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authorSteven Rostedt (VMware) <rostedt@goodmis.org>2017-01-19 11:32:34 -0500
committerIngo Molnar <mingo@kernel.org>2017-01-30 11:42:59 +0100
commit4009f4b3a9d8b74547269f293e6a920adf278996 (patch)
treed89abc6ec739d45d9f24a4684af2275ffa62fced /kernel/locking
parentbcc9a76d5ac426bc45c9e863b1830347827ca77a (diff)
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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>
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/rtmutex.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 2f443ed2320a..d340be3a488f 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -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;
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