Messages in this thread Patch in this message | | | Date | Fri, 16 Dec 2022 15:24:06 -0800 | From | Ricardo Neri <> | Subject | Re: [PATCH v2 09/22] sched/fair: Use IPC class score to select a busiest runqueue |
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On Wed, Dec 14, 2022 at 11:16:39PM +0000, Ionela Voinescu wrote: > Hi Ricardo, > > On Tuesday 13 Dec 2022 at 16:32:43 (-0800), Ricardo Neri wrote: > [..] > > > > /** > > > > @@ -10419,8 +10442,8 @@ static struct rq *find_busiest_queue(struct lb_env *env, > > > > { > > > > struct rq *busiest = NULL, *rq; > > > > unsigned long busiest_util = 0, busiest_load = 0, busiest_capacity = 1; > > > > + int i, busiest_ipcc_delta = INT_MIN; > > > > unsigned int busiest_nr = 0; > > > > - int i; > > > > > > > > for_each_cpu_and(i, sched_group_span(group), env->cpus) { > > > > unsigned long capacity, load, util; > > > > @@ -10526,8 +10549,37 @@ static struct rq *find_busiest_queue(struct lb_env *env, > > > > > > > > case migrate_task: > > > > if (busiest_nr < nr_running) { > > > > + struct task_struct *curr; > > > > + > > > > busiest_nr = nr_running; > > > > busiest = rq; > > > > + > > > > + /* > > > > + * Remember the IPC score delta of busiest::curr. > > > > + * We may need it to break a tie with other queues > > > > + * with equal nr_running. > > > > + */ > > > > + curr = rcu_dereference(busiest->curr); > > > > + busiest_ipcc_delta = ipcc_score_delta(curr, > > > > + env->dst_cpu); > > > > + /* > > > > + * If rq and busiest have the same number of running > > > > + * tasks, pick rq if doing so would give rq::curr a > > > > + * bigger IPC boost on dst_cpu. > > > > + */ > > > > + } else if (sched_ipcc_enabled() && > > > > + busiest_nr == nr_running) { > > > > + struct task_struct *curr; > > > > + int delta; > > > > + > > > > + curr = rcu_dereference(rq->curr); > > > > + delta = ipcc_score_delta(curr, env->dst_cpu); > > > > + > > > > + if (busiest_ipcc_delta < delta) { > > > > + busiest_ipcc_delta = delta; > > > > + busiest_nr = nr_running; > > > > + busiest = rq; > > > > + } > > > > } > > > > break; > > > > > > > > > > While in the commit message you describe this as breaking a tie for > > > asym_packing, > > > > Are you referring to the overall series or this specific patch? I checked > > commit message and I do not see references to asym_packing. > > Sorry, my bad, I was thinking about the cover letter, not the commit > message. It's under "+++ Balancing load using classes of tasks. Theory > of operation". > > > > > > the code here does not only affect asym_packing. If > > > another architecture would have sched_ipcc_enabled() it would use this > > > as generic policy, and that might not be desired. > > > > Indeed, the patchset implements support to use IPCC classes for asym_packing, > > but it is not limited to it. > > > > So is your current intention to support IPC classes only for asym_packing > for now?
My intention is to introduce IPC classes in general and make it available to other policies or architectures. I use asym_packing as use case.
> What would be the impact on you if you were to limit the > functionality in this patch to asym_packing only?
There would not be any adverse impact.
> > > It is true that I don't check here for asym_packing, but it should not be a > > problem, IMO. I compare two runqueues with equal nr_running, either runqueue > > is a good choice. This tie breaker is an overall improvement, no? > > > > It could be, but equally there could be other better policies as well - > other ways to consider IPC class information to break the tie. > > If other architectures start having sched_ipcc_enabled() they would > automatically use the policy you've decided on here. If other policies > are better for those architectures this generic policy would be difficult > to modify to ensure there are no regressions for all other architectures > that use it, or it would be difficult to work around it. > > For this and for future support of IPC classes I am just wondering if we > can better design how we enable different architectures to have different > policies.
I see your point. I agree that other architectures may want to implement policies differently. I'll add an extra check for env->sd & SD_ASYM_PACKING.
Thanks and BR, Ricardo
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