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_cmd_exclusive to relieve the lock contention
naturally by letting wake_up() just wake up one process.
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Yuanhan Liu <yuanhan.liu@xxxxxxxxxxxxxxx>
---
include/linux/wait.h | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/include/linux/wait.h b/include/linux/wait.h
index 2db8334..6c3b4de 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -358,10 +358,18 @@ do { \
__ret; \
})
-#define __wait_event_cmd(wq, condition, cmd1, cmd2) \
- (void)___wait_event(wq, condition, TASK_UNINTERRUPTIBLE, 0, 0, \
+#define __wait_event_cmd(wq, condition, cmd1, cmd2, exclusive) \
+ (void)___wait_event(wq, condition, TASK_UNINTERRUPTIBLE, exclusive, 0, \
cmd1; schedule(); cmd2)
+
+#define wait_event_cmd_exclusive(wq, condition, cmd1, cmd2) \
+do { \
+ if (condition) \
+ break; \
+ __wait_event_cmd(wq, condition, cmd1, cmd2, 1); \
+} while (0)
+
/**
* wait_event_cmd - sleep until a condition gets true
* @wq: the waitqueue to wait on
@@ -380,7 +388,7 @@ do { \
do { \
if (condition) \
break; \
- __wait_event_cmd(wq, condition, cmd1, cmd2); \
+ __wait_event_cmd(wq, condition, cmd1, cmd2, 0); \
} while (0)
#define __wait_event_interruptible(wq, condition) \
--
1.9.0
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