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Date: Tue, 10 Nov 2015 08:50:55 -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 17:36:46 +0100 Peter Zijlstra <peterz@...radead.org> wrote: > > The downside is that we need to restart the timers every time if > > user were to change injection parameters, i.e. duration and percent. > > Or do locking which might be too expensive. In the previous > > approach, it will naturally catch up the parameter change. > > Why? the timer will fire and observe the new value for reprogramming > the next period. All you need to do is to ensure whole values are > written/read -- ie. avoid load/store tearing. 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. Jacob -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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