Messages in this thread | | | From | Vincent Guittot <> | Date | Tue, 28 Mar 2023 12:03:58 +0200 | Subject | Re: [PATCH v3 10/24] sched/fair: Use IPCC scores to select a busiest runqueue |
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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 > > 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
> + /* > + * If rq and busiest have the same number of running > + * tasks and IPC classes are supported, pick rq if doing > + * so would give rq::curr a bigger IPC boost on dst_cpu. > + */ > + } else if (busiest_nr == nr_running) { > + struct task_struct *curr; > + long delta; > + > + curr = rcu_dereference(rq->curr); > + delta = ipcc_score_delta(curr, env); > + > + if (busiest_ipcc_delta < delta) { > + busiest_ipcc_delta = delta; > + busiest_nr = nr_running; > + busiest = rq; > + } > } > break; > > -- > 2.25.1 >
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