linux-kernel - Re: [PATCH] sched/fair: add comments for group_type and balancing at SD

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Message-ID: <7325dac4-bb26-9fcb-75bc-15b68d35b62d@arm.com>
Date:   Tue, 12 Nov 2019 17:42:44 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        peterz@...radead.org, dietmar.eggemann@....com,
        juri.lelli@...hat.com, rostedt@...dmis.org, mgorman@...e.de
Cc:     bsegall@...gle.com
Subject: Re: [PATCH] sched/fair: add comments for group_type and balancing at
 SD_NUMA level

Hi Vincent,

On 12/11/2019 14:50, Vincent Guittot wrote:
> Add comments to describe each state of goup_type and to add some details
> about the load balance at NUMA level.
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>

Suggestions/nits below. There's a bit of duplication with existing
comments (e.g. the nice blob atop sg_imbalanced()), but I think it can't
hurt to have the few extra lines you're introducing.

---
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bfdcaf91b325..ec93ebd02352 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6955,28 +6955,26 @@ enum fbq_type { regular, remote, all };
  * group. see update_sd_pick_busiest().
  */
 enum group_type {
-	/*
-	 * The group has spare capacity that can be used to process more work.
-	 */
+	/* The group isn't significantly pressured and can be used to process more work */
 	group_has_spare = 0,
 	/*
 	 * The group is fully used and the tasks don't compete for more CPU
-	 * cycles. Nevetheless, some tasks might wait before running.
+	 * cycles. Nevertheless, some tasks might wait before running.
 	 */
 	group_fully_busy,
 	/*
-	 * One task doesn't fit with CPU's capacity and must be migrated on a
-	 * more powerful CPU.
+	 * (SD_ASYM_CPUCAPACITY only) One task doesn't fit on its CPU's
+	 * capacity and must be migrated to a CPU of higher capacity.
 	 */
 	group_misfit_task,
 	/*
-	 * One local CPU with higher capacity is available and task should be
-	 * migrated on it instead on current CPU.
+	 * (SD_ASYM_PACKING only) One local CPU with higher capacity is
+	 * available and task should be migrated to it.
 	 */
 	group_asym_packing,
 	/*
-	 * The tasks affinity prevents the scheduler to balance the load across
-	 * the system.
+	 * The tasks affinity previously prevented the scheduler from balancing
+	 * load across the system.
 	 */
 	group_imbalanced,
 	/*