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From: Davidlohr Bueso <dave@stgolabs.net>
To: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org, Davidlohr Bueso <dave@stgolabs.net>
Subject: [PATCH] locking/rtmutex: Optimize setting task running after being blocked
Date: Sun, 01 Feb 2015 22:16:24 -0800	[thread overview]
Message-ID: <1422857784.18096.1.camel@stgolabs.net> (raw)

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>
---
 kernel/locking/rtmutex.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 7c98873..3059bc2f 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -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);
 
-- 
2.1.4




             reply	other threads:[~2015-02-02  6:16 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-02-02  6:16 Davidlohr Bueso [this message]
2015-02-04 14:38 ` [tip:locking/core] " tip-bot for Davidlohr Bueso

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