linux-kernel - Re: [PATCH] PM/runtime: Optimize pm_runtime_autosuspend

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Date:   Wed, 06 Feb 2019 11:34:03 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
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>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Biju Das <biju.das@...renesas.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH] PM/runtime: Optimize pm_runtime_autosuspend_expiration()

On Wednesday, January 30, 2019 10:40:17 PM CET Ladislav Michl wrote:
> pm_runtime_autosuspend_expiration calls ktime_get_mono_fast_ns
> 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: Tony Lindgren <tony@...mide.com>
> Acked-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---
>  This patch is based on top of bleeding-edge branch, where
>  "[PATCH v2 ] PM-runtime: fix deadlock with ktime" is sitting.
>  I expect v3 of that patch, which should not harm this one.
>  It is meant to replace "PM/runtime: Do not needlessly call ktime_get"
>  sent earlier.
> 
>  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 65e2b5f48e0c..7bbe28faca8d 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -145,24 +145,21 @@ 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_get_mono_fast_ns();
> +	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_get_mono_fast_ns())
> +		return expires;	/* Expires in the future */
>  
> - out:
> -	return expires;
> +	return 0;
>  }
>  EXPORT_SYMBOL_GPL(pm_runtime_autosuspend_expiration);
>  
> 

Applied, thanks!