linux-kernel - Re: [PATCH] PM/runtime: Do not needlessly call ktime

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Message-ID: <CAKfTPtCV=PYAqG=LavafTpMxvXdr7W-bfsOkpP+04EtOaicjyg@mail.gmail.com>
Date:   Thu, 10 Jan 2019 19:56:19 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Ladislav Michl <ladis@...ux-mips.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH] PM/runtime: Do not needlessly call ktime_get

On Thu, 10 Jan 2019 at 10:51, Ladislav Michl <ladis@...ux-mips.org> wrote:
>
> pm_runtime_autosuspend_expiration calls ktime_get even when
> its returned value may be unused. Therefore get current time
> later and remove gotos while there.
>
> Signed-off-by: Ladislav Michl <ladis@...ux-mips.org>

Acked-by: Vincent Guittot <vincent.guittot@...aro.org>

> ---
>  NOTE: Depends on Vincent's "[PATCH v2] PM/runtime: Fix autosuspend_delay
>        on 32bits arch"!
>
>  drivers/base/power/runtime.c | 19 ++++++++-----------
>  1 file changed, 8 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> index 457be03b744d..836b1b8784eb 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -129,24 +129,21 @@ static void pm_runtime_cancel_pending(struct device *dev)
>  u64 pm_runtime_autosuspend_expiration(struct device *dev)
>  {
>         int autosuspend_delay;
> -       u64 last_busy, expires = 0;
> -       u64 now = ktime_to_ns(ktime_get());
> +       u64 expires;
>
>         if (!dev->power.use_autosuspend)
> -               goto out;
> +               return 0;
>
>         autosuspend_delay = READ_ONCE(dev->power.autosuspend_delay);
>         if (autosuspend_delay < 0)
> -               goto out;
> -
> -       last_busy = READ_ONCE(dev->power.last_busy);
> +               return 0;
>
> -       expires = last_busy + (u64)autosuspend_delay * NSEC_PER_MSEC;
> -       if (expires <= now)
> -               expires = 0;    /* Already expired. */
> +       expires  = READ_ONCE(dev->power.last_busy);
> +       expires += (u64)autosuspend_delay * NSEC_PER_MSEC;
> +       if (expires > ktime_to_ns(ktime_get()))
> +               return expires; /* Expires in the future */
>
> - out:
> -       return expires;
> +       return 0;
>  }
>  EXPORT_SYMBOL_GPL(pm_runtime_autosuspend_expiration);
>
> --
> 2.20.1
>