[Query-CPUIdle]: Not much activity in C0 state

[Query-CPUIdle]: Not much activity in C0 state

[Viresh Kumar]

Hi Guys,

I was trying to run following on my thinkpad:

watch -n1 cat /sys/devices/system/cpu/cpu*/cpuidle/state*/usage

I can see lots of activities on State 1-4, but not much on state 0..
I thought we should enter this state as soon as we come out to
non-idle state.. And so this count must be changing quite rapidly.

Is this a bug?

--
viresh

Re: [Query-CPUIdle]: Not much activity in C0 state

[Daniel Lezcano]

On 08/27/2013 12:23 PM, Viresh Kumar wrote:
> Hi Guys,
> 
> I was trying to run following on my thinkpad:
> 
> watch -n1 cat /sys/devices/system/cpu/cpu*/cpuidle/state*/usage
> 
> I can see lots of activities on State 1-4, but not much on state 0..
> I thought we should enter this state as soon as we come out to
> non-idle state.. And so this count must be changing quite rapidly.
> 
> Is this a bug?

Hi Viresh,

the menu governor tries always to stick to C1 (state1) as default state,
look at the menu_select function. The state0 (not C0 but 'poll') will
happen when the next timer event is less than 5us, this occurs rarely.
You can easily spot it by doing while $(true); usleep 2; done

The poll state is x86 specific where the cpu detects the 'rep nop'
instructions to do some power saving.

Hope that helps

  -- Daniel



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