Re: cputime takes cstate into consideration

[Peter Zijlstra]

On Wed, Jun 26, 2019 at 05:43:55PM +0800, Wanpeng Li wrote:
> Hi all,
> 
> After exposing mwait/monitor into kvm guest, the guest can make
> physical cpu enter deeper cstate through mwait instruction, however,
> the top command on host still observe 100% cpu utilization since qemu
> process is running even though guest who has the power management
> capability executes mwait. Actually we can observe the physical cpu
> has already enter deeper cstate by powertop on host. Could we take
> cstate into consideration when accounting cputime etc?

Either we account runtime on the CPU itself, in which case it will not
be in a C state due to actually running an interrupt that does
accounting, or we do it remote (NOHZ_FULL case) and there is no way to
know what C state, if any, that CPU is in.