Re: [PATCH 1/2] sched/fair: move cpufreq hook to update_cfs_rq_load_avg()

Peter Zijlstra
2016-03-30T19:35:55Z

On Mon, Mar 28, 2016 at 12:38:26PM -0700, Steve Muckle wrote:
> Without covering all the paths where CFS utilization changes it's
> possible to have to wait up to a tick to act on some changes, since the
> tick is the only guaranteed regularly-occurring instance of the hook.
> That's an unacceptable amount of latency IMO...

Note that even with your patches that might still be the case. Remote
wakeups might not happen on the destination CPU at all, so it might not
be until the next tick (which always happens locally) that we'll
'observe' the utilization change brought with the wakeups.

We could force all the remote wakeups to IPI the destination CPU, but
that comes at a significant performance cost.