Re: [RFCv5 PATCH 11/46] sched: Remove blocked load and utilization contributions of dying tasks

Morten Rasmussen
2015-07-22T13:42:32Z

On Wed, Jul 22, 2015 at 02:51:01PM +0800, Leo Yan wrote:
> On Tue, Jul 07, 2015 at 07:23:54PM +0100, Morten Rasmussen wrote:
> > Tasks being dequeued for the last time (state == TASK_DEAD) are dequeued
> > with the DEQUEUE_SLEEP flag which causes their load and utilization
> > contributions to be added to the runqueue blocked load and utilization.
> > Hence they will contain load or utilization that is gone away. The issue
> > only exists for the root cfs_rq as cgroup_exit() doesn't set
> > DEQUEUE_SLEEP for task group exits.
> >
> > If runnable+blocked load is to be used as a better estimate for cpu
> > load the dead task contributions need to be removed to prevent
> > load_balance() (idle_balance() in particular) from over-estimating the
> > cpu load.
> >
> > 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 | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 775b0c7..fa12ce5 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -3217,6 +3217,8 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
> > * Update run-time statistics of the 'current'.
> > */
> > update_curr(cfs_rq);
> > + if (entity_is_task(se) && task_of(se)->state == TASK_DEAD)
> > + flags &= !DEQUEUE_SLEEP;
>
> So flags will be set to zero? Could be replaced by "flags &= ~DEQUEUE_SLEEP"?

Not could, should :)

I meant to clear the flag, but used the wrong operator. We only have
DEQUEUE_SLEEP and 0 at the moment so it doesn't matter, but it might
later.

Thanks,
Morten