* [RFC] why do sensors break CPU scaling
@ 2019-11-20 20:42 Tom Psyborg
2019-11-21 1:51 ` David Niklas
2020-01-31 22:35 ` Pavel Machek
0 siblings, 2 replies; 5+ messages in thread
From: Tom Psyborg @ 2019-11-20 20:42 UTC (permalink / raw)
To: Linux Kernel Mailing List
Hi
Recently I've needed to set lowest CPU scaling profile, running ubuntu
16.04.06 I used standard approach - echoing powersave to
/sys/devices/system/cpu/cpu*/cpufreq/scaling_governor.
This did not work as the
/sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_cur_freq kept returning
max scaling freq.
During testing of ubuntu 19.10 I've found that the above approach
actually does work, but as long as there are no xsensors (or just
sensors from cli) being run.
cpuinfo_cur_freq in this case was returning variable values +- 1% of
around 1.4GHz.
As soon as I issue sensors command cpuinfo_cur_freq jumps to 3.5GHz
for a fraction of second and returns back to 1.4GHz afterwards. If
running xsensors it keeps bouncing between 1.4 and 3.5GHz all the
time.
Rebooted back to 16.04.6 and was able to set lowest CPU scaling freq
as well, but issuing sensors command here once just breaks CPU scaling
that now remains at about 3.5GHz.
It can be set to lowest scaling freq again without rebooting but it
needs to change scaling_governor for all cores to something else and
then back to powersave.
Why is this happening, shouldn't sensors command just read temp/fan
values without writing to any of the CPU control registers?
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [RFC] why do sensors break CPU scaling
2019-11-20 20:42 [RFC] why do sensors break CPU scaling Tom Psyborg
@ 2019-11-21 1:51 ` David Niklas
2019-11-23 13:44 ` Tom Psyborg
2020-01-31 22:35 ` Pavel Machek
1 sibling, 1 reply; 5+ messages in thread
From: David Niklas @ 2019-11-21 1:51 UTC (permalink / raw)
To: Tom Psyborg; +Cc: Linux Kernel Mailing List
On Wed, 20 Nov 2019 21:42:12 +0100
Tom Psyborg <pozega.tomislav@gmail.com> wrote:
> Hi
>
> Recently I've needed to set lowest CPU scaling profile, running ubuntu
> 16.04.06 I used standard approach - echoing powersave to
> /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor.
> This did not work as the
> /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_cur_freq kept returning
> max scaling freq.
>
> During testing of ubuntu 19.10 I've found that the above approach
> actually does work, but as long as there are no xsensors (or just
> sensors from cli) being run.
> cpuinfo_cur_freq in this case was returning variable values +- 1% of
> around 1.4GHz.
> As soon as I issue sensors command cpuinfo_cur_freq jumps to 3.5GHz
> for a fraction of second and returns back to 1.4GHz afterwards. If
> running xsensors it keeps bouncing between 1.4 and 3.5GHz all the
> time.
>
> Rebooted back to 16.04.6 and was able to set lowest CPU scaling freq
> as well, but issuing sensors command here once just breaks CPU scaling
> that now remains at about 3.5GHz.
> It can be set to lowest scaling freq again without rebooting but it
> needs to change scaling_governor for all cores to something else and
> then back to powersave.
>
> Why is this happening, shouldn't sensors command just read temp/fan
> values without writing to any of the CPU control registers?
I don't know if the maintainers will notice your email, but I did. I
don't guarantee that they'll notice or help you, but this should assist
you in writing a proper question.
You need to include the output of uname -a on both ubuntu boxes. The
output of:
dpkg -l xsensors
dpkg -l lm-sensors
The information on which processor you own and the motherboard and
it's BIOS version just in case.
This is just my understanding and it might be wrong, but the CPU is
probably accessed to do the request to the fan values and so it ramps up
expecting to have to deal with a more intense workload (which is exactly
what Ryzen and several newer Intel processors are supposed to do), and so
you're seeing expected behavior.
I've no idea how you'd change this.
Alternatively, and this is just a theory, you could have some program on
the system changing the behavior of the CPU just after you change it to
what you want it to be. As in, inotify is involved.
You're welcome,
David
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [RFC] why do sensors break CPU scaling
2019-11-21 1:51 ` David Niklas
@ 2019-11-23 13:44 ` Tom Psyborg
0 siblings, 0 replies; 5+ messages in thread
From: Tom Psyborg @ 2019-11-23 13:44 UTC (permalink / raw)
To: David Niklas; +Cc: Linux Kernel Mailing List
On 21/11/2019, David Niklas <Hgntkwis@vfemail.net> wrote:
> On Wed, 20 Nov 2019 21:42:12 +0100
> Tom Psyborg <pozega.tomislav@gmail.com> wrote:
>> Hi
>>
>> Recently I've needed to set lowest CPU scaling profile, running ubuntu
>> 16.04.06 I used standard approach - echoing powersave to
>> /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor.
>> This did not work as the
>> /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_cur_freq kept returning
>> max scaling freq.
>>
>> During testing of ubuntu 19.10 I've found that the above approach
>> actually does work, but as long as there are no xsensors (or just
>> sensors from cli) being run.
>> cpuinfo_cur_freq in this case was returning variable values +- 1% of
>> around 1.4GHz.
>> As soon as I issue sensors command cpuinfo_cur_freq jumps to 3.5GHz
>> for a fraction of second and returns back to 1.4GHz afterwards. If
>> running xsensors it keeps bouncing between 1.4 and 3.5GHz all the
>> time.
>>
>> Rebooted back to 16.04.6 and was able to set lowest CPU scaling freq
>> as well, but issuing sensors command here once just breaks CPU scaling
>> that now remains at about 3.5GHz.
>> It can be set to lowest scaling freq again without rebooting but it
>> needs to change scaling_governor for all cores to something else and
>> then back to powersave.
>>
>> Why is this happening, shouldn't sensors command just read temp/fan
>> values without writing to any of the CPU control registers?
>
> I don't know if the maintainers will notice your email, but I did. I
> don't guarantee that they'll notice or help you, but this should assist
> you in writing a proper question.
> You need to include the output of uname -a on both ubuntu boxes. The
> output of:
> dpkg -l xsensors
> dpkg -l lm-sensors
this is on 16.04.6
whtw46ww4@I5576:~$ uname -a
Linux I5576 4.15.0-51-generic #55~16.04.1-Ubuntu SMP Thu May 16
09:24:37 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
whtw46ww4@I5576:~$ dpkg -l xsensors
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version
Architecture Description
+++-=============================================-===========================-===========================-===============================================================================================
ii xsensors 0.70-3
amd64 hardware health information viewer
whtw46ww4@I5576:~$ dpkg -l lm-sensors
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version
Architecture Description
+++-=============================================-===========================-===========================-===============================================================================================
ii lm-sensors 1:3.4.0-2
amd64 utilities to read
temperature/voltage/fan sensors
>
> The information on which processor you own and the motherboard and
> it's BIOS version just in case.
>
> This is just my understanding and it might be wrong, but the CPU is
> probably accessed to do the request to the fan values and so it ramps up
> expecting to have to deal with a more intense workload (which is exactly
> what Ryzen and several newer Intel processors are supposed to do), and so
> you're seeing expected behavior.
I don't think that is the case here, since I can run any kind of more
demanding app than xsensors is, even compile software with -j 5
(multithread) and CPU clocks don't exceed 1.40GHz. Only on xsensors
launch CPU clocks are reset.
Regards, Tom
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [RFC] why do sensors break CPU scaling
2019-11-20 20:42 [RFC] why do sensors break CPU scaling Tom Psyborg
2019-11-21 1:51 ` David Niklas
@ 2020-01-31 22:35 ` Pavel Machek
2020-02-01 0:16 ` Tom Psyborg
1 sibling, 1 reply; 5+ messages in thread
From: Pavel Machek @ 2020-01-31 22:35 UTC (permalink / raw)
To: Tom Psyborg; +Cc: Linux Kernel Mailing List
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On Wed 2019-11-20 21:42:12, Tom Psyborg wrote:
> Hi
>
> Recently I've needed to set lowest CPU scaling profile, running ubuntu
> 16.04.06 I used standard approach - echoing powersave to
> /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor.
> This did not work as the
> /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_cur_freq kept returning
> max scaling freq.
Noone noticed, right?
If you still believe that's problem, you may want to look at
MAINTAINERS file, and put sensors maintainers in the Cc list.
Best regards,
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [RFC] why do sensors break CPU scaling
2020-01-31 22:35 ` Pavel Machek
@ 2020-02-01 0:16 ` Tom Psyborg
0 siblings, 0 replies; 5+ messages in thread
From: Tom Psyborg @ 2020-02-01 0:16 UTC (permalink / raw)
To: Pavel Machek; +Cc: Linux Kernel Mailing List, lm-sensors
On 31/01/2020, Pavel Machek <pavel@ucw.cz> wrote:
> On Wed 2019-11-20 21:42:12, Tom Psyborg wrote:
>> Hi
>>
>> Recently I've needed to set lowest CPU scaling profile, running ubuntu
>> 16.04.06 I used standard approach - echoing powersave to
>> /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor.
>> This did not work as the
>> /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_cur_freq kept returning
>> max scaling freq.
>
> Noone noticed, right?
>
> If you still believe that's problem, you may want to look at
> MAINTAINERS file, and put sensors maintainers in the Cc list.
>
> Best regards,
> Pavel
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures)
> http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
>
it is definitely a problem. i've installed radeon-profile and can
monitor both CPU and GPU temps from there without CPU scaling
breakage. CCing related list
^ permalink raw reply [flat|nested] 5+ messages in thread
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2019-11-20 20:42 [RFC] why do sensors break CPU scaling Tom Psyborg
2019-11-21 1:51 ` David Niklas
2019-11-23 13:44 ` Tom Psyborg
2020-01-31 22:35 ` Pavel Machek
2020-02-01 0:16 ` Tom Psyborg
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