Messages in this thread | | | Date | Fri, 22 Jun 2018 09:58:17 +0200 | From | Juri Lelli <> | Subject | Re: [PATCH v6 04/11] cpufreq/schedutil: use rt utilization tracking |
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On 21/06/18 20:45, Peter Zijlstra wrote: > On Fri, Jun 08, 2018 at 02:09:47PM +0200, Vincent Guittot wrote: > > static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu) > > { > > struct rq *rq = cpu_rq(sg_cpu->cpu); > > + unsigned long util; > > > > if (rq->rt.rt_nr_running) > > return sg_cpu->max; > > > > + util = sg_cpu->util_dl; > > + util += sg_cpu->util_cfs; > > + util += sg_cpu->util_rt; > > + > > /* > > * Utilization required by DEADLINE must always be granted while, for > > * FAIR, we use blocked utilization of IDLE CPUs as a mechanism to > > @@ -197,7 +204,7 @@ static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu) > > * util_cfs + util_dl as requested freq. However, cpufreq is not yet > > * ready for such an interface. So, we only do the latter for now. > > */ > > - return min(sg_cpu->max, (sg_cpu->util_dl + sg_cpu->util_cfs)); > > + return min(sg_cpu->max, util); > > } > > So this (and the dl etc. equivalents) result in exactly the problems > complained about last time, no? > > What I proposed was something along the lines of: > > util = 1024 * sg_cpu->util_cfs; > util /= (1024 - (sg_cpu->util_rt + sg_cpu->util_dl + ...)); > > return min(sg_cpu->max, util + sg_cpu->bw_dl); > > Where we, instead of directly adding the various util signals. > > I now see an email from Quentin asking if these things are not in fact > the same, but no, they are not. The difference is that the above only > affects the CFS signal and will re-normalize the utilization of an > 'always' running task back to 1 by compensating for the stolen capacity. > > But it will not, like these here patches, affect the OPP selection of > other classes. If there is no CFS utilization (or very little), then the > renormalization will not matter, and the existing DL bandwidth > compuation will be unaffected.
IIUC, even with very little CFS utilization, the final OPP selection will still be "inflated" w.r.t. bw_dl in case util_dl is big (like for a DL task with a big period and not so big runtime). But I guess that's OK, since we agreed that such DL tasks should be the exception anyway.
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