linux-kernel - Re: [RFC PATCH] Increase in idle power with schedutil

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Message-ID: <20160519114029.GW3193@twins.programming.kicks-ass.net>
Date:	Thu, 19 May 2016 13:40:29 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>,
	shreyas@...ux.vnet.ibm.com, akshay.adiga@...ux.vnet.ibm.com,
	linuxppc-dev@...abs.org, Steve Muckle <steve.muckle@...aro.org>
Subject: Re: [RFC PATCH] Increase in idle power with schedutil

On Wed, May 18, 2016 at 11:11:51PM +0200, Rafael J. Wysocki wrote:
> On Wed, May 18, 2016 at 2:53 PM, Shilpasri G Bhat
> <shilpa.bhat@...ux.vnet.ibm.com> wrote:
> > This patch adds driver callback for fast_switch and below observations
> > on schedutil governor are done with this patch.
> >
> > In POWER8 there is a regression observed with schedutil compared to
> > ondemand. With schedutil the frequency is not ramping down and is
> > mostly stuck at max frequency during idle . This is because of the
> > watchdog timer, an RT task which is fired every 4 seconds which
> > results in requesting max frequency.
> 
> Well, yes, that would be problematic.
> 

Right; we need to come up with something for RT tasks; but what happens
if you disable the watchdog? This should be entirely doable and might
give a better comparison.