linux-kernel - Re: [PATCH v3 0/5] Improve newidle lb cost tracking and early abort

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Date:   Sun, 31 Oct 2021 11:18:04 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/5] Improve newidle lb cost tracking and early abort

On Fri, 29 Oct 2021 at 19:00, Tim Chen <tim.c.chen@...ux.intel.com> wrote:
>
> On Wed, 2021-10-27 at 10:49 +0200, Vincent Guittot wrote:
> >
> >
> > Few problems still remain in your case if I'm not wrong:
> > There is a patch that ensures that rq->next_balance is never set in
> > the past.
> >
>
> Vincent,
>
> Were you planning to take the patch to prevent the next_balance to be
> in the past?

I can add it to this serie


>
> Tim
>
> ---
> From 2a5ebdeabbfdf4584532ef0e27d37ed75ca7dbd3 Mon Sep 17 00:00:00 2001
> From: Tim Chen <tim.c.chen@...ux.intel.com>
> Date: Tue, 11 May 2021 09:55:41 -0700
> Subject: [PATCH] sched: sched: Fix rq->next_balance time updated to earlier
>  than current time
> To: hmem@...ists.intel.com
>
> In traces on newidle_balance(), this_rq->next_balance
> time goes backward and earlier than current time jiffies, e.g.
>
> 11.602 (         ): probe:newidle_balance:(ffffffff810d2470) this_rq=0xffff88fe7f8aae00 next_balance=0x1004fb76c jiffies=0x1004fb739
> 11.624 (         ): probe:newidle_balance:(ffffffff810d2470) this_rq=0xffff88fe7f8aae00 next_balance=0x1004fb731 jiffies=0x1004fb739
> 13.856 (         ): probe:newidle_balance:(ffffffff810d2470) this_rq=0xffff88fe7f8aae00 next_balance=0x1004fb76c jiffies=0x1004fb73b
> 13.910 (         ): probe:newidle_balance:(ffffffff810d2470) this_rq=0xffff88fe7f8aae00 next_balance=0x1004fb731 jiffies=0x1004fb73b
> 14.637 (         ): probe:newidle_balance:(ffffffff810d2470) this_rq=0xffff88fe7f8aae00 next_balance=0x1004fb76c jiffies=0x1004fb73c
> 14.666 (         ): probe:newidle_balance:(ffffffff810d2470) this_rq=0xffff88fe7f8aae00 next_balance=0x1004fb731 jiffies=0x1004fb73c
>
> It doesn't make sense to have a next_balance in the past.
> Fix newidle_balance() and update_next_balance() so the next
> balance time is at least jiffies+1.
> ---
>  kernel/sched/fair.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1d75af1ecfb4..740a0572cbf1 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9901,7 +9901,10 @@ update_next_balance(struct sched_domain *sd, unsigned long *next_balance)
>
>         /* used by idle balance, so cpu_busy = 0 */
>         interval = get_sd_balance_interval(sd, 0);
> -       next = sd->last_balance + interval;
> +       if (time_after(jiffies+1, sd->last_balance + interval))
> +               next = jiffies+1;
> +       else
> +               next = sd->last_balance + interval;
>
>         if (time_after(*next_balance, next))
>                 *next_balance = next;
> @@ -10681,6 +10684,8 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
>
>  out:
>         /* Move the next balance forward */
> +       if (time_after(jiffies+1, this_rq->next_balance))
> +               this_rq->next_balance = jiffies+1;
>         if (time_after(this_rq->next_balance, next_balance))
>                 this_rq->next_balance = next_balance;
>
> --
> 2.20.1
>
>