[Bug 77771] Intel P-State: Constantly changing CPU frequencies on idle system.

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=77771

--- Comment #7 from Yuyang Du <yuyang.du@intel.com> ---
(In reply to Michael Long from comment #5)
> Thanks for the hint about the turbostat utility. Without starting a desktop
> environment I got similar stats, all frequencies are very close around the
> lowest state. Logged into KDE showed different results. Eventually I found
> the cause of those high clocks: 
> 
> A superkaramba desktop-widget. This widget basically does a grep on
> /proc/cpuinfo and checks the load internally each second. Disabling this
> widget gets the clock down. The same behavior can be reproduced just by
> running "for i in {1..99}; do grep MHz /proc/cpuinfo; sleep 1; done".
> 
> Admittedley this might be a typical layer8-problem, however why is a simple
> grep every second pounding the CPU so hard that it remains in higher clocks,
> even in turbo mode? Especially when it didn't before the patch or just using
> plain old acpi-cpufreq. If this is still just expected behavior sorry for
> the unnecessary noise.

Expected, but should not happen. So clearly something is wrong...

Yuyang

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