linux-kernel - Re: [PATCH] timer: Make msleep(0) a nop

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Message-ID: <CALAqxLUMj4xFV+RAVstLzAO3mDn=m0UwSSuxUTmOJWVdM6-ELg@mail.gmail.com>
Date:	Wed, 17 Aug 2016 12:39:23 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] timer: Make msleep(0) a nop

On Fri, Aug 12, 2016 at 1:40 AM,  <ville.syrjala@...ux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@...ux.intel.com>
>
> Thanks to the msecs_to_jiffies()+1 msleep(0) may actually sleep for up
> to one jiffy. Presumably the caller should be satisfied if we "sleep"
> for 0 jiffies instead of 0-1 jiffies, so let's just turn msleep(0)
> into a nop.
>
> This can simplify some callers as they don't have to check for the
> 0 msecs case themselves anymore. Or if they're not checking for 0,
> they might avoid a needless sleep occasionally.
>
> A slight concern might be that someone is calling msleep(0) and
> depending on some delay being there. But that can clearly blow up
> even without this change, so I'm not overly worried about it.

I think this is more then a slight concern. Calls to *sleep() make
sure to sleep for at least the amount of time specified, but there is
no upper bound on how long that sleep might actually be. So msleep(0)
sleeping for 1 jiffy or more is correct. And when folks want the
minimum sleep granularity, msleep(0) is a valid way to get that.

So I don't think this is a good idea to change, at least w/o a much
stronger rational.

thanks
-john