linux-kernel - Re: [RFC][PATCH 5/7] cpufreq / sched: UUF

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Date:	Tue, 2 Aug 2016 03:37:02 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Steve Muckle <steve.muckle@...aro.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Juri Lelli <juri.lelli@....com>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC][PATCH 5/7] cpufreq / sched: UUF_IO flag to indicate iowait condition

On Tue, Aug 2, 2016 at 3:22 AM, Steve Muckle <steve.muckle@...aro.org> wrote:
> On Mon, Aug 01, 2016 at 01:37:23AM +0200, Rafael J. Wysocki wrote:
> ...
>> For this purpose, define a new cpufreq_update_util() flag
>> UUF_IO and modify enqueue_task_fair() to pass that flag to
>> cpufreq_update_util() in the in_iowait case.  That generally
>> requires cpufreq_update_util() to be called directly from there,
>> because update_load_avg() is not likely to be invoked in that
>> case.
>
> I didn't follow why the cpufreq hook won't likely be called if
> in_iowait is set? AFAICS update_load_avg() gets called in the second loop
> and calls update_cfs_rq_load_avg (triggers the hook).

In practice it turns out that in the majority of cases when in_iowait
is set the second loop will not run.

Thanks,
Rafael