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@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
v2: its assumed that wait*() and __wait*() have the same arguments - peterz
Signed-off-by: Yuanhan Liu <yuanhan.liu@xxxxxxxxxxxxxxx>
---
include/linux/wait.h | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/include/linux/wait.h b/include/linux/wait.h
index 2db8334..db78c72 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -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)
--
1.9.0
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