Messages in this thread | | | Date | Thu, 22 Jun 2023 10:03:17 +0100 | From | Ionela Voinescu <> | Subject | Re: [PATCH v4 10/24] sched/fair: Use IPCC scores to select a busiest runqueue |
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On Monday 12 Jun 2023 at 21:24:08 (-0700), Ricardo Neri wrote: > Use IPCC scores to break a tie between two runqueues with the same priority > and number of running tasks: select the runqueue of which the task enqueued > last would get a higher IPC boost when migrated to the destination CPU. > (These tasks are migrated first during load balance.) > > For now, restrict the utilization of IPCC scores to scheduling domains > marked 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: Perry Yuan <Perry.Yuan@amd.com> > 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: Zhao Liu <zhao1.liu@linux.intel.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 v3: > * Do not compute the IPCC stats using the current tasks of runqueues. > Instead, use the tasks at the back of the queue. These are the tasks > that will be pulled first during load balance. (Vincent) > > 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 | 61 +++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 61 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index fcec791ede4f..da3e009eef42 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -9564,6 +9564,41 @@ 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 > + * @rq: A runqueue > + * @env: Load balancing environment > + * > + * Returns: The IPCC score delta that the last task enqueued in @rq 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 rq *rq, struct lb_env *env) > +{ > + unsigned long score_src, score_dst; > + unsigned short 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; > + > + if (rq_last_task_ipcc(env->dst_cpu, rq, &ipcc)) > + 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, cpu_of(rq)); > + 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) > @@ -9594,6 +9629,11 @@ static bool sched_asym_ipcc_pick(struct sched_group *a, > return false; > } > > +static long ipcc_score_delta(struct rq *rq, struct lb_env *env) > +{ > + return LONG_MIN; > +} > + > #endif /* CONFIG_IPC_CLASSES */ > > /** > @@ -10769,6 +10809,7 @@ 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; > > @@ -10885,6 +10926,26 @@ static struct rq *find_busiest_queue(struct lb_env *env, > if (busiest_nr < nr_running) { > busiest_nr = nr_running; > busiest = rq; > + > + /* > + * Remember the IPCC score of the busiest > + * runqueue. We may need it to break a tie with > + * other queues with equal nr_running. > + */ > + busiest_ipcc_delta = ipcc_score_delta(busiest, env); > + /* > + * For ties, select @rq if doing would give its last > + * queued task a bigger IPC boost when migrated to > + * dst_cpu. > + */ > + } else if (busiest_nr == nr_running) { > + long delta = ipcc_score_delta(rq, env); > + > + if (busiest_ipcc_delta < delta) { > + busiest_ipcc_delta = delta; > + busiest_nr = nr_running;
nit: there's no need as busiest_nr is already equal to nr_running.
Ionela.
> + busiest = rq; > + } > } > break; > > -- > 2.25.1 >
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