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Date: Wed, 18 Nov 2015 13:49:46 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Morten Rasmussen <morten.rasmussen@....com> Cc: Ingo Molnar <mingo@...nel.org>, Jacob Pan <jacob.jun.pan@...ux.intel.com>, Ingo Molnar <mingo@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, John Stultz <john.stultz@...aro.org>, LKML <linux-kernel@...r.kernel.org>, Arjan van de Ven <arjan@...ux.intel.com>, Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>, Len Brown <len.brown@...el.com>, Rafael Wysocki <rafael.j.wysocki@...el.com>, Eduardo Valentin <edubezval@...il.com>, Paul Turner <pjt@...gle.com> Subject: Re: [PATCH 3/4] sched: introduce synchronized idle injection On Wed, Nov 18, 2015 at 12:27:04PM +0000, Morten Rasmussen wrote: > On Wed, Nov 18, 2015 at 11:35:41AM +0100, Peter Zijlstra wrote: > > On Wed, Nov 18, 2015 at 09:36:22AM +0100, Ingo Molnar wrote: > > > What will such throttling do to latencies, as observed by user-space tasks? What's > > > the typical expected frequency of the throttling frequency that you are targeting? > > > > The default has 5ms (iirc) of forced idle, so depending on what you do, > > noticeable to outright painful. > > IIUC, it is 5 ticks, not ms. The code uses hrtimers (badly), this means there _should_ not be a tick dependency. > Which raises the question, doesn't that mean that we get disturbed four > times on each cpu during the forced idle period? So idle injection only > makes sense if the platform has package states with a target residency > less than a jiffy. Or, do we enter NOHZ idle? I haven't looked closely > enough to figure out yet. The idea is to hit NOHZ. -- 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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