Commit afffc6c1 authored Feb 01, 2015 by Davidlohr Bueso Committed by Ingo Molnar Feb 04, 2015

locking/rtmutex: Optimize setting task running after being blocked



We explicitly mark the task running after returning from
a __rt_mutex_slowlock() call, which does the actual sleeping
via wait-wake-trylocking. As such, this patch does two things:

(1) refactors the code so that setting current to TASK_RUNNING
    is done by __rt_mutex_slowlock(), and not by the callers. The
    downside to this is that it becomes a bit unclear when at what
    point we block. As such I've added a comment that the task
    blocks when calling __rt_mutex_slowlock() so readers can figure
    out when it is running again.

(2) relaxes setting current's state through __set_current_state(),
    instead of it's more expensive barrier alternative. There was no
    need for the implied barrier as we're obviously not planning on
    blocking.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1422857784.18096.1.camel@stgolabs.net


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 73105994

kernel/locking/rtmutex.c

+3 −4

Original line number	Diff line number	Diff line
		@@ -1130,6 +1130,7 @@ __rt_mutex_slowlock(struct rt_mutex *lock, int state,
		set_current_state(state);
		}

		__set_current_state(TASK_RUNNING);
		return ret;
		}

		@@ -1188,10 +1189,9 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
		ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);

		if (likely(!ret))
		/* sleep on the mutex */
		ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);

		set_current_state(TASK_RUNNING);

		if (unlikely(ret)) {
		remove_waiter(lock, &waiter);
		rt_mutex_handle_deadlock(ret, chwalk, &waiter);
		@@ -1626,10 +1626,9 @@ int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,

		set_current_state(TASK_INTERRUPTIBLE);

		/* sleep on the mutex */
		ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);

		set_current_state(TASK_RUNNING);

		if (unlikely(ret))
		remove_waiter(lock, waiter);