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Date: Thu, 2 Jan 2014 12:38:08 -0500 (EST) From: Mikulas Patocka <mpatocka@...hat.com> To: Viresh Kumar <viresh.kumar@...aro.org> cc: "Rafael J. Wysocki" <rjw@...ysocki.net>, "cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 1/3] powernow-k6: disable cache when changing frequency On Tue, 17 Dec 2013, Viresh Kumar wrote: > On 12 December 2013 06:08, Mikulas Patocka <mpatocka@...hat.com> wrote: > > During frequency transition the processor is in "EPM Stop Grant" state. > > The documentation says that the processor doesn't respond to inquiry > > requests in this state. Consequently, coherency of processor caches and > > bus master devices is not maintained, causing the system instability. > > > > This patch flushes the cache during frequency transition. It fixes the > > instability. > > I don't have much idea of these systems but wouldn't this affect performance > badly? Flushing the cache and changing frequency takes approximatelly 500us. The patch increases policy->cpuinfo.transition_latency to that value. I suppose that the governors should be smart enough to not do frequency transitions so often so that majority of time is spent doing the transition. Mikulas -- 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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