[coreboot] CPU Turbo [KGPE-D16]

Timothy Pearson tpearson at raptorengineering.com
Mon Dec 19 19:03:52 CET 2016

Hash: SHA1

On 12/16/2016 07:13 PM, Taiidan at gmx.com wrote:
> y'all helpful as always >:D
> On 12/12/2016 03:00 PM, Timothy Pearson wrote:
> On 12/11/2016 07:52 PM, Taiidan at gmx.com wrote:
>>>> Thanks! helpful as always >:D
>>>> Yes c states and cc6 states are enabled, 1 or 2 cores can get up to
>>>> around 100mhz or so less than turbo 2 however I cannot get the whole
>>>> advertised 8 or even 4 (i get max around 2.5ghz as reported by "cpupower
>>>> monitor" ), my temp is 35C with full load cpu usage and my fans nearly
>>>> off (tower cooler) so I don't think that could be the issue.
> Interesting.  Are these the results of the turbostat program?  What does
> powertop show in the idle stats?
>> Powertop, around 96-98% or so.
>> Turbostat doesn't show turbo frequencies for some reason under tsc_mhz, 
>> and average cpu freq is lower than wcpupower monitor reports.
>> With a single 100% cpu thread I can get to 3ghz (still a little short),
>> however with every thread I add the clock speed goes slightly down.
>> Weird stuff.

I strongly suspect Linux is scheduling threads on the other cores,
causing the black box inside the CPU to momentarily take the highly
loaded CPU(s) out of maximum boost for brief intervals.  turbostat and
friends work by measuring the TSC over a period of time to detect
boosted operation, and being "a little short" of maximum boost is
consistent with this theory.

>> Is there a way to view and force c-states? I tried using
>> turionpowercontrol but it didn't work, the cpu simply clocked up again
>> and it only has a max cstate and not a min cstate option.
>> I am curious is there a way to disable the second half of the 16 core
>> CPU optys in coreboot?

No, you cannot force C-states with a stock kernel.  Coreboot itself has
no control over this; the Linux kernel controls all power saving states
across all cores once started.  One thing you can try is to move all of
your processes (including system processes) onto one group of cores with
cgroup functionality; Linux should then idle the unused cores via the C3
(subsequently hardware-transitioned to CC6) power saving state.

- -- 
Timothy Pearson
Raptor Engineering
+1 (415) 727-8645 (direct line)
+1 (512) 690-0200 (switchboard)
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