linux-kernel - Re: Regression in 4.8 - CPU speed set very low

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Date:   Mon, 26 Sep 2016 18:30:46 -0700
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     Larry Finger <Larry.Finger@...inger.net>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: Regression in 4.8 - CPU speed set very low

On Mon, 2016-09-26 at 19:48 -0500, Larry Finger wrote:
> On 09/26/2016 07:21 PM, Rafael J. Wysocki wrote:
> > 
> > On Tue, Sep 27, 2016 at 1:53 AM, Larry Finger <Larry.Finger@...inge
> > r.net> wrote:
> > > 
> > > On 09/26/2016 05:16 PM, Rafael J. Wysocki wrote:
> > > > 
> > > > 
> > > > On Tue, Sep 27, 2016 at 12:09 AM, Larry Finger
> > > <Larry.Finger@...inger.net> wrote:
> > > > 
> > > > 
> > > > 
> > > > Maybe it's better to try diagnose the problem instead of
> > > > spending more
> > > > time on bisection.
> > > 
> > > In my original post, I asked for such help, but nothing until
> > > today. I had
> > > no idea what to check, but now I have a better idea.
> > > 
> > > > 
> > > > I'd like to know whether or not 4.7 was definitely good,
> > > > though.
> > > 
> > > I never saw this problem with 4.7, but given the difficulty in
> > > triggering
> > > the problem, my tests may not have been definitive.
> > > > 
> > > > 
> > > > 
> > > > > 
> > > > > If it is one of them, it may be a while before I dare call
> > > > > this one
> > > > > "good".
> > > > > In one respect, that is good as I will be traveling tomorrow
> > > > > and
> > > > > Wednesday.
> > > > 
> > > > What does "cat
> > > > /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver" say?
> > > 
> > > intel_pstate
> > You probably don't need to worry about all of the cpufreq changes
> > in
> > 4.8-rc, then.  Only a few of them affect intel_pstate and I don't
> > see
> > how any of them may lead to the observed symptoms.
> > 
> > First off, if you have a reproducer, please run it on 4.7 and see
> > if
> > you can trigger the issue in there.
> I'm running 4.8-rc7 at the moment hoping to trigger the problem and
> get the data 
> requested by Srinivas. Once I get that, I will try 4.7 again.
> > 
> > 
> > Second, it would be good to have a look at the output from the
> > cpu_frequency and pstate_sample tracepoints around when the issue
> > triggers.  The pstate_sample one would be more interesting.
> > 
> > But for both we need a reproducer anyway.
> I do not have a reliable reproducer. The condition has always
> happened when 
> running a high-compute job such as a 'make -j8' on the kernel, or
> building the 
> RPM for openSUSE's implementation of VirtualBox. The latter is what
> I'm using 
> for most of my testing.
> 
> > 
> > It also would be good to rule out the thermal throttling (as per
> > the
> > Srinivas' comments).
> > 
> > For now, please tell me what's in
> > /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq
> 800000
Your effective freq is lower than 800MHz. One of the possible reason is
thermal throttling.

What distro you are using?


Thanks,
Srinivas