linux-kernel - Re: [PATCH] cpufreq: governor: Be friendly towards latency-sensitive bursty workloads

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Message-ID: <2902116.OdbNv5KQzQ@vostro.rjw.lan>
Date:	Tue, 27 May 2014 01:27:54 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	viresh.kumar@...aro.org, svaidy@...ux.vnet.ibm.com,
	ego@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq: governor: Be friendly towards latency-sensitive bursty workloads

Hi Srivatsa,

On Tuesday, May 27, 2014 02:23:38 AM Srivatsa S. Bhat wrote:
> Cpufreq governors like the ondemand governor calculate the load on the CPU
> periodically by employing deferrable timers. A deferrable timer won't fire
> if the CPU is completely idle (and there are no other timers to be run), in
> order to avoid unnecessary wakeups and thus save CPU power.
> 
> However, the load calculation logic is agnostic to all this, and this can
> lead to the problem described below.

This is subtle enough that I need some more time to chew on it, but since the
merge window is coming, I'm not sure when that's going to happen honestly.

Rafael

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