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

Peter Zijlstra
2016-03-31T10:47:10Z

On Thu, Mar 31, 2016 at 11:50:40AM +0200, Vincent Guittot wrote:
> > In what case? Assuming you talk about a remove wakeup, no. Only if that
> > wakeup results in a preemption, which isn't a given.
>
> yes, i was speaking about a remote wakeup.
> In the ttwu_queue_remote, there is a call to smp_send_reschedule. Is
> there another way to add a remote task in the wake list ?

Right, but at that point we don't yet know how much util will change.

And doing that IPI unconditionally is expensive; see:

518cd6234178 ("sched: Only queue remote wakeups when crossing cache boundaries")

13% regression on TCP_RR.