linux-kernel - Re: [PATCH 1/7] sched: Introduce scale-invariant load tracking

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Date:	Fri, 10 Oct 2014 11:16:21 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Dietmar Eggemann <dietmar.eggemann@....com>
Cc:	Yuyang Du <yuyang.du@...el.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"pjt@...gle.com" <pjt@...gle.com>,
	"bsegall@...gle.com" <bsegall@...gle.com>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"nicolas.pitre@...aro.org" <nicolas.pitre@...aro.org>,
	"mturquette@...aro.org" <mturquette@...aro.org>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/7] sched: Introduce scale-invariant load tracking

On Wed, Oct 08, 2014 at 01:54:58PM +0100, Dietmar Eggemann wrote:

> > But this should be very hard. Intel Architecture has limitation to capture all
> > the freq changes in software and also the intel_pstate should have no
> > notification.
> 
> We encountered this missing notification for current frequency with
> Intel systems (e.g. i5-3320M) using the intel_pstate driver while
> testing this patch-set. The arch_scale_set_curr_freq call in
> __cpufreq_notify_transition [[PATCH 2/7] cpufreq: Architecture specific
> callback for frequency changes] will not work on such a system.
> 
> In our internal testing, we placed arch_scale_set_curr_freq(cpu->cpu,
> sample->freq) into intel_pstate_timer_func [intel_pstate.c] to get the
> current frequency for a cpu.
> 
> The arch_scale_set_max_freq call in cpufreq_set_policy
> [drivers/cpufreq/cpufreq.c] still works although the driver exposes the
> max turbo pstate and not the max pstate. That's an additional problem
> because we don't want to use turbo states for frequency scaling.

Right, so when we pull the policy part into the scheduler, intel_pstate
will revert to just another driver without such logic and things should
just work.

But yes, currently it also implements policy, that needs to go away.
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