linux-kernel - Re: [patch] sched/fair: Move se->vruntime normalization state into struct sched

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Date:	Tue, 24 May 2016 10:04:17 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	peterz@...radead.org
Cc:	umgwanakikbuti@...il.com, mingo@...nel.org,
	linux-kernel@...r.kernel.org, bsegall@...gle.com,
	matt@...eblueprint.co.uk, morten.rasmussen@....com, pjt@...gle.com,
	tglx@...utronix.de, byungchul.park@....com, ahh@...gle.com
Subject: Re: [patch] sched/fair: Move se->vruntime normalization state into
 struct sched_entity

On Mon, May 23, 2016 at 2:19 AM +0200, Peter Zijlstra wrote:
> On Sun, May 22, 2016 at 09:00:01AM +0200, Mike Galbraith wrote:
> > On Sat, 2016-05-21 at 21:00 +0200, Mike Galbraith wrote:
> > > On Sat, 2016-05-21 at 16:04 +0200, Mike Galbraith wrote:
> > >
> > > > Wakees that were not migrated/normalized eat an unwanted min_vruntime,
> > > > and likely take a size XXL latency hit.  Big box running master bled
> > > > profusely under heavy load until I turned TTWU_QUEUE off.
> >
> > May as well make it official and against master.today.  Fly or die
> > little patchlet.
> >
> > sched/fair: Move se->vruntime normalization state into struct sched_entity
> 
> Does this work?

This gets rid of the additional lost wakeups introduced during the
merge window, thank you!

The pre-existing low-probability lost wakeups still persist, sad to say
Can't have everything, I guess.

Tested-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

> ---
>  include/linux/sched.h |  1 +
>  kernel/sched/core.c   | 18 +++++++++++-------
>  2 files changed, 12 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 1b43b45a22b9..a2001e01b3df 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1534,6 +1534,7 @@ struct task_struct {
>         unsigned sched_reset_on_fork:1;
>         unsigned sched_contributes_to_load:1;
>         unsigned sched_migrated:1;
> +       unsigned sched_remote_wakeup:1;
>         unsigned :0; /* force alignment to the next boundary */
> 
>         /* unserialized, strictly 'current' */
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 404c0784b1fc..7f2cae4620c7 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1768,13 +1768,15 @@ void sched_ttwu_pending(void)
>         cookie = lockdep_pin_lock(&rq->lock);
> 
>         while (llist) {
> +               int wake_flags = 0;
> +
>                 p = llist_entry(llist, struct task_struct, wake_entry);
>                 llist = llist_next(llist);
> -               /*
> -                * See ttwu_queue(); we only call ttwu_queue_remote() when
> -                * its a x-cpu wakeup.
> -                */
> -               ttwu_do_activate(rq, p, WF_MIGRATED, cookie);
> +
> +               if (p->sched_remote_wakeup)
> +                       wake_flags = WF_MIGRATED;
> +
> +               ttwu_do_activate(rq, p, wake_flags, cookie);
>         }
> 
>         lockdep_unpin_lock(&rq->lock, cookie);
> @@ -1819,10 +1821,12 @@ void scheduler_ipi(void)
>         irq_exit();
>  }
> 
> -static void ttwu_queue_remote(struct task_struct *p, int cpu)
> +static void ttwu_queue_remote(struct task_struct *p, int cpu, int
> wake_flags)
>  {
>         struct rq *rq = cpu_rq(cpu);
> 
> +       p->sched_remote_wakeup = !!(wake_flags & WF_MIGRATED);
> +
>         if (llist_add(&p->wake_entry, &cpu_rq(cpu)->wake_list)) {
>                 if (!set_nr_if_polling(rq->idle))
>                         smp_send_reschedule(cpu);
> @@ -1869,7 +1873,7 @@ static void ttwu_queue(struct task_struct *p, int
> cpu, int wake_flags)
>  #if defined(CONFIG_SMP)
>         if (sched_feat(TTWU_QUEUE) && !cpus_share_cache(smp_processor_id(),
> cpu)) {
>                 sched_clock_cpu(cpu); /* sync clocks x-cpu */
> -               ttwu_queue_remote(p, cpu);
> +               ttwu_queue_remote(p, cpu, wake_flags);
>                 return;
>         }
>  #endif