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