[PATCH 03/16] sched/fair: Disregard idle task wakee_flips in wake_wide

Morten Rasmussen
2016-05-23T10:58:32Z

wake_wide() is based on task wakee_flips of the waker and the wakee to
decide whether an affine wakeup is desirable. On lightly loaded systems
the waker is frequently the idle task (pid=0) which can accumulate a lot
of wakee_flips in that scenario. It makes little sense to prevent affine
wakeups on an idle cpu due to the idle task wakee_flips, so it makes
more sense to ignore them in wake_wide().

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>

Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
---
kernel/sched/fair.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c49e25a..0fe3020 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5007,6 +5007,10 @@ static int wake_wide(struct task_struct *p)
unsigned int slave = p->wakee_flips;
int factor = this_cpu_read(sd_llc_size);

+ /* Don't let the idle task prevent affine wakeups */
+ if (is_idle_task(current))
+ return 0;
+
if (master < slave)
swap(master, slave);
if (slave < factor || master < slave * factor)
--
1.9.1