cpuset configuration and measurements for power management

[Vincent Guittot]

On 23 August 2011 14:41, Daniel Lezcano <daniel.lezcano at linaro.org> wrote:
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> Hi all,
>
> I did the following cpuset configuration:
>
> if [ ! -d /sys/fs/cgroup ]; then
>        echo "cgroup not supported by the kernel"
> else
>        mount -t cgroup cgroup /sys/fs/cgroup
>
>        # needed to have the cgroup values inherited from
>        # the parent cgroup
>        echo 1 > /sys/fs/cgroup/cgroup.clone_children
>
>        # create an empty cgroup 'cpu0'
>        mkdir /sys/fs/cgroup/cpu0
>
>        # create an empty cgroup 'cpu1'
>        mkdir /sys/fs/cgroup/cpu1
>
>        # assign cpu number '0' for cgroup cpu0
>        echo 0 > /sys/fs/cgroup/cpu0/cpuset.cpus
>
>        # move outself to this new cgroup
>        echo $$ > /sys/fs/cgroup/cpu0
>
>        # move all the tasks to the cpu0 cgroup
>        # kernel threads won't be moved, don't worry about the
>        # the errors.
>        for i in $(cat /sys/fs/cgroup/tasks); do
>                echo $i > /sys/fs/cgroup/cpu0/tasks || echo "failed to
> add pid $i/$(cat /proc/$i/comm)"
>        done
>
>        # assign a cpu for cgroup cpu1
>        echo 1 > /sys/fs/cgroup/cpu1/cpuset.cpus
>
>        # make cpu1 exclusive so processes belonging
>        # to the other cgroups won't be able to use it.
>        echo 1 > /sys/fs/cgroup/cpu1/cpuset.cpu_exclusive
> fi
>
>
> At this point, most of the processes have been moved to the 'cpu0'
> cgroup and will use the cpu0 only. That does not prevent the cpu1 to be
> used by the kernel threads. Any application launched will run on cpu0 only.
>
> After running 10 infinite loops, the cpu accounting gives:
>
> cat /sys/fs/cgroup/cpu0/cpuacct.usage_percpu
> 418943579549 0
>
> cat /sys/fs/cgroup/cpu1/cpuacct.usage_percpu
> 0 0
>
> But the system is:
>
> cat /sys/fs/cgroup/cpuacct.usage_percpu
> 456741213041 30734572583
>

You should get the values before and after your tests and compute the
difference. You should also read value of  /sys/fs/cgroup/ level where
we still have kernel threads if i have understand your comments

> My guess is that reflects the kernel booted with the two cpus before we
> created the cgroup. I am investigation the 'isolcpus' kernel parameter.
>
> I think it is a good starting point to do some consumption measurements.
>
> Mike, Vincent, what do you think ? Do you need more informations or
> anything else ?
>

Yes it's a good starting point. One key point will be to be sure to
not use cpu1. In fact, we mainly have 2 power efficient states:  use
equally the 2 cpus or use only one cpu and put the other one in a low
power state.

Vincent

> Thanks
>  -- Daniel
>
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