Messages in this thread Patch in this message | | | Date | Wed, 19 Feb 2020 09:08:22 +0000 | From | Mel Gorman <> | Subject | Re: [PATCH v2 4/5] sched/pelt: Add a new runnable average signal |
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On Tue, Feb 18, 2020 at 09:19:16PM +0000, Valentin Schneider wrote: > On 14/02/2020 15:27, Vincent Guittot wrote: > > Now that runnable_load_avg has been removed, we can replace it by a new > > signal that will highlight the runnable pressure on a cfs_rq. This signal > > track the waiting time of tasks on rq and can help to better define the > > state of rqs. > > > > At now, only util_avg is used to define the state of a rq: > > A rq with more that around 80% of utilization and more than 1 tasks is > > considered as overloaded. > > > > But the util_avg signal of a rq can become temporaly low after that a task > > migrated onto another rq which can bias the classification of the rq. > > > > When tasks compete for the same rq, their runnable average signal will be > > higher than util_avg as it will include the waiting time and we can use > > this signal to better classify cfs_rqs. > > > > The new runnable_avg will track the runnable time of a task which simply > > adds the waiting time to the running time. The runnable _avg of cfs_rq > > will be the /Sum of se's runnable_avg and the runnable_avg of group entity > > will follow the one of the rq similarly to util_avg. > > > > I did a bit of playing around with tracepoints and it seems to be behaving > fine. For instance, if I spawn 12 always runnable tasks (sysbench --test=cpu) > on my Juno (6 CPUs), I get to a system-wide runnable value (\Sum cpu_runnable()) > of about 12K. I've only eyeballed them, but migration of the signal values > seem fine too. > > I have a slight worry that the rq-wide runnable signal might be too easy to > inflate, since we aggregate for *all* runnable tasks, and that may not play > well with your group_is_overloaded() change (despite having the imbalance_pct > on the "right" side). > > In any case I'll need to convince myself of it with some messing around, and > this concerns patch 5 more than patch 4. So FWIW for this one: > > Tested-by: Valentin Schneider <valentin.schneider@arm.com> > > I also have one (two) more nit(s) below. >
Thanks.
> > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > > --- > > diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c > > @@ -227,14 +231,14 @@ ___update_load_sum(u64 now, struct sched_avg *sa, > > * Step 1: accumulate *_sum since last_update_time. If we haven't > > * crossed period boundaries, finish. > > */ > > - if (!accumulate_sum(delta, sa, load, running)) > > + if (!accumulate_sum(delta, sa, load, runnable, running)) > > return 0; > > > > return 1; > > } > > > > static __always_inline void > > -___update_load_avg(struct sched_avg *sa, unsigned long load) > > +___update_load_avg(struct sched_avg *sa, unsigned long load, unsigned long runnable) > > { > > u32 divider = LOAD_AVG_MAX - 1024 + sa->period_contrib; > > > > @@ -242,6 +246,7 @@ ___update_load_avg(struct sched_avg *sa, unsigned long load) > > * Step 2: update *_avg. > > */ > > sa->load_avg = div_u64(load * sa->load_sum, divider); > > + sa->runnable_avg = div _u64(runnable * sa->runnable_sum, divider); > ^^^^^^ ^^^^^^^^ > a) b) > a) That's a tab >
Fixed and I'll post a v4 of my own series with Vincent's included.
> b) The value being passed is always 1, do we really need it to expose it as a > parameter?
This does appear to be an oversight but I'm not familiar enough with pelt to be sure.
___update_load_avg() is called when sum of the load has changed because a pelt period has passed and it has lost sight and does not care if an individual sched entity is runnable or not. The parameter was added by this patch but I cannot find any useful meaning for it.
Vincent, what was your thinking here? Should the parameter be removed?
-- Mel Gorman SUSE Labs
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