Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 31 Mar 2023 14:23:58 +0200 | Subject | Re: [PATCH v3 10/24] sched/fair: Use IPCC scores to select a busiest runqueue |
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On Thu, 30 Mar 2023 at 04:03, Ricardo Neri <ricardo.neri-calderon@linux.intel.com> wrote: > > On Tue, Mar 28, 2023 at 12:03:58PM +0200, Vincent Guittot wrote: > > On Tue, 7 Feb 2023 at 06:01, Ricardo Neri > > <ricardo.neri-calderon@linux.intel.com> wrote: > > > > > > For two runqueues of equal priority and equal number of running of tasks, > > > select the one whose current task would have the highest IPC class score > > > if placed on the destination CPU. > > > > You failed to explain why it make sense to compare current task score > > whereas we will most probably not pull this task at the end > > Thank you for your feedback Vincent! Please kindly refer to my reply to > your feedback in patch 7. > > > > > > > For now, use IPCC scores only for scheduling domains with the > > > SD_ASYM_PACKING flag. > > > > > > Cc: Ben Segall <bsegall@google.com> > > > Cc: Daniel Bristot de Oliveira <bristot@redhat.com> > > > Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> > > > Cc: Ionela Voinescu <ionela.voinescu@arm.com> > > > Cc: Joel Fernandes (Google) <joel@joelfernandes.org> > > > Cc: Len Brown <len.brown@intel.com> > > > Cc: Lukasz Luba <lukasz.luba@arm.com> > > > Cc: Mel Gorman <mgorman@suse.de> > > > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > > Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> > > > Cc: Steven Rostedt <rostedt@goodmis.org> > > > Cc: Tim C. Chen <tim.c.chen@intel.com> > > > Cc: Valentin Schneider <vschneid@redhat.com> > > > Cc: x86@kernel.org > > > Cc: linux-pm@vger.kernel.org > > > Cc: linux-kernel@vger.kernel.org > > > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com> > > > --- > > > Changes since v2: > > > * Only use IPCC scores to break ties if the sched domain uses > > > asym_packing. (Ionela) > > > * Handle errors of arch_get_ipcc_score(). (Ionela) > > > > > > Changes since v1: > > > * Fixed a bug when selecting a busiest runqueue: when comparing two > > > runqueues with equal nr_running, we must compute the IPCC score delta > > > of both. > > > * Renamed local variables to improve the layout of the code block. > > > (PeterZ) > > > * Used the new interface names. > > > --- > > > kernel/sched/fair.c | 64 +++++++++++++++++++++++++++++++++++++++++++++ > > > 1 file changed, 64 insertions(+) > > > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > > index 72d88270b320..d3c22dc145f7 100644 > > > --- a/kernel/sched/fair.c > > > +++ b/kernel/sched/fair.c > > > @@ -9399,6 +9399,37 @@ static bool sched_asym_ipcc_pick(struct sched_group *a, > > > return sched_asym_ipcc_prefer(a_stats, b_stats); > > > } > > > > > > +/** > > > + * ipcc_score_delta - Get the IPCC score delta wrt the load balance's dst_cpu > > > + * @p: A task > > > + * @env: Load balancing environment > > > + * > > > + * Returns: The IPCC score delta that @p would get if placed in the destination > > > + * CPU of @env. LONG_MIN to indicate that the delta should not be used. > > > + */ > > > +static long ipcc_score_delta(struct task_struct *p, struct lb_env *env) > > > +{ > > > + unsigned long score_src, score_dst; > > > + unsigned short ipcc = p->ipcc; > > > + > > > + if (!sched_ipcc_enabled()) > > > + return LONG_MIN; > > > + > > > + /* Only asym_packing uses IPCC scores at the moment. */ > > > + if (!(env->sd->flags & SD_ASYM_PACKING)) > > > + return LONG_MIN; > > > + > > > + score_dst = arch_get_ipcc_score(ipcc, env->dst_cpu); > > > + if (IS_ERR_VALUE(score_dst)) > > > + return LONG_MIN; > > > + > > > + score_src = arch_get_ipcc_score(ipcc, task_cpu(p)); > > > + if (IS_ERR_VALUE(score_src)) > > > + return LONG_MIN; > > > + > > > + return score_dst - score_src; > > > +} > > > + > > > #else /* CONFIG_IPC_CLASSES */ > > > static void update_sg_lb_ipcc_stats(int dst_cpu, struct sg_lb_stats *sgs, > > > struct rq *rq) > > > @@ -9429,6 +9460,11 @@ static bool sched_asym_ipcc_pick(struct sched_group *a, > > > return false; > > > } > > > > > > +static long ipcc_score_delta(struct task_struct *p, struct lb_env *env) > > > +{ > > > + return LONG_MIN; > > > +} > > > + > > > #endif /* CONFIG_IPC_CLASSES */ > > > > > > /** > > > @@ -10589,6 +10625,7 @@ 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; > > > + long busiest_ipcc_delta = LONG_MIN; > > > unsigned int busiest_nr = 0; > > > int i; > > > > > > @@ -10705,8 +10742,35 @@ 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 IPCC 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); > > > > Hmm, i don't like this at all > > > > Also, curr is the least probable task to be pulled which means that > > all this his useless > > but when doing asym_packing balancing nr_running = 1, need_active_balance() > returns true and we will pull the current task, no? This is also true for > fully_busy groups with one task per CPU. These are the only two cases that > currently use IPCC scores.
hmm, for sure it's not true for fully_busy and I don't see anything about asym_packing mandating that nr_running = 1
You should have a look at misfit task which seems to better fit your situation where you have one task that doesn't fit its cpu instead of adding such condition > > If there are more than one tasks in the runqueue, the group will be > classified as overloaded and we will not use IPCC scores nor active > balance. > > Thanks and BR, > Ricardo
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