Messages in this thread |  | | Date | Mon, 13 Aug 2018 12:50:34 +0200 | From | Juri Lelli <> | Subject | Re: [PATCH v3 06/14] sched/cpufreq: uclamp: add utilization clamping for RT tasks |
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On 13/08/18 11:12, Patrick Bellasi wrote: > Hi Vincent! > > On 09-Aug 18:03, Vincent Guittot wrote: > > > On 07-Aug 15:26, Juri Lelli wrote: > > [...] > > > > > > + util_cfs = cpu_util_cfs(rq); > > > > > + util_rt = cpu_util_rt(rq); > > > > > + if (sched_feat(UCLAMP_SCHED_CLASS)) { > > > > > + util = 0; > > > > > + if (util_cfs) > > > > > + util += uclamp_util(cpu_of(rq), util_cfs); > > > > > + if (util_rt) > > > > > + util += uclamp_util(cpu_of(rq), util_rt); > > > > > + } else { > > > > > + util = cpu_util_cfs(rq); > > > > > + util += cpu_util_rt(rq); > > > > > + util = uclamp_util(cpu_of(rq), util); > > > > > + } > > > > > > Regarding the two policies, do you have any comment? > > > > Does the policy for (sched_feat(UCLAMP_SCHED_CLASS)== true) really > > make sense as it is ? > > I mean, uclamp_util doesn't make any difference between rt and cfs > > tasks when clamping the utilization so why should be add twice the > > returned value ? > > IMHO, this policy would make sense if there were something like > > uclamp_util_rt() and a uclamp_util_cfs() > > The idea for the UCLAMP_SCHED_CLASS policy is to improve fairness on > low-priority classese, especially when we have high RT utilization. > > Let say we have: > > util_rt = 40%, util_min=0% > util_cfs = 10%, util_min=50% > > the two policies will select: > > UCLAMP_SCHED_CLASS: util = uclamp(40) + uclamp(10) = 50 + 50 = 100% > !UCLAMP_SCHED_CLASS: util = uclamp(40 + 10) = uclmp(50) = 50% > > Which means that, despite the CPU's util_min will be set to 50% when > CFS is running, these tasks will have almost no boost at all, since > their bandwidth margin is eclipsed by RT tasks.
Ah, right. But isn't possible to distinguish between classes? I mean, if you would know that only CFS is clamped (boosted) in this case, you could have:
util = util_rt + uclamp(util_cfs) = 40 + 50 = 90%
Which should do what one expects w/o energy side effects?
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