linux-kernel - Re: [RFC PATCH v2 4/8] tick/nohz: keep tick on for a fast idle

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Message-ID: <1508135135.8087.17.camel@gmx.de>
Date:   Mon, 16 Oct 2017 08:25:35 +0200
From:   Mike Galbraith <efault@....de>
To:     "Li, Aubrey" <aubrey.li@...ux.intel.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Aubrey Li <aubrey.li@...el.com>
Cc:     tglx@...utronix.de, peterz@...radead.org, len.brown@...el.com,
        ak@...ux.intel.com, tim.c.chen@...ux.intel.com,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 4/8] tick/nohz: keep tick on for a fast idle

On Mon, 2017-10-16 at 13:34 +0800, Li, Aubrey wrote:
> On 2017/10/16 12:45, Mike Galbraith wrote:
> > On Mon, 2017-10-16 at 11:26 +0800, Li, Aubrey wrote:
> >>
> >> I'll try to move quiet_vmstat() into the normal idle branch if this patch series
> >> are reasonable. Is fast_idle a good indication for it?
> > 
> > see x86_tip 62cb1188ed86 sched/idle: Move quiet_vmstate() into the NOHZ code
> 
> It looks like this commit makes tick stop critical as it can be invoked in interrupt
> exit path?

do_idle() ain't critical?  It is in my book.  Hopefully, you're about
to make that idle_stat.fast_idle thingy liberal enough that we cease
mucking about with the tick on every microscopic idle (and I can then
trash my years old local patch to avoid needlessly eating that cost).

	-Mike