sched: Fix load balancing performance regression in should_we_balance()
Commit 23f0d20 ("sched: Factor out code to should_we_balance()")
introduces the should_we_balance() function. This function should
return 1 if this cpu is appropriate for balancing. But the newly
introduced code doesn't do so, it returns 0 instead of 1.
This introduces performance regression, reported by Dave Chinner:
v4 filesystem v5 filesystem
3.11+xfsdev: 220k files/s 225k files/s
3.12-git 180k files/s 185k files/s
3.12-git-revert 245k files/s 247k files/s
You can find more detailed information at:
https://lkml.org/lkml/2013/9/10/1
This patch corrects the return value of should_we_balance()
function as orignally intended.
With this patch, Dave Chinner reports that the regression is gone:
v4 filesystem v5 filesystem
3.11+xfsdev: 220k files/s 225k files/s
3.12-git 180k files/s 185k files/s
3.12-git-revert 245k files/s 247k files/s
3.12-git-fix 249k files/s 248k files/s
Reported-by: Dave Chinner <dchinner@redhat.com>
Tested-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>
Link: http://lkml.kernel.org/r/20130910065448.GA20368@lge.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7f0a5e6..9b3fe1c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5151,7 +5151,7 @@
* First idle cpu or the first cpu(busiest) in this sched group
* is eligible for doing load balancing at this and above domains.
*/
- return balance_cpu != env->dst_cpu;
+ return balance_cpu == env->dst_cpu;
}
/*
