Commit 9f3520c3 authored May 08, 2015 by Yuanhan Liu Committed by NeilBrown Jun 17, 2015

wait: introduce wait_event_exclusive_cmd



It's just a variant of wait_event_cmd(), with exclusive flag being set.

For cases like RAID5, which puts many processes to sleep until 1/4
resources are free, a wake_up wakes up all processes to run, but
there is one process being able to get the resource as it's protected
by a spin lock. That ends up introducing heavy lock contentions, and
hurts performance badly.

Here introduce wait_event_exclusive_cmd to relieve the lock contention
naturally by letting wake_up just wake up one process.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
v2: its assumed that wait*() and __wait*() have the same arguments - peterz

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>

parent 4c9309c0

include/linux/wait.h

+13 −0

Original line number	Diff line number	Diff line
		@@ -358,6 +358,19 @@ do { \
		__ret; \
		})

		#define __wait_event_exclusive_cmd(wq, condition, cmd1, cmd2) \
		(void)___wait_event(wq, condition, TASK_UNINTERRUPTIBLE, 1, 0, \
		cmd1; schedule(); cmd2)
		/*
		* Just like wait_event_cmd(), except it sets exclusive flag
		*/
		#define wait_event_exclusive_cmd(wq, condition, cmd1, cmd2) \
		do { \
		if (condition) \
		break; \
		__wait_event_exclusive_cmd(wq, condition, cmd1, cmd2); \
		} while (0)

		#define __wait_event_cmd(wq, condition, cmd1, cmd2) \
		(void)___wait_event(wq, condition, TASK_UNINTERRUPTIBLE, 0, 0, \
		cmd1; schedule(); cmd2)