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Wrong cores frequencies values in /proc/cpuinfo

Bug 197153 [email protected] 1 participant 11 messages Oct 7, 2017 – Oct 16, 2017 1 message not in the archive

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https://bugzilla.kernel.org/show_bug.cgi?id=197153

Doug Smythies ([email protected]) changed:

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--- Comment #1 from Doug Smythies ([email protected]) --- this is a duplicate of bug #197009.
the change was intentional.

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Artem S. Tashkinov ([email protected]) changed:

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--- Comment #2 from Artem S. Tashkinov ([email protected]) --- This breaks a lot of user space applications which report frequencies.

CC'ing Linus Torvalds.

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Artem S. Tashkinov ([email protected]) changed:

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--- Comment #4 from Artem S. Tashkinov ([email protected]) --- (In reply to Doug Smythies from comment #3)

Quoted 2 lines

Back on bug #197009, I couldn't find the related e-mail thread. Now I did:
https://marc.info/?t=149766883400002&r=1&w=2

Thanks!

Quoted 11 lines

Users who have been consulting /proc/cpuinfo to track changing CPU frequency will be dissapointed that it no longer wiggles -- perhaps being unaware of the limitations of the information they have been consuming.

Yes, they can change their scripts to look in sysfs cpufreq/scaling_cur_frequency. Here they will find the same data of dubious quality here removed from /proc/cpuinfo. The value in sysfs will be addressed in a subsequent patch to address issues 1-3, above.

Quoted 5 lines

Issue 4 will remain -- users that really care about accurate frequency information should not be using either proc or sysfs kernel interfaces.
They should be using using turbostat(8), or a similar purpose-built analysis tool.

That sounds like a dozen of Linux utilities need to be rewritten to either include the turbostat source (how do you even see that? what about updates to this code?) or ... Len Brown has some other ideas in mind? Does turbostat work without insmod()'ing the msr module first? Most distros don't autopreload it.

You break the user space interfaces and don't offer any realistic alternatives at all. I for one refuse to run turbostat in console just to know what frequencies my CPU cores are running at.

This is not how it should work.

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https://bugzilla.kernel.org/show_bug.cgi?id=197153

--- Comment #5 from Artem S. Tashkinov ([email protected]) --- While we're at it I don't understand why I see four different values at

/sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq

My CPU has just two physical cores (the two others are HT). I'm OK with Value0 Value0 and Value1 Value1 but not with four different values. I understand that frequencies are dynamic but not that dynamic so that the cat utility which completes in under 0.001 seconds could see four quite different values.

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--- Comment #6 from Artem S. Tashkinov ([email protected]) --- The /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq interface is also broken in 4.13.

This one liner:

cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq | awk '{if (max<$0) max=$0}END{printf "%.2fGHz",max/1000000}'

prints values from 0.50GHz to 2.55GHz even though my laptop is more or less completely idle (no running applications aside from XFCE itself).

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--- Comment #7 from Doug Smythies ([email protected]) --- @Artem: Please be considerate that, since this bug is unassigned, emails are going to the entire linux-pm e-mail list.

Quoted 2 lines

The /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq interface is also broken in 4.13.

It is not broken, and the numbers you are getting are most probably correct. If you are running a desktop computer with a GUI, then this statement:

"my laptop is more or less completely idle"

simply is not true. You would have to disable the GUI and a bunch of other services to get a more idle system (which would still not be completely idle).

If I use my test Ubuntu 16.04.3 server (no GUI) and disable several services, i.e.:

$ cat set_cpu_turn_off_services
#! /bin/bash
# Turn off some services to try to get "idle" to be more "idle"
sudo systemctl stop mysql.service
sudo systemctl stop apache2.service
sudo systemctl stop nmbd.service
sudo systemctl stop smbd.service
sudo systemctl stop cron.service
sudo systemctl stop winbind.service
sudo systemctl stop apt-daily.timer

then for your command I usually get 1.61 GHz, which is the minimum for my processor.

In order to not influence the system I was testing, I ran your command at a very slow rate of once every 2 seconds for 6112 samples. 5970 (97.68%) of them reported the minimum frequency for my 8 CPU processor.

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Zhang Rui ([email protected]) changed:

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--- Comment #8 from Zhang Rui ([email protected]) --- *** Bug 197017 has been marked as a duplicate of this bug. ***

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