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Date: Fri, 05 May 2023 15:29:45 -0700
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: 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>,
Valentin Schneider <vschneid@...hat.com>,
Ionela Voinescu <ionela.voinescu@....com>, x86@...nel.org,
linux-kernel@...r.kernel.org,
Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
naveen.n.rao@...ux.vnet.ibm.com,
Yicong Yang <yangyicong@...ilicon.com>,
Barry Song <v-songbaohua@...o.com>,
Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Subject: Re: [PATCH 2/6] sched/fair: Check whether active load balance is
needed in busiest group
On Fri, 2023-05-05 at 14:16 +0200, Peter Zijlstra wrote:
>
> > +static inline bool asym_active_balance_busiest(struct lb_env *env, struct sd_lb_stats *sds)
> > +{
> > + /*
> > + * Don't balance to a group without spare capacity.
> > + *
> > + * Skip non asymmetric sched group balancing. That check
> > + * is handled by code path handling imbalanced load between
> > + * similar groups.
> > + */
> > + if (env->idle == CPU_NOT_IDLE ||
> > + sds->local_stat.group_type != group_has_spare ||
> > + !asymmetric_groups(sds->local, sds->busiest))
> > + return false;
> > +
> > + /*
> > + * For SMT source group, pull when there are two or more
> > + * tasks over-utilizing a core.
> > + */
> > + if (sds->busiest->flags & SD_SHARE_CPUCAPACITY &&
> > + sds->busiest_stat.sum_h_nr_running > 1)
> > + return true;
> > +
> > + return false;
> > +}
>
> This all seems to be mixing two 'asymmetric' things in the 'asym'
> namespace :/ One being the SD_ASYM_PACKING and then the above SMT/no-SMT
> core thing.
Yeah, I am kind of abusing the "asymmetric" word. However, the above
code does try to set things up for the aysm_active_balance() code
later. Any suggestion on better names for "asymmetric_groups()" and
and "asym_active_balance_busiest()"?
Perhaps "hybrid_groups()" and "hybrid_active_balance_busiest()"?
>
> > +
> > /**
> > * calculate_imbalance - Calculate the amount of imbalance present within the
> > * groups of a given sched_domain during load balance.
> > @@ -10164,6 +10200,12 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
> > return;
> > }
> >
> > + if (asym_active_balance_busiest(env, sds)) {
> > + env->migration_type = migrate_task;
> > + env->imbalance = 1;
> > + return;
> > + }
> > +
> > if (busiest->group_weight == 1 || sds->prefer_sibling) {
> > unsigned int nr_diff = busiest->sum_nr_running;
> > /*
> > @@ -10371,6 +10413,9 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
> > */
> > goto out_balanced;
> >
> > + if (asym_active_balance_busiest(env, &sds))
> > + goto force_balance;
> > +
> > if (busiest->group_weight > 1 &&
> > local->idle_cpus <= (busiest->idle_cpus + 1))
> > /*
>
> All the cases here have a nice (CodingStyle busting) comment, perhaps
> add the missing {} when hou add the comment?
Sure, will add a comment here.
Tim
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