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

Vincent Guittot
2016-03-31T09:27:46Z

On 30 March 2016 at 21:35, Peter Zijlstra <peterz@infradead.org> wrote:
> 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.

Isn't a reschedule ipi already sent in this case ?