linux-kernel - Re: [GIT PULL] nohz: Fix double clock write on idle ticks

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Date:	Sun, 24 Aug 2014 12:07:34 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Subject: Re: [GIT PULL] nohz: Fix double clock write on idle ticks

* Frederic Weisbecker <fweisbec@...il.com> wrote:

> From: Frederic Weisbecker <fweisbec@...il.com>
> 
> Ingo,
> 
> Please pull the nohz/drop-double-write-v3 branch that can be found at:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> 	nohz/drop-double-write-v3
> 
> Although the 1st patch fixes a bug, it was a longstanding issue so
> that branch doesn't need to be applied in 3.17. The next merge window
> looks better.
> 
> --
> The tick reschedules itself unconditionally. It's relevant in periodic
> mode but not in dynticks mode where it results in spurious double clock
> writes and even spurious periodic behaviour for low-res case.
> 
> This set fixes that:
> 
> * 1st patch removes low-res periodic tick rescheduling in nohz mode.
> This fixes spurious periodic behaviour.
> 
> * 2nd patch does the same for high-res mode. Here there is no such
> spurious periodic behaviour but it still spares a double clock write
> in some cases.
> ---
> 
> 
> Thanks,
> 	Frederic
> ---
> 
> Viresh Kumar (2):
>       nohz: Fix spurious periodic tick behaviour in low-res dynticks mode
>       nohz: Avoid tick's double reprogramming in highres mode
> 
> 
>  kernel/time/tick-sched.c | 8 ++++++++
>  1 file changed, 8 insertions(+)

These fixes are pretty small - any objections against putting it into
timers/urgent and including it in v3.17?

Thanks,

	Ingo
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