diff options
| author | Waiman Long <longman@redhat.com> | 2018-10-18 21:45:17 -0400 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2018-10-19 07:53:17 +0200 |
| commit | 9506a7425b094d2f1d9c877ed5a78f416669269b (patch) | |
| tree | 7eacd4d0a4dcc8ffffd2384d9e75624bbbe86e86 /kernel/locking | |
| parent | 0fa809ca7f81c47bea6706bc689e941eb25d7e89 (diff) | |
| download | linux-9506a7425b094d2f1d9c877ed5a78f416669269b.tar.bz2 | |
locking/lockdep: Fix debug_locks off performance problem
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>
Diffstat (limited to 'kernel/locking')
| -rw-r--r-- | kernel/locking/lockdep.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index be76f476c63f..1efada2dd9dd 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -4066,7 +4066,7 @@ void lock_contended(struct lockdep_map *lock, unsigned long ip) { unsigned long flags; - if (unlikely(!lock_stat)) + if (unlikely(!lock_stat || !debug_locks)) return; if (unlikely(current->lockdep_recursion)) @@ -4086,7 +4086,7 @@ void lock_acquired(struct lockdep_map *lock, unsigned long ip) { unsigned long flags; - if (unlikely(!lock_stat)) + if (unlikely(!lock_stat || !debug_locks)) return; if (unlikely(current->lockdep_recursion)) |