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

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Date:   Mon, 12 Feb 2018 11:38:13 +0100
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Ulf Hansson <ulf.hansson@...aro.org>,
        Jia-Ju Bai <baijiaju1990@...il.com>
Cc:     "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

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.

Regards,
Lucas

> >                 cond_resched();
> >         }
> > 
> > @@ -2231,7 +2231,7 @@ int genpd_dev_pm_attach(struct device *dev)
> >                 if (ret != -EAGAIN)
> >                         break;
> > 
> > -               mdelay(i);
> > +               msleep(i);
> 
> Ditto.
> 
> >                 cond_resched();
> >         }
> >         mutex_unlock(&gpd_list_lock);
> > --
> > 1.7.9.5
> > 
> 
> Kind regards
> Uffe