diff options
| author | Waiman Long <longman@redhat.com> | 2018-10-18 21:45:17 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-11-21 09:27:31 +0100 |
| commit | ef42ef8451faae09fe3a0b00c603ceeda8f5f5c5 (patch) | |
| tree | 903568a66cf47afbf07337323d8d91c73f0d8f09 /lib/debug_locks.c | |
| parent | 049b96e8c5d0e50ce9ebefe5206d1f3032a958ef (diff) | |
locking/lockdep: Fix debug_locks off performance problem
[ Upstream commit 9506a7425b094d2f1d9c877ed5a78f416669269b ]
It was found that when debug_locks was turned off because of a problem
found by the lockdep code, the system performance could drop quite
significantly when the lock_stat code was also configured into the
kernel. For instance, parallel kernel build time on a 4-socket x86-64
server nearly doubled.
Further analysis into the cause of the slowdown traced back to the
frequent call to debug_locks_off() from the __lock_acquired() function
probably due to some inconsistent lockdep states with debug_locks
off. The debug_locks_off() function did an unconditional atomic xchg
to write a 0 value into debug_locks which had already been set to 0.
This led to severe cacheline contention in the cacheline that held
debug_locks. As debug_locks is being referenced in quite a few different
places in the kernel, this greatly slow down the system performance.
To prevent that trashing of debug_locks cacheline, lock_acquired()
and lock_contended() now checks the state of debug_locks before
proceeding. The debug_locks_off() function is also modified to check
debug_locks before calling __debug_locks_off().
Signed-off-by: Waiman Long <longman@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/1539913518-15598-1-git-send-email-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'lib/debug_locks.c')
| -rw-r--r-- | lib/debug_locks.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/lib/debug_locks.c b/lib/debug_locks.c index 96c4c633d95e..124fdf238b3d 100644 --- a/lib/debug_locks.c +++ b/lib/debug_locks.c @@ -37,7 +37,7 @@ EXPORT_SYMBOL_GPL(debug_locks_silent); */ int debug_locks_off(void) { - if (__debug_locks_off()) { + if (debug_locks && __debug_locks_off()) { if (!debug_locks_silent) { console_verbose(); return 1; |