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I installed recently Kubuntu 11.10 32 bits (had graphics driver issues, wanted to try on 32 bits version) on my new Alienware M17x, with a Core i7-2670QM CPU. Cores are supposed to be clocked at 2.2 GHz, however the output of

$ cat /proc/cpuinfo | grep -i "hz"

gives me:

model name      : Intel(R) Core(TM) i7-2670QM CPU @ 2.20GHz
cpu MHz         : 800.000
model name      : Intel(R) Core(TM) i7-2670QM CPU @ 2.20GHz
cpu MHz         : 800.000
model name      : Intel(R) Core(TM) i7-2670QM CPU @ 2.20GHz
cpu MHz         : 800.000
model name      : Intel(R) Core(TM) i7-2670QM CPU @ 2.20GHz
cpu MHz         : 800.000
model name      : Intel(R) Core(TM) i7-2670QM CPU @ 2.20GHz
cpu MHz         : 800.000
model name      : Intel(R) Core(TM) i7-2670QM CPU @ 2.20GHz
cpu MHz         : 800.000
model name      : Intel(R) Core(TM) i7-2670QM CPU @ 2.20GHz
cpu MHz         : 800.000
model name      : Intel(R) Core(TM) i7-2670QM CPU @ 2.20GHz
cpu MHz         : 800.000

If useful, the AC adapter is plugged in (yet the ouput is the same when the computer is powered only by the battery) and I have Firefox and Eclipse running.

Does /proc/cpuinfo reflect a possible automatic downclock made to save power if processor load is low or is this output abnormal?

EDIT: Ok, I checked and yes, the ouput does vary in function of the load. I reach 2.2 GHz when needed. But my following problem remains.

I was checking my CPU clocking because I experienced poor performances when reading 720p video files on Ubuntu with VLC or mplayer when on battery (and I believe VLC by default only uses CPU, not GPU to decode), whereas I haven't got such problems with VLC on Windows (which made me think it wasn't coming from a BIOS option, plus every option in the BIOS regarding the CPU is turned ON).

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1 Answer 1

Yes, almost all Intel CPUs made in the last decade or so can vary their clock speeds according to the load, and the default "frequency scaling governor" is the "on demand" governor, which keeps the CPUs at minimum speed until they are needed, at which point it immediately switches them to maximum frequency.

You can keep track of the changing frequencies by using the following command: watch -p -n1 'cat /proc/cpuinfo | grep -i "hz"'. That will report the current CPU frequencies every second. Try running that in a terminal and then starting up a video in VLC while watching how the frequencies change. You can see if the poor performance correlates with the CPUs being downclocked inappropriately, but I doubt that is the real problem.

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Well actually it gives something: when on battery, the frequencies stay pretty much around 800MHz when I read a video, whereas when AC adapter is plugged in the're not capped, I can see cores at 2,2GHz. –  Ywen Apr 6 '12 at 7:17
    
And when I deactivate the Intel SpeedStep option in the BIOS, thus forcing cores to be at full speed at every time, it works. –  Ywen Apr 6 '12 at 7:40
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