linux-kernel - Re: Performance regression in v3.14

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Message-ID: <77867612.qQW44bBzL9@vostro.rjw.lan>
Date:	Fri, 30 May 2014 14:29:47 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Johan Hovold <jhovold@...il.com>,
	Dirk Brandewie <dirk.brandewie@...il.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	dirk.j.brandewie@...el.com,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Doug Smythies <dsmythies@...us.net>,
	Yuyang Du <yuyang.du@...el.com>,
	Stratos Karafotis <stratosk@...aphore.gr>
Subject: Re: Performance regression in v3.14

On Thursday, May 29, 2014 07:27:34 PM Greg Kroah-Hartman wrote:
> On Wed, May 28, 2014 at 09:59:45AM +0200, Johan Hovold wrote:
> > [ +CC: Greg, Doug, Stratos, Yuyang ]
> > 
> > On Wed, May 21, 2014 at 11:00:51AM +0200, Johan Hovold wrote:
> > > On Wed, May 07, 2014 at 07:10:49AM -0700, Dirk Brandewie wrote:
> > > > On 05/06/2014 10:40 PM, Viresh Kumar wrote:
> > > > > Cc'ing Dirk who is taking care of intel-pstate driver.
> > > > >
> > > > 
> > > > Thanks Viresh I had seen this thread.
> > > > 
> > > > I am looking into it
> > > 
> > > Any updates on this, Dirk? 3.14 is still basically unusable with the
> > > intel_pstate driver.
> > > 
> > > Any fixes or workarounds posted elsewhere that I can apply in the
> > > meantime?
> > 
> > Another week and still no reply, Dirk?
> > 
> > I tried applying your (rejected) patch "intel_pstate: Remove C0
> > tracking" posted here:
> > 
> > 	https://lkml.org/lkml/2014/5/8/574
> > 
> > to v3.14.4 and it fixes the problem as expected.
> > 
> > So we have a commit fcb6a15c2e7e ("intel_pstate: Take core C0 time into
> > account for core busy calculation") that went into v3.14-rc2 (and was
> > even marked for *stable*) that first broke Greg KH's system:
> > 
> > 	https://lkml.org/lkml/2014/2/19/626
> > 
> > That was apparently fixed by e66c17683746 ("intel_pstate: Change
> > busy calculation to use fixed point math."), but still left v3.14
> > basically unusable for lower-intensity workloads such as my
> > bash-completion example and other reported regressions:
> > 
> > 	https://bugzilla.kernel.org/show_bug.cgi?id=75121
> > 
> > Sure there may be issues with v3.13 not hitting the lowest frequencies
> > but at least the system was *usable*.
> > 
> > In my opinion there's really no other option than to restore the 3.13
> > behaviour by effectively reverting fcb6a15c2e7e ("intel_pstate: Take
> > core C0 time into account for core busy calculation") until you have
> > figured out a way to take C0 into account without breaking things too
> > badly.
> 
> Dirk has posted some patches, do they fix the problem for you?

I'm queuing up this series for 3.16, BTW.

Rafael

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