Messages in this thread | | | Date | Wed, 6 Sep 2023 14:56:20 +0200 | Subject | Re: [RFC PATCH 1/7] sched/pelt: Add a new function to approximate the future util_avg value | From | Dietmar Eggemann <> |
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On 28/08/2023 01:31, Qais Yousef wrote: > Given a util_avg value, the new function will return the future one > given a runtime delta. > > This will be useful in later patches to help replace some magic margins > with more deterministic behavior. > > Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io> > --- > kernel/sched/pelt.c | 22 +++++++++++++++++++++- > kernel/sched/sched.h | 3 +++ > 2 files changed, 24 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c > index 0f310768260c..50322005a0ae 100644 > --- a/kernel/sched/pelt.c > +++ b/kernel/sched/pelt.c > @@ -466,4 +466,24 @@ int update_irq_load_avg(struct rq *rq, u64 running) > > return ret; > } > -#endif > +#endif /* CONFIG_HAVE_SCHED_AVG_IRQ */ > + > +/* > + * Approximate the new util_avg value assuming an entity has continued to run > + * for @delta us. > + */ > +unsigned long approximate_util_avg(unsigned long util, u64 delta) > +{ > + struct sched_avg sa = { > + .util_sum = util * PELT_MIN_DIVIDER, > + .util_avg = util, > + }; > + > + if (unlikely(!delta)) > + return util; > + > + accumulate_sum(delta, &sa, 0, 0, 1);
IMHO, you miss the handling of `periods != 0`. load = 0 eclipses this code in accumulate_sum().
> + ___update_load_avg(&sa, 0); > + > + return sa.util_avg; > +}
We already discussed something similar like this in Nov 22, the so called UTIL_EST_FASTER thing.
https://lkml.kernel.org/r/Y2kLA8x40IiBEPYg@hirez.programming.kicks-ass.net
+/* + * Compute a pelt util_avg assuming no history and @delta runtime. + */ +unsigned long faster_est_approx(u64 delta) +{ + unsigned long contrib = (unsigned long)delta; /* p == 0 -> delta < 1024 */ + u64 periods = delta / 1024; + + if (periods) { + delta %= 1024; + contrib = __accumulate_pelt_segments(periods, 1024, delta); + } + + return (contrib << SCHED_CAPACITY_SHIFT) / PELT_MIN_DIVIDER; +} +
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