Messages in this thread | | | Date | Mon, 22 Aug 2016 12:29:25 +0100 | From | Morten Rasmussen <> | Subject | Re: [PATCH v3 10/13] sched/fair: Compute task/cpu utilization at wake-up more correctly |
| |
On Mon, Aug 22, 2016 at 09:48:19AM +0800, Wanpeng Li wrote: > 2016-08-19 22:03 GMT+08:00 Morten Rasmussen <morten.rasmussen@arm.com>: > > On Fri, Aug 19, 2016 at 09:43:00AM +0800, Wanpeng Li wrote: > >> 2016-08-18 21:45 GMT+08:00 Morten Rasmussen <morten.rasmussen@arm.com>: > >> > I assume you are referring to using task_util_peak() instead of > >> > task_util() in wake_cap()? > >> > >> Yes. > >> > >> > > >> > The peak value should never exceed the util_avg accumulated by the task > >> > last time it ran. So any spike has to be caused by the task accumulating > >> > more utilization last time it ran. We don't know if it a spike or a more > >> > >> I see. > >> > >> > permanent change in behaviour, so we have to guess. So a spike on an > >> > asymmetric system could cause us to disable wake affine in some > >> > circumstances (either prev_cpu or waker cpu has to be low compute > >> > capacity) for the following wake-up. > >> > > >> > SMP should be unaffected as we should bail out on the previous > >> > condition. > >> > >> Why capacity_orig instead of capacity since it is checked each time > >> wakeup and maybe rt class/interrupt have already occupied many cpu > >> utilization. > > > > We could switch to capacity for this condition if we also change the > > spare capacity evaluation in find_idlest_group() to do the same. It > > would open up for SMP systems to take find_idlest_group() route if the > > SD_BALANCE_WAKE flag is set. > > > > The reason why I have avoided capacity and used capacity_orig instead > > is that in previous discussions about scheduling behaviour under > > rt/dl/irq pressure it has been clear to me whether we want to move tasks > > away from cpus with capacity < capacity_orig or not. The choice depends > > on the use-case. > > > > In some cases taking rt/dl/irq pressure into account is more complicated > > as we don't know the capacities available in a sched_group without > > iterating over all the cpus. However, I don't think it would complicate > > these patches. It is more a question whether everyone are happy with > > additional conditions in their wake-up path. I guess we could make it a > > sched_feature if people are interested? > > > > In short, I used capacity_orig to play it safe ;-) > > Actually you mixed capacity_orig and capacity when evaluating max spare cap.
Right, that is a mistake. Thanks for pointing that out :-)
Morten
| |