linux-kernel - Re: [PATCH] base: power: domain: Replace mdelay with msleep

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Date:   Mon, 12 Feb 2018 13:40:52 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Lucas Stach <l.stach@...gutronix.de>
Cc:     Jia-Ju Bai <baijiaju1990@...il.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] base: power: domain: Replace mdelay with msleep

On 12 February 2018 at 11:38, Lucas Stach <l.stach@...gutronix.de> wrote:
> Am Freitag, den 09.02.2018, 14:58 +0100 schrieb Ulf Hansson:
>> On 26 January 2018 at 09:38, Jia-Ju Bai <baijiaju1990@...il.com>
>> wrote:
>> > After checking all possible call chains to genpd_dev_pm_detach()
>> > and
>> > genpd_dev_pm_attach() here,
>> > my tool finds that these functions are never called in atomic
>> > context,
>> > namely never in an interrupt handler or holding a spinlock.
>> > Thus mdelay can be replaced with msleep to avoid busy wait.
>> >
>> > This is found by a static analysis tool named DCNS written by
>> > myself.
>> >
>> > Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
>> > ---
>> >  drivers/base/power/domain.c |    4 ++--
>> >  1 file changed, 2 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/drivers/base/power/domain.c
>> > b/drivers/base/power/domain.c
>> > index 0c80bea..f84ac72 100644
>> > --- a/drivers/base/power/domain.c
>> > +++ b/drivers/base/power/domain.c
>> > @@ -2144,7 +2144,7 @@ static void genpd_dev_pm_detach(struct device
>> > *dev, bool power_off)
>> >                 if (ret != -EAGAIN)
>> >                         break;
>> >
>> > -               mdelay(i);
>> > +               msleep(i);
>>
>> This looks like a nice improvement, however moving to msleep() makes
>> the call to cond_resched() below a bit superfluous. Perhaps remove
>> that as well.
>
> At least for small values of i, msleep also has a high chance to
> overshoot the desired sleep by a lot. It would be better to convert
> them to usleep_range with an acceptable slack.

Ack!

[...]

Kind regards
Uffe