linux-kernel - Re: [intel-pstate driver regression] processor frequency very high even if in idle

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Message-ID: <1459536104.13525.148.camel@linux.intel.com>
Date:	Fri, 01 Apr 2016 11:41:44 -0700
From:	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:	Doug Smythies <dsmythies@...us.net>,
	'Jörg Otte' <jrg.otte@...il.com>,
	"'Rafael J. Wysocki'" <rjw@...ysocki.net>
Cc:	"'Rafael J. Wysocki'" <rafael@...nel.org>,
	'Linux Kernel Mailing List' <linux-kernel@...r.kernel.org>,
	'Linux PM list' <linux-pm@...r.kernel.org>
Subject: Re: [intel-pstate driver regression] processor frequency very high
 even if in idle

On Fri, 2016-04-01 at 11:31 -0700, Doug Smythies wrote:
> On 2106.034.01 10:45 Srinivas Pandruvada wrote:
> > 
> > On Fri, 2016-04-01 at 16:06 +0200, Jörg Otte wrote:
> > > 
> > > > 
> > > > > 
> > > > > > 
> > > > > > > 
> > > > > > > 
> > > Done. Attached the tracer.
> > > For me it looks like the previous one of the failing case.
> > The traces show that idle task is constantly running without sleep.
> No,
I mean atleast on once CPU. I am not saying they are looping, but the
wakeup time is less than 10ms, so the driver will not scale the load
for idle time.

>  they (at least the first one, I didn't look at the next one yet)
> show that CPUs 2 and 3 are spending around 99% of their time not in
> state
> C0. That the sample rate is ending up at ~10 Milliseconds, indicates
> some
> high frequency (>= 100Hz) events on those CPUs. Those events,
> apparently,
> take very little CPU time to complete, hence a load of about 1% on
> average.
> 
> By the way, I can recreate the high sample rate with virtually no
> load
> on my system easy, but so far have been unable to get the high CPU
> frequencies observed by Jörg. I can get my system to about a target
> pstate of
> 20 where it should have remained at 16, but that is about it.
> 
> > 
> > The driver is processing samples for idle task for every 10ms and
> > aperf/mperf are showing that we are always in turbo mode for idle
> > task.
> That column pretty much always says "idle" (or swapper for my way of
> doing
> things). I have not found it to very useful as an indicator, and
> considerably
> more so since the utilization changes.
> 
> > 
> > 
> > Need to find out why idle task is not sleeping.
> I contend that is it.
> I don't have enough reverted data, but so far this seems very much
> like
> that bug report I referenced earlier.
> 
> ... Doug
> 
> 
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