linux-kernel - Re: [PATCH 5/8] nohz: Restart the tick from irq exit

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Message-ID: <557D4714.1090600@linux.vnet.ibm.com>
Date:	Sun, 14 Jun 2015 14:49:16 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Lameter <cl@...ux.com>,
	Ingo Molnar <mingo@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 5/8] nohz: Restart the tick from irq exit

On 06/11/2015 11:06 PM, Frederic Weisbecker wrote:
> Restart the tick when necessary from the irq exit path. It makes nohz
> full more flexible and allow it to piggyback the tick restart on the
> scheduler IPI in the future instead of sending a dedicated IPI that
> often doubles the scheduler IPI on task wakeup. This will require

You can piggy back on the scheduler ipi when you add a timer/hrtimer and
add a new task to the runqueue of the nohz_full cpus, since we call
resched_curr() in these code paths. But what about the calls to kick
nohz_full cpus by perf events and posix cpu timers ? These call sites
seem to be concerned about specifically waking up nohz_full cpus as far
as I can see. IOW there is no scheduling ipi that we can fall back on in
these paths.

> careful review of resched_curr() callers.
> 

Regards
Preeti U Murthy

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