04:00
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
* trylock for writing -- returns 1 if successful, 0 if contention
|
|
|
|
|
*/
|
2006-07-03 11:24:53 +04:00
|
|
|
extern int down_write_trylock(struct rw_semaphore *sem);
|
2005-04-17 02:20:36 +04:00
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
* release a read lock
|
|
|
|
|
*/
|
2006-07-03 11:24:53 +04:00
|
|
|
extern void up_read(struct rw_semaphore *sem);
|
2005-04-17 02:20:36 +04:00
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
* release a write lock
|
|
|
|
|
*/
|
2006-07-03 11:24:53 +04:00
|
|
|
extern void up_write(struct rw_semaphore *sem);
|
2005-04-17 02:20:36 +04:00
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
* downgrade write lock to read lock
|
|
|
|
|
*/
|
2006-07-03 11:24:53 +04:00
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extern void downgrade_write(struct rw_semaphore *sem);
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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/*
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2006-07-10 15:44:02 +04:00
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* nested locking. NOTE: rwsems are not allowed to recurse
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* (which occurs if the same task tries to acquire the same
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* lock instance multiple times), but multiple locks of the
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* same lock class might be taken, if the order of the locks
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* is always the same. This ordering rule can be expressed
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* to lockdep via the _nested() APIs, but enumerating the
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* subclasses that are used. (If the nesting relationship is
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* static then another method for expressing nested locking is
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* the explicit definition of lock class keys and the use of
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* lockdep_set_class() at lock initialization time.
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2019-04-10 14:32:41 +03:00
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* See Documentation/locking/lockdep-design.rst for more details.)
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2006-07-03 11:24:53 +04:00
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*/
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extern void down_read_nested(struct rw_semaphore *sem, int subclass);
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extern void down_write_nested(struct rw_semaphore *sem, int subclass);
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2016-05-26 07:04:58 +03:00
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extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass);
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2013-01-12 02:31:56 +04:00
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extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
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# define down_write_nest_lock(sem, nest_lock) \
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do { \
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typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
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_down_write_nest_lock(sem, &(nest_lock)->dep_map); \
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} while (0);
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2011-09-22 08:43:05 +04:00
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/*
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* Take/release a lock when not the owner will release it.
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*
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* [ This API should be avoided as much as possible - the
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* proper abstraction for this case is completions. ]
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*/
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extern void down_read_non_owner(struct rw_semaphore *sem);
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extern void up_read_non_owner(struct rw_semaphore *sem);
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2006-07-03 11:24:53 +04:00
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#else
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# define down_read_nested(sem, subclass) down_read(sem)
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2013-01-15 23:12:37 +04:00
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# define down_write_nest_lock(sem, nest_lock) down_write(sem)
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2006-07-03 11:24:53 +04:00
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# define down_write_nested(sem, subclass) down_write(sem)
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2016-05-26 07:04:58 +03:00
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# define down_write_killable_nested(sem, subclass) down_write_killable(sem)
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2011-09-22 08:43:05 +04:00
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# define down_read_non_owner(sem) down_read(sem)
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# define up_read_non_owner(sem) up_read(sem)
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2006-07-03 11:24:53 +04:00
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#endif
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2005-04-17 02:20:36 +04:00
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#endif /* _LINUX_RWSEM_H */
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