Wrong max Turbo frequency

English Hardware
1

Hi all,

I would like to ask for some help on trying workarounds on the problem below:

I have an Intel Core i7-7500U processor, with base frequency 2.7GHz and max turbo frequency 3.5GHz.
However, cpuinfo_max_freq and scaling_max_freq from /sys/devices/system/cpu/cpu*/ are reporting wrong maximum frequency of 2700000.
Corroborating or not with this issue, on heavy CPU activity Turbo Boost does not achieve Turbo max frequency ~3.5GHz (above 2.7GHz), which is asserted from frequency-info and i7z.
I have tested with a stress test like <stress-ng --cpu 4 --io 2 --vm 1 --vm-bytes 1G --timeout 60s --metrics-brief> and running several firefox tabs with heavy cpu load at the same time.

So, I have being thinking on trying a possible workaround like writing the right maximum frequency into cpuinfo_max_freq. Is it ok to do it?

I have noticed that cpuinfo_max_freq has read-only permission, so that a .conf file in /etc/tmpfiles.d should not have an effect without changing this permission. Is it ok to do it?

On the other hand, scaling_max_freq is editable. But changing it does not make any effect, which I believe may be related to the limit in cpuinfo_max_freq. Additionally,

sudo cpupower frequency-set --max 3500000

runs, but does not any effect either.

Do you have any other suggestion?

Thanks in advance :slight_smile:

– Reproducibility:
It is always reproducible whether tlp is enabled or disabled on AC power.

It happens on Leap 15 with kernel 4.12, 4.14 LTS and latest stable 4.16.

– Bug reported:
https://bugzilla.opensuse.org/show_bug.cgi?id=1097322

– Possibly related issue:
https://forums.opensuse.org/showthread.php/517131-CPU-can-t-reach-its-maximum-frequency?highlight=cpuinfo_max_freq

2

With my i5-8250U cpu I see the max. turbo frequency of 3.5 GHz, but depending on the load not long. The base frequency is 1.6 GHz and the average frequency under multi core load is 2.4 GHz.
The more cpu cores, I stress, the faster the cpu reduces the frequency.
Could you try again with settings that stress only one core ? ("–cpu 1")

Hendrik

3

On Thu 14 Jun 2018 07:26:03 PM CDT, hendwolt wrote:

With my i5-8250U cpu I see the max. turbo frequency of 3.5 GHz, but
depending on the load not long. The base frequency is 1.6 GHz and the
average frequency under multi core load is 2.4 GHz.
The more cpu cores, I stress, the faster the cpu reduces the frequency.
Could you try again with settings that stress only one core ? (“–cpu
1”)

Hendrik

Hi
Also check the output (as root user) from the following command;


cpupower frequency-info

I have an i5-3210M system, max at 1 core is 3.5GHz, any more it’s 2.9GHz

The other option (which I do with my AMD systems) is monitor the
cpupower mperf option as this shows it boosting (turbo) whereas user
space tools don’t show this, just max frequency not boost states.

–
Cheers Malcolm °¿° SUSE Knowledge Partner (Linux Counter #276890)
SLES 15 | GNOME Shell 3.26.2 | 4.12.14-23-default
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4

Hi,

Thank very much.

What has help here is Kernel 4.14 LTS, which seems to solved the maximum frequency issue.

However, this decrease in frequency under heavy load (as far as I could conclude from vast searches on the web) is a “feature” of the Turbo Boost itself to protect the hardware.