linux-kernel - Re: intel_pstate: Lowest frequency not reached with Intel i7-6700

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Message-ID: <a4321c48-e9df-1a2a-cfbd-bac07a9c65d8@molgen.mpg.de>
Date:   Thu, 13 Dec 2018 10:54:05 +0100
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Doug Smythies <dsmythies@...us.net>
Cc:     linux-pm@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>
Subject: Re: intel_pstate: Lowest frequency not reached with Intel i7-6700

Dear Doug,


Thank you for your reply.

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.

>> 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?
Otherwise only SSH was running.


Kind regards,

Paul


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