linux-kernel - RE: [RFC/RFT][PATCH] cpufreq: intel_pstate: Accept passive mode with HWP enabled

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Message-ID: <000201d63776$2d56f330$8804d990$@net>
Date:   Sun, 31 May 2020 11:06:13 -0700
From:   "Doug Smythies" <dsmythies@...us.net>
To:     "'Srinivas Pandruvada'" <srinivas.pandruvada@...ux.intel.com>,
        "'Rafael J. Wysocki'" <rjw@...ysocki.net>
Cc:     "'LKML'" <linux-kernel@...r.kernel.org>,
        "'Len Brown'" <len.brown@...el.com>,
        "'Peter Zijlstra'" <peterz@...radead.org>,
        "'Giovanni Gherdovich'" <ggherdovich@...e.cz>,
        "'Francisco Jerez'" <francisco.jerez.plata@...el.com>,
        "'Linux PM'" <linux-pm@...r.kernel.org>
Subject: RE: [RFC/RFT][PATCH] cpufreq: intel_pstate: Accept passive mode with HWP enabled

Hi Srinivas,

Thanks you for your quick reply.

On 2020.05.31 09:54 Srinivas Pandruvada wrote
> On Sun, 2020-05-31 at 09:39 -0700, Doug Smythies wrote:

>> Event begins at 17.456 seconds elapsed time.
>> Previous event was about 107 milliseconds ago.
>>
>> Old min ; new min ; freq GHz; load % ; duration mS
>> 27      ; 28      ; 4.60    ; 68.17  ; 10.226
>> 28      ; 26      ; 4.53    ; 57.47  ; 10.005
> 
> Seems you hit power/thermal limit

No.

I am nowhere near any power limit at all.
I have meticulously configured and tested the thermal management of this computer.
I never ever hit a thermal limit and have TDP set such that the processor
temperature never exceeds about 75 degrees centigrade.

There should never be throttling involved in these experiments.
I can achieve throttling when compiling the kernel and with
torture test mode on the mprime test (other CPU stressors,
including my own, are not as good at generating heat as
mprime).

This system can run indefinitely at 99.9 watts processor package power.
Example (turbostat, steady state, CPU freq throttled to 4.04 GHz):

doug@s18:~$ sudo ~/turbostat --Summary --quiet --show Busy%,Bzy_MHz,PkgTmp,PkgWatt,GFXWatt,IRQ --interval 12
Busy%   Bzy_MHz IRQ     PkgTmp  PkgWatt GFXWatt
100.21  4045    72231   66      99.93   0.00
100.21  4043    72239   65      99.92   0.00

> 
> Is this some Lenovo system?

No. The web page version of my original e-mail has
a link to the test computer hardware profile.

The motherboard is ASUS PRIME Z390-P.

> 
> If you disable HWP you don't see that?

Correct.

> 
> What is the value of
> cat /sys/bus/pci/devices/0000\:00\:04.0/tcc_offset_degree_celsius

? "No such file or directory"

> cat /sys/class/powercap/intel-rapl-mmio/intel-rapl-
> mmio:0/constraint_0_power_limit_uw

? "No such file or directory"

> You may want to run
> Try running dptfxtract once.

No, I am not going to.

I am not running thermald. Eventually I will, as a backup
in case of cooling failure, so as not to hit the processor limit
shutdown. I just haven't done it yet.

> 
> Then try to get again
> 
> cat /sys/bus/pci/devices/0000\:00\:04.0/tcc_offset_degree_celsius
> cat /sys/class/powercap/intel-rapl-mmio/intel-rapl-
> mmio:0/constraint_0_power_limit_uw
> 
> 
> Thanks,
> Srinivas