Messages in this thread Patch in this message | | | Date | Thu, 19 Jan 2017 11:32:34 -0500 | From | "Steven Rostedt (VMware)" <> | Subject | [PATCH] rtmutex: rt_mutex_slowlock() is mostly called as TASK_INTERRUPTIBLE |
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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> --- diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 1ec0f48..8de6288 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1115,7 +1115,7 @@ __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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