Messages in this thread | | | Subject | Re: [PATCH v5 07/10] sched/irq: add irq utilization tracking | From | Dietmar Eggemann <> | Date | Wed, 30 May 2018 17:55:24 +0200 |
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On 05/25/2018 03:12 PM, Vincent Guittot wrote: > interrupt and steal time are the only remaining activities tracked by > rt_avg. Like for sched classes, we can use PELT to track their average > utilization of the CPU. But unlike sched class, we don't track when > entering/leaving interrupt; Instead, we take into account the time spent > under interrupt context when we update rqs' clock (rq_clock_task). > This also means that we have to decay the normal context time and account > for interrupt time during the update. > > That's also important to note that because > rq_clock == rq_clock_task + interrupt time > and rq_clock_task is used by a sched class to compute its utilization, the > util_avg of a sched class only reflects the utilization of the time spent > in normal context and not of the whole time of the CPU. The utilization of > interrupt gives an more accurate level of utilization of CPU. > The CPU utilization is : > avg_irq + (1 - avg_irq / max capacity) * /Sum avg_rq > > Most of the time, avg_irq is small and neglictible so the use of the > approximation CPU utilization = /Sum avg_rq was enough
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> @@ -7362,6 +7363,7 @@ static void update_blocked_averages(int cpu) > } > update_rt_rq_load_avg(rq_clock_task(rq), rq, 0); > update_dl_rq_load_avg(rq_clock_task(rq), rq, 0); > + update_irq_load_avg(rq, 0);
So this one decays the signals only in case the update_rq_clock_task() didn't call update_irq_load_avg() because 'irq_delta + steal' is 0, right?
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> diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c > index 3d5bd3a..d2e4f21 100644 > --- a/kernel/sched/pelt.c > +++ b/kernel/sched/pelt.c > @@ -355,3 +355,41 @@ int update_dl_rq_load_avg(u64 now, struct rq *rq, int running) > > return 0; > } > + > +/* > + * irq: > + * > + * util_sum = \Sum se->avg.util_sum but se->avg.util_sum is not tracked > + * util_sum = cpu_scale * load_sum > + * runnable_load_sum = load_sum > + * > + */ > + > +int update_irq_load_avg(struct rq *rq, u64 running) > +{ > + int ret = 0; > + /* > + * We know the time that has been used by interrupt since last update > + * but we don't when. Let be pessimistic and assume that interrupt has > + * happened just before the update. This is not so far from reality > + * because interrupt will most probably wake up task and trig an update > + * of rq clock during which the metric si updated. > + * We start to decay with normal context time and then we add the > + * interrupt context time. > + * We can safely remove running from rq->clock because > + * rq->clock += delta with delta >= running
This is true as long update_irq_load_avg() with a 'running != 0' is called only after rq->clock moved forward (rq->clock += delta) (which is true for update_rq_clock()->update_rq_clock_task()).
> + */ > + ret = ___update_load_sum(rq->clock - running, rq->cpu, &rq->avg_irq, > + 0, > + 0, > + 0); > + ret += ___update_load_sum(rq->clock, rq->cpu, &rq->avg_irq, > + 1, > + 1, > + 1);
So you decay the signal in [sa->lut, rq->clock - running] (assumed to be the portion of delta used by the task scheduler) and you increase it in [rq->clock - running, rq->clock] (irq and virt portion of delta).
That means that this signal is updated on rq->clock whereas the others are on rq->clock_task.
What about the ever growing clock diff between them? I see e.g ~6s after 20min uptime and up to 1.5ms 'running'.
It should be still safe to sum the sched class and irq signal in sugov_aggregate_util() because they are independent, I guess.
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