linux-kernel - Re: [RFC PATCH v2 3/3] sched: introduce synchronized idle injection

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Message-ID: <20151110091408.5e31366c@icelake>
Date:	Tue, 10 Nov 2015 09:14:08 -0800
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>,
	Len Brown <len.brown@...el.com>,
	Andi Kleen <andi.kleen@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Eduardo Valentin <edubezval@...il.com>,
	Punit Agrawal <punit.agrawal@....com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	jacob.jun.pan@...ux.intel.com
Subject: Re: [RFC PATCH v2 3/3] sched: introduce synchronized idle injection

On Tue, 10 Nov 2015 18:00:10 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> > Different per CPU timer may intercept parameter changes at slightly
> > different time, so there is a race condition such that some CPUs may
> > catch the period change later by one period, which results in a
> > correct period change but at a different time, i.e. out of sync.  
> 
> Ah yes. So if the locking hurts I can come up with a lockless
> algorithm for this. Shouldn't be too hard.
Great! the current patch was designed to be lockless but a
little awkward. My idea was to have a common start time, then we don't
need to worry about CPUs out of sync, at most they will be off by one
period then catch up.

Thanks,

Jacob
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