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Message-ID: <Y5Gld+cThNOPFvgX@arm.com>
Date: Thu, 8 Dec 2022 08:51:03 +0000
From: Ionela Voinescu <ionela.voinescu@....com>
To: Ricardo Neri <ricardo.neri-calderon@...ux.intel.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>, 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>
Subject: Re: [PATCH v2 09/22] sched/fair: Use IPC class score to select a
busiest runqueue
Hi,
On Monday 28 Nov 2022 at 05:20:47 (-0800), Ricardo Neri 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.
>
[..]
> +static int ipcc_score_delta(struct task_struct *p, int alt_cpu)
> +{
> + unsigned long ipcc = p->ipcc;
> +
> + if (!sched_ipcc_enabled())
> + return INT_MIN;
> +
> + return arch_get_ipcc_score(ipcc, alt_cpu) -
> + arch_get_ipcc_score(ipcc, task_cpu(p));
Nit: arch_get_ipcc_score() return values are never checked for error.
> +}
> +
> #else /* CONFIG_IPC_CLASSES */
> static void update_sg_lb_ipcc_stats(struct sg_lb_ipcc_stats *sgcs,
> struct rq *rq)
> @@ -9258,6 +9276,11 @@ static bool sched_asym_ipcc_pick(struct sched_group *a,
> return false;
> }
>
> +static int ipcc_score_delta(struct task_struct *p, int alt_cpu)
> +{
> + return INT_MIN;
> +}
> +
> #endif /* CONFIG_IPC_CLASSES */
>
> /**
> @@ -10419,8 +10442,8 @@ 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;
> + int i, busiest_ipcc_delta = INT_MIN;
> unsigned int busiest_nr = 0;
> - int i;
>
> for_each_cpu_and(i, sched_group_span(group), env->cpus) {
> unsigned long capacity, load, util;
> @@ -10526,8 +10549,37 @@ 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 IPC 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->dst_cpu);
> + /*
> + * If rq and busiest have the same number of running
> + * tasks, pick rq if doing so would give rq::curr a
> + * bigger IPC boost on dst_cpu.
> + */
> + } else if (sched_ipcc_enabled() &&
> + busiest_nr == nr_running) {
> + struct task_struct *curr;
> + int delta;
> +
> + curr = rcu_dereference(rq->curr);
> + delta = ipcc_score_delta(curr, env->dst_cpu);
> +
> + if (busiest_ipcc_delta < delta) {
> + busiest_ipcc_delta = delta;
> + busiest_nr = nr_running;
> + busiest = rq;
> + }
> }
> break;
>
While in the commit message you describe this as breaking a tie for
asym_packing, the code here does not only affect asym_packing. If
another architecture would have sched_ipcc_enabled() it would use this
as generic policy, and that might not be desired.
Hope it helps,
Ionela.
> --
> 2.25.1
>
>
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