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Message-ID: <20230624002505.GB32639@ranerica-svr.sc.intel.com>
Date: Fri, 23 Jun 2023 17:25:05 -0700
From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To: Ionela Voinescu <ionela.voinescu@....com>
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Ricardo Neri <ricardo.neri@...el.com>,
"Ravi V. Shankar" <ravi.v.shankar@...el.com>,
Ben Segall <bsegall@...gle.com>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Len Brown <len.brown@...el.com>, Mel Gorman <mgorman@...e.de>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
Steven Rostedt <rostedt@...dmis.org>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Valentin Schneider <vschneid@...hat.com>,
Lukasz Luba <lukasz.luba@....com>,
Zhao Liu <zhao1.liu@...el.com>,
"Yuan, Perry" <Perry.Yuan@....com>, x86@...nel.org,
"Joel Fernandes (Google)" <joel@...lfernandes.org>,
linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
"Tim C . Chen" <tim.c.chen@...el.com>,
Zhao Liu <zhao1.liu@...ux.intel.com>
Subject: Re: [PATCH v4 10/24] sched/fair: Use IPCC scores to select a busiest
runqueue
On Thu, Jun 22, 2023 at 10:03:17AM +0100, Ionela Voinescu wrote:
> 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@...gle.com>
> > Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
> > Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> > Cc: Ionela Voinescu <ionela.voinescu@....com>
> > Cc: Joel Fernandes (Google) <joel@...lfernandes.org>
> > Cc: Len Brown <len.brown@...el.com>
> > Cc: Lukasz Luba <lukasz.luba@....com>
> > Cc: Mel Gorman <mgorman@...e.de>
> > Cc: Perry Yuan <Perry.Yuan@....com>
> > Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Tim C. Chen <tim.c.chen@...el.com>
> > Cc: Valentin Schneider <vschneid@...hat.com>
> > Cc: Zhao Liu <zhao1.liu@...ux.intel.com>
> > Cc: x86@...nel.org
> > Cc: linux-pm@...r.kernel.org
> > Cc: linux-kernel@...r.kernel.org
> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.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.
True! I will remove this pointless assignment.
Thanks and BR,
Ricardo
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