Mailinglist Archive: opensuse (729 mails)

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Re: [opensuse] CPU speed
On 06/03/2015 01:25 AM, Roger Oberholtzer wrote:
I have a system (not a laptop) that has an "AMD Phenom(tm) II X6 1100T
Processor", as reported in /proc/cpuinfo. I have been monitoring the
CPU speed as reported there and I see that quite often the speed is
reported as 800 MHz instead of 3300 MHz. For example, I ran the four
commands pretty much one after the other. The speed is changing all
the time:

roger@acme:~> cat /proc/cpuinfo | grep "cpu MHz"
cpu MHz : 3300.000
cpu MHz : 3300.000
cpu MHz : 800.000
cpu MHz : 3300.000
cpu MHz : 3300.000
cpu MHz : 3300.000
roger@acme:~> cat /proc/cpuinfo | grep "cpu MHz"
cpu MHz : 800.000
cpu MHz : 3300.000
cpu MHz : 3300.000
cpu MHz : 800.000
cpu MHz : 3300.000
cpu MHz : 3300.000
roger@acme:~> cat /proc/cpuinfo | grep "cpu MHz"
cpu MHz : 800.000
cpu MHz : 800.000
cpu MHz : 800.000
cpu MHz : 800.000
cpu MHz : 3300.000
cpu MHz : 3300.000
roger@acme:~> cat /proc/cpuinfo | grep "cpu MHz"
cpu MHz : 800.000
cpu MHz : 2500.000
cpu MHz : 3300.000
cpu MHz : 800.000
cpu MHz : 3300.000
cpu MHz : 3300.000

The system is busy when this is run. So I cannot think there are
unused CPUs that are made to slow down because they have nothing to
do. Especially changing as often as they seem to be changing.

Is this expected behavior?


Totally normal.
As for the system being "busy", you have to realize that
tasks don't necessarily jump from CPU to CPU on a whim, and
constantly bouncing tasks to different CPUs that are perceived
as running slowly does not improve performance nor power saving.
Tasks can't always make use of multiple cores. A great deal of code
is single threaded over large sections, which means another idle core
can't necessarily be pressed into service.

Besides, your instantaneous reading is not indicative of anything in particular.

My recommendation is to STOP watching this.

It will drive you to micromanaging the cpu speed, which, with all due respect,
you are poorly
equipped to do. The kernel's scheduler is way better at this than you will ever
be.

The only conclusion you can draw is your machine is far less busy than you
think.

If you have some specific problem you are trying to solve, let us know that it
is. If the machine is running slowly in your opinion, look into the power
profile
and set it to high performance.

Other than that, the breakfast sausage tastes much better if you don't
watch how it is made.


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