Re: PostgreSQL pgbench performance regression in 2.6.23+

Mike Galbraith
2008-05-22T13:17:11Z

On Thu, 2008-05-22 at 14:24 +0200, Peter Zijlstra wrote:
> On Thu, 2008-05-22 at 14:09 +0200, Mike Galbraith wrote:
> > On Thu, 2008-05-22 at 13:44 +0200, Peter Zijlstra wrote:
> >
> > > Humm,.. how to fix this.. we'd need to somehow detect the 1:n nature of
> > > its operation - I'm sure there are other scenarios that could benefit
> > > from this.
> >
> > Maybe simple (minded): cache waker's last non-interrupt context wakee,
> > if the wakee != cached, ignore SYNC_WAKEUP unless sync was requested at
> > call time?
>
> Yeah, something like so - or perhaps like you say cache the wakee.
>
> I picked the wake_affine() condition, because I think that is the
> biggest factor in this behaviour. You could of course also disable all
> of sync.

Works fine (modulo booboo).

-Mike

> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index c86c5c5..856c2a8 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -950,6 +950,8 @@ struct sched_entity {
> u64 last_wakeup;
> u64 avg_overlap;
>
> + struct sched_entity *waker;
> +
> #ifdef CONFIG_SCHEDSTATS
> u64 wait_start;
> u64 wait_max;
> diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> index 894a702..8971044 100644
> --- a/kernel/sched_fair.c
> +++ b/kernel/sched_fair.c
> @@ -1036,7 +1036,8 @@ wake_affine(struct rq *rq, struct sched_domain *this_sd, struct rq *this_rq,
> * a reasonable amount of time then attract this newly
> * woken task:
> */
> - if (sync && curr->sched_class == &fair_sched_class) {
> + if (sync && curr->sched_class == &fair_sched_class &&
> + p->se.waker == curr->se->waker) {
> if (curr->se.avg_overlap < sysctl_sched_migration_cost &&
> p->se.avg_overlap < sysctl_sched_migration_cost)
> return 1;
> @@ -1210,6 +1211,7 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p)
> if (unlikely(se == pse))
> return;
>
> + se->waker = pse;
> cfs_rq_of(pse)->next = pse;
>
> /*
>
>