On Thu, Aug 07, 2014 at 02:16:16PM -0400, Rik van Riel wrote:
> On 08/07/2014 06:53 AM, Fengguang Wu wrote:
> > Hi Rik,
> >
> > We noticed the below performance regression in commit
> > 096aa33863a5e48de52d2ff30e0801b7487944f4 ("sched/numa: Decay
> > ->wakee_flips instead of zeroing")
> >
> > b1ad065e65f5610 096aa33863a5e48de52d2ff30 testbox/testcase/testparams
> > --------------- ------------------------- ---------------------------
> > 122361 ± 0% -21.4% 96140 ± 0%
> > lkp-snb01/hackbench/50%-process-pipe
> > 122361 ± 0% -21.4% 96140 ± 0% TOTAL hackbench.throughput
>
> I guess the performance of that benchmark depends on it
> "slipping under the wire" after each time the kernel
> zeroes out ->wakee_flips.
>
> Depending on repeatedly pulling the wakee back to the same
> node as the waker suggests something else in the kernel may
> be pulling the wakee to another place in the system repeatedly,
> as well, just at a lower frequency (load balancer?).
>
> I have also noticed that select_idle_sibling often fails to
> find an idle sibling within the LLC domain, even when it
> exists. Fixing that bug sometimes results in lower performance.
>
> It appears that some of the performance results of the scheduler
> appear on the code acting in an opposite way to its documented
> intention.
>
> It may be best to revert 096aa33863a for now...
Does something like so cure anything? Is that a 'normal' hackbench run?
lemme see if I can reproduce on anything.
---
kernel/sched/fair.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bfa3c86d0d68..13f00daf8028 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4098,14 +4098,19 @@ static unsigned long cpu_avg_load_per_task(int cpu)
static void record_wakee(struct task_struct *p)
{
+ unsigned long now = jiffies;
/*
* Rough decay (wiping) for cost saving, don't worry
* about the boundary, really active task won't care
* about the loss.
*/
- if (time_after(jiffies, current->wakee_flip_decay_ts + HZ)) {
+ if (time_after(now, current->wakee_flip_decay_ts + BITS_PER_LONG * HZ))
{
+ current->wakee_flips = 0;
+ current->wakee_flip_decay_ts = now;
+ } else while (time_after(now, current->wakee_flip_decay_ts + HZ) &&
+ current->wakee_flips) {
current->wakee_flips >>= 1;
- current->wakee_flip_decay_ts = jiffies;
+ current->wakee_flip_decay_ts += HZ;
}
if (current->last_wakee != p) {
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