linux-kernel - [PATCH 3/4] sched/fair: Let lower-priority CPUs do active balancing

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Message-Id: <20220825225529.26465-4-ricardo.neri-calderon@linux.intel.com>
Date:   Thu, 25 Aug 2022 15:55:28 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Cc:     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,
        linux-kernel@...r.kernel.org,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        "Tim C . Chen" <tim.c.chen@...el.com>
Subject: [PATCH 3/4] sched/fair: Let lower-priority CPUs do active balancing

When more than one SMT siblings of a physical core are busy, an idle CPU
of lower priority can help.

Indicate that the low priority CPU can do active balancing from the high-
priority CPU only if they belong to separate cores.

Cc: Ben Segall <bsegall@...gle.com>
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Len Brown <len.brown@...el.com>
Cc: Mel Gorman <mgorman@...e.de>
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: x86@...nel.org
Cc: linux-kernel@...r.kernel.org
Reviewed-by: Len Brown <len.brown@...el.com>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
---
 kernel/sched/fair.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 810645eb58ed..9b608b31080f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9759,9 +9759,14 @@ asym_active_balance(struct lb_env *env)
 	 * ASYM_PACKING needs to force migrate tasks from busy but
 	 * lower priority CPUs in order to pack all tasks in the
 	 * highest priority CPUs.
+	 *
+	 * If the busy CPU has higher priority but is an SMT sibling
+	 * in which other SMT siblings are also busy, a lower-priority
+	 * CPU in a separate core can help.
 	 */
 	return env->idle != CPU_NOT_IDLE && (env->sd->flags & SD_ASYM_PACKING) &&
-	       sched_asym_prefer(env->dst_cpu, env->src_cpu);
+	       (sched_asym_prefer(env->dst_cpu, env->src_cpu) ||
+		!(env->sd->flags & SD_SHARE_CPUCAPACITY));
 }
 
 static inline bool
-- 
2.25.1