linux-kernel - Re: [LNG] Re: [Query] Ticks happen in pair for NO_HZ

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Message-ID: <20140107084734.GP30183@twins.programming.kicks-ass.net>
Date:	Tue, 7 Jan 2014 09:47:34 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Kevin Hilman <khilman@...aro.org>, Ingo Molnar <mingo@...hat.com>,
	Tejun Heo <tj@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Linaro Networking <linaro-networking@...aro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [LNG] Re: [Query] Ticks happen in pair for NO_HZ_FULL cores ?

On Mon, Dec 23, 2013 at 01:48:02PM +0530, Viresh Kumar wrote:
> *But wouldn't it make sense if we can tell scheduler that don't queue
> these works on a CPU that is running in NO_HZ_FULL mode?*

No,.. that's the wrong way around.

> Also any suggestions on how to get rid of __prandom_timer events on
> such CPUs?

That looks to be a normal unpinned timer, it should migrate to a 'busy'
cpu once the one its running on it going idle.

ISTR people trying to make that active and also migrating on nohz full
or somesuch, just like the workqueues. Forgot what happened with that;
if it got dropped it should probably be ressurected.
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