Messages in this thread | | | From | Vincent Guittot <> | Date | Thu, 9 Aug 2018 18:03:57 +0200 | Subject | Re: [PATCH v3 06/14] sched/cpufreq: uclamp: add utilization clamping for RT tasks |
| |
Hi Patrick,
On Thu, 9 Aug 2018 at 17:34, Patrick Bellasi <patrick.bellasi@arm.com> wrote: > > On 07-Aug 15:26, Juri Lelli wrote: > > Hi, > > > > On 06/08/18 17:39, Patrick Bellasi wrote: > > > > [...] > > > > > @@ -223,13 +224,25 @@ static unsigned long sugov_get_util(struct sugov_cpu *sg_cpu) > > > * utilization (PELT windows are synchronized) we can directly add them > > > * to obtain the CPU's actual utilization. > > > * > > > - * CFS utilization can be boosted or capped, depending on utilization > > > - * clamp constraints configured for currently RUNNABLE tasks. > > > + * CFS and RT utilizations can be boosted or capped, depending on > > > + * utilization constraints enforce by currently RUNNABLE tasks. > > > + * They are individually clamped to ensure fairness across classes, > > > + * meaning that CFS always gets (if possible) the (minimum) required > > > + * bandwidth on top of that required by higher priority classes. > > > > Is this a stale comment written before UCLAMP_SCHED_CLASS was > > introduced? It seems to apply to the below if branch only. > > Yes, you right... I'll update the comment. > > > > */ > > > - util = cpu_util_cfs(rq); > > > - if (util) > > > - util = uclamp_util(cpu_of(rq), util); > > > - util += cpu_util_rt(rq); > > > + 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()
> > We had an internal discussion and we found pro/cons for both... but > I'm not sure keeping the sched_feat is a good solution on the long > run, i.e. mainline merge ;) > > -- > #include <best/regards.h> > > Patrick Bellasi
| |