linux-kernel - Re: [PATCH 1/3] powernow-k6: disable cache when changing frequency

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Message-ID: <alpine.LRH.2.02.1401061514450.25034@file01.intranet.prod.int.rdu2.redhat.com>
Date:	Mon, 6 Jan 2014 15:17:13 -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 Fri, 3 Jan 2014, Viresh Kumar wrote:

> On 2 January 2014 23:08, Mikulas Patocka <mpatocka@...hat.com> wrote:
> > Flushing the cache and changing frequency takes approximatelly 500us. The
> > patch increases policy->cpuinfo.transition_latency to that value.
> 
> Its not about how fast caches get cleaned but how much time would
> be wasted to get them filled again as same data could be required again
> which is just flushed out. That would impact performance more than
> flushing caches.

I didn't see any performance degradation when I tried changing the 
frequency manually with or without the cache flush patch - the overhead of 
running cpufreq (8ms) is far worse than the frequency transition itself.

Mikulas
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