Messages in this thread | | | Date | Fri, 22 Dec 2017 14:01:18 +0100 | From | Juri Lelli <> | Subject | Re: [PATCH v3 0/6] cpufreq: schedutil: fixes for flags updates |
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On 22/12/17 12:50, Patrick Bellasi wrote: > On 22-Dec 13:43, Juri Lelli wrote: > > On 22/12/17 12:38, Patrick Bellasi wrote: > > > On 22-Dec 13:19, Peter Zijlstra wrote: > > > > On Fri, Dec 22, 2017 at 12:07:37PM +0000, Patrick Bellasi wrote: > > > > > > I was thinking that since dl is a 'global' scheduler the reservation > > > > > > would be too and thus the freq just needs a single CPU to be observed; > > > > > > > > > > AFAIU global is only the admission control (which is something worth a > > > > > thread by itself...) while the dl_se->dl_bw are aggregated into the > > > > > dl_rq->running_bw, which ultimately represents the DL bandwidth > > > > > required for just a CPU. > > > > > > > > Oh urgh yes, forgot that.. then the dl freq stuff isn't strictly correct > > > > I think. But yes, that's another thread. > > > > > > Mmm... maybe I don't get your point... I was referring to the global > > > admission control of DL. If you have for example 3 60% DL tasks on a > > > 2CPU system, AFAIU the CBS will allow the tasks in the system (since > > > the overall utilization is 180 < 200 * 0.95) although that workload is > > > not necessarily schedule (for example if the tasks wakeups at the > > > same time one of them will miss its deadline). > > > > > > But, yeah... maybe I'm completely wrong or, in any case, it's for a > > > different thread... > > > > > > > > > but I suppose there's nothing stopping anybody from splitting a clock > > > > > > domain down the middle scheduling wise. So yes, good point. > > > > > > > > > > That makes sense... moreover, using the global utilization, we would > > > > > end up asking for capacities which cannot be provided by a single CPU. > > > > > > > > Yes, but that _should_ not be a problem if you clock them all high > > > > enough. But this gets to be complicated real fast I think. > > > > > > IMO the current solution with Juri's patches is working as expected: > > > we know how many DL tasks are runnable on a CPU and we properly > > > account for their utilization. > > > > > > The only "issue/limitation" is (eventually) the case described above. > > > Dunno if we can enqueue 2 60% DL tasks on the same CPU... in that case > > > we will ask for 120% Utilization? > > > > In general it depends on the other parameters, deadline and period. > > Right, but what about the case dealdine==period, with 60% utilization? > AFAIU, 3 DL tasks with same parameters like above will be accepted on > a 2 CPU system, isn't it? > > And thus, in that case, we can end up with a 120% utlization request > from DL for a single CPU... but, considering it's lunch o'clock, > I'm likely missing something...
Nope. CBS on SMP only gives you bounded tardiness (at least with the AC kernel does). Some deadlines might be missed.
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