linux-kernel - Re: [PATCH v6 1/2] PM-runtime: update accounting

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Date:   Tue, 22 Jan 2019 16:13:51 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH v6 1/2] PM-runtime: update accounting_timestamp only when enable

On Tue, Jan 22, 2019 at 3:24 PM Vincent Guittot
<vincent.guittot@...aro.org> wrote:
>
> Initializing accounting_timestamp to something different from 0 during
> pm_runtime_init() doesn't make sense and put useless ordering constraint between
> timekeeping_init() and pm_runtime_init().
> PM runtime should start accounting time only when it is enable and discard
> the period when disabled.
> Set accounting_timestamp to now when enabling PM runtime.
>
> Suggested-by: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---
>  drivers/base/power/runtime.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> index fb5e2b6..7df1d05 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -1306,6 +1306,10 @@ void pm_runtime_enable(struct device *dev)
>
>         spin_lock_irqsave(&dev->power.lock, flags);
>
> +       /* About to enable runtime pm, set accounting_timestamp to now */
> +       if (dev->power.disable_depth == 1)
> +               dev->power.accounting_timestamp = jiffies;

I would do this in the dev->power.disable_depth > 0 branch below.
Just check if disable_depth is zero after decrementing it and update
accounting_timestamp if so.

> +
>         if (dev->power.disable_depth > 0)
>                 dev->power.disable_depth--;
>         else
> @@ -1506,7 +1510,7 @@ void pm_runtime_init(struct device *dev)
>         dev->power.request_pending = false;
>         dev->power.request = RPM_REQ_NONE;
>         dev->power.deferred_resume = false;
> -       dev->power.accounting_timestamp = jiffies;
> +       dev->power.accounting_timestamp = 0;
>         INIT_WORK(&dev->power.work, pm_runtime_work);
>
>         dev->power.timer_expires = 0;
> --
> 2.7.4
>