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locking/rtmutex: Flip unlikely() branch to likely() in __rt_mutex_slowlock() 

Running my likely/unlikely profiler for 3 weeks on two production
machines, I discovered that the unlikely() test in
__rt_mutex_slowlock() checking if state is TASK_INTERRUPTIBLE is hit
100% of the time, making it a very likely case.

The reason is, on a vanilla kernel, the majority case of calling
rt_mutex() is from the futex code. This code is always called as
TASK_INTERRUPTIBLE. In the -rt patch, this code is commonly called when
PREEMPT_RT is enabled with TASK_UNINTERRUPTIBLE. But that's not the
likely scenario.

The rt_mutex() code should be optimized for the common vanilla case,
and that is from a futex, with TASK_INTERRUPTIBLE as the state.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170119113234.1efeedd1@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Steven Rostedt (VMware) 2017-01-19 11:32:34 -05:00 committed by Ingo Molnar
parent bcc9a76d5a
commit 4009f4b3a9
1 changed files with 1 additions and 1 deletions
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2
kernel/locking/rtmutex.c
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@ -1179,7 +1179,7 @@ __rt_mutex_slowlock(struct rt_mutex *lock, int state,
* TASK_INTERRUPTIBLE checks for signals and
* timeout. Ignored otherwise.
*/
if (unlikely(state == TASK_INTERRUPTIBLE)) {
if (likely(state == TASK_INTERRUPTIBLE)) {
/* Signal pending? */
if (signal_pending(current))
ret = -EINTR;