Dear Rafael,
On 12/13/18 11:39, Rafael J. Wysocki wrote:
> On Thu, Dec 13, 2018 at 10:54 AM Paul Menzel <pmen...@molgen.mpg.de> wrote:
>> On 12/13/18 00:06, Doug Smythies wrote:
>>> On 2018.12.12 13:40 Paul Menzel wrote:
>>>
>>>> Using *powersave* as P-state selection algorithm, on an idle system
>>>
>>> Define "idle system".
>>> If your computer is running a GUI, or is even a server without a GUI
>>> but with many services running, then "idle" really isn't.
>>> Below is from my test server, with many services disabled, so
>>> "idle" really is quite "idle"
>>>
>>> doug@s15:~/temp$ sudo turbostat --Summary --quiet --show
>>> Busy%,Bzy_MHz,PkgTmp,PkgWatt --interval 15
>>> Busy% Bzy_MHz PkgTmp PkgWatt
>>> 0.01 1608 27 3.71
>>> 0.01 1619 27 3.71
>>> 0.01 1600 28 3.71
>>> 0.01 1600 28 3.70
>>>
>>> Note that p state 16 (1600 MHz) is the minimum for my older i7-2600k
>>> processor.
>>
>> The thing is, on an Intel Kaby Lake laptop with Ubuntu 18.10 and GNOME
>> running, it goes down to the lowest listed frequency.
Checking the numbers again, I was mistaken. The lowest possible frequency
of the Intel Kaby Lake i7-7500U in that laptop is 400 MHz, and it is
going down to 600 MHz. Busy% from turbostat is 0.3 to 0.4.
> Kaby Lake has hardware-managed P-states (HWP) which is a different mechanism.
Isn’t HWP also available for the 6th generation?
$ dmesg | grep intel_pstate
[ 2.092456] intel_pstate: Intel P-state driver initializing
[ 2.094820] intel_pstate: HWP enabled
>>>> Shouldn’t it go down until 800 MHz?
>>>
>>> We would need some actual busy information, turbostat is the
>>> recommended tool, to know for sure.
>>
>> Here you go.
>>
>> ```
>> tools/power/x86/turbostat> sudo ./turbostat --Summary --quiet --show
>> Busy%,Bzy_MHz,PkgTmp,PkgWatt --interval 15
>> Busy% Bzy_MHz PkgTmp PkgWatt
>> 3.59 1167 31 1.68
>> 3.21 903 31 1.34
>> 3.21 906 31 1.34
>> 3.27 901 31 1.35
>> 8.23 2715 30 2.32 ← stopping GDM (systemctl stop gdm)
>> 2.95 915 30 1.18
>> 2.91 906 30 1.18
>> 2.92 903 30 1.17
>> 2.90 900 29 1.17
>> 2.89 903 29 1.18
>> 2.91 903 30 1.18
>> 2.89 903 29 1.18
>> 2.89 900 29 1.18
>> 2.90 903 30 1.18
>> 2.90 903 29 1.17
>> 2.90 903 29 1.17
>> 2.90 900 29 1.16
>> 2.90 903 29 1.14
>> 2.90 903 28 1.11
>> 2.90 903 29 1.10
>> 2.91 900 29 1.16
>> 2.91 903 29 1.14
>> 2.90 903 29 1.12
>> 2.90 903 29 1.16
>> 2.90 900 28 1.17
>> 2.92 903 29 1.16
>> 2.90 903 29 1.16
>> 2.90 903 29 1.16
>> ```
>>
>> 800 MHz should be enough to keep GDM running, shouldn’t it?
>
> Well, depending.
>
>> Otherwise only SSH was running.
>
> There obviously is something that causes it to stay at 900 MHz.
It’s not obvious to me, but you have more experience. It’d expect
to at least one core(?) to go down to 800 MHz and not all to stay
at 900 MHz.
> Please check max_perf_pct, min_perf_pct and num_pstates under
> /sys/devices/system/cpu/intel_pstate/ .
/sys/devices/system/cpu/intel_pstate> cat max_perf_pct min_perf_pct
num_pstates
100
20
33
> Also cpuinfo_max_freq, cpuinfo_min_freq, scaling_max_freq,
> scaling_min_freq under /sys/devices/system/cpu/cpufreq/policy0/ .
/sys/devices/system/cpu/cpufreq/policy0> cat cpuinfo_{min,max}_freq
scaling_{min,max}_freq
800000
4000000
800000
4000000
> However, please note that Busy% of 3 isn't particularly low.
Indeed. On the laptop it is around 0.3 to 0.4 even with GNOME
running.
So, to check if everything is working, I boot into initramfs
and check the numbers there?
Kind regards,
Paul
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