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wait: introduce wait_event_exclusive_cmd

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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>
This commit is contained in:
Yuanhan Liu 2015-05-08 18:19:05 +10:00 committed by NeilBrown
parent 4c9309c0cc
commit 9f3520c311
1 changed files with 13 additions and 0 deletions
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13
include/linux/wait.h
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@ -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)