Messages in this thread | | | Date | Wed, 31 May 2017 12:30:17 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH 1/2] sched/rt: add utilization tracking |
| |
On Wed, May 31, 2017 at 11:40:47AM +0200, Peter Zijlstra wrote: > On Wed, May 24, 2017 at 11:00:51AM +0200, Vincent Guittot wrote: > > schedutil governor relies on cfs_rq's util_avg to choose the OPP when cfs > > tasks are running. When the CPU is overloaded by cfs and rt tasks, cfs tasks > > are preempted by rt tasks and in this case util_avg reflects the remaining > > capacity that is used by cfs tasks but not what cfs tasks want to use. In such > > case, schedutil can select a lower OPP when cfs task runs whereas the CPU is > > overloaded. In order to have a more accurate view of the utilization of the > > CPU, we track the utilization that is used by RT tasks. > > DL tasks are not taken into account as they have their own utilization > > tracking mecanism. > > Well, the DL tracking is fairly pessimistic; it assumes all DL tasks > will consume their total budget, which will rarely, if ever, happen. > > So I suspect it might well be worth it to also track DL activity for the > purpose of compensating CFS.
Again, it seems I have this CPPC/HWP crud firmly stuck in my brain. Because I was thinking:
min_freq = dl_util avg_freq = dl_avg + rt_avg + cfs_util
But given we don't actually have that split... meh.
> In fact, I don't think you particularly care about RT here, as anything > !CFS that preempts it, including those interrupts you mentioned. Which > gets us back to what rt_avg is. > > > We don't use rt_avg which doesn't have the same dynamic as PELT and which > > can include IRQ time that are also accounted in cfs task utilization > > Well, if rt_avg includes IRQ time, then that IRQ time is not part of > the task clock.
| |