linux-kernel - [PATCH v3 07/10] sched/fair: Do not even the number of busy CPUs via asym

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Date:   Mon,  6 Feb 2023 20:58:35 -0800
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>,
        Ionela Voinescu <ionela.voinescu@....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 v3 07/10] sched/fair: Do not even the number of busy CPUs via asym_packing

Now that find_busiest_group() triggers load balancing between a fully_
busy SMT2 core and an idle non-SMT core, it is no longer needed to force
balancing via asym_packing. Use asym_packing only as intended: when there
is high-priority CPU that is idle.

After this change, the same logic apply to SMT and non-SMT local groups.
Simplify asym_smt_can_pull_tasks() accordingly.

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
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
---
Changes since v2:
 * Introduced this patch.

Changes since v1:
 * N/A
---
 kernel/sched/fair.c | 37 +++++--------------------------------
 1 file changed, 5 insertions(+), 32 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a37ad59f20ea..0ada2d18b934 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9247,20 +9247,15 @@ group_type group_classify(unsigned int imbalance_pct,
  * @sgs:	Load-balancing statistics of the candidate busiest group
  * @sg:		The candidate busiest group
  *
- * Check the state of the SMT siblings of both @sds::local and @sg and decide
- * if @dst_cpu can pull tasks.
+ * Check the state of the SMT siblings of @sg and decide if @dst_cpu can pull
+ * tasks.
  *
  * This function must be called only if all the SMT siblings of @dst_cpu are
  * idle, if any.
  *
- * If @dst_cpu does not have SMT siblings, it can pull tasks if two or more of
- * the SMT siblings of @sg are busy. If only one CPU in @sg is busy, pull tasks
- * only if @dst_cpu has higher priority.
- *
- * If @dst_cpu has SMT siblings, decide based on the priority of @sg. Do it only
- * if @sg has exactly one busy CPU (i.e., one more than @sds::local). Bigger
- * imbalances in the number of busy CPUs will be dealt with in
- * find_busiest_group().
+ * @dst_cpu can pull tasks if @sg has exactly one busy CPU (i.e., one more than
+ * @sds::local) and has lower group priority than @sds::local. Bigger imbalances
+ * in the number of busy CPUs will be dealt with in find_busiest_group().
  *
  * Return: true if @dst_cpu can pull tasks, false otherwise.
  */
@@ -9269,33 +9264,11 @@ static bool asym_smt_can_pull_tasks(int dst_cpu, struct sd_lb_stats *sds,
 				    struct sched_group *sg)
 {
 #ifdef CONFIG_SCHED_SMT
-	bool local_is_smt;
 	int sg_busy_cpus;
 
-	local_is_smt = sds->local->flags & SD_SHARE_CPUCAPACITY;
 	sg_busy_cpus = sgs->group_weight - sgs->idle_cpus;
 
-	if (!local_is_smt) {
-		/*
-		 * If we are here, @dst_cpu is idle and does not have SMT
-		 * siblings. Pull tasks if candidate group has two or more
-		 * busy CPUs.
-		 */
-		if (sg_busy_cpus >= 2) /* implies sg_is_smt */
-			return true;
-
-		/*
-		 * @dst_cpu does not have SMT siblings. @sg may have SMT
-		 * siblings and only one is busy. In such case, @dst_cpu
-		 * can help if it has higher priority and is idle (i.e.,
-		 * it has no running tasks).
-		 */
-		return sched_asym_prefer(dst_cpu, sg->asym_prefer_cpu);
-	}
-
 	/*
-	 * @dst_cpu has SMT siblings and are also idle.
-	 *
 	 * If the difference in the number of busy CPUs is two or more, let
 	 * find_busiest_group() take care of it. We only care if @sg has
 	 * exactly one busy CPU. This covers SMT and non-SMT sched groups.
-- 
2.25.1