linux-kernel - [tip:sched/urgent] sched/fair: Comment some nohz_balancer

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Message-ID: <tip-66856ff8e727e7da7da44a634f314b236510f419@git.kernel.org>
Date:   Sat, 9 Mar 2019 06:36:47 -0800
From:   tip-bot for Valentin Schneider <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     mingo@...nel.org, peterz@...radead.org, tglx@...utronix.de,
        valentin.schneider@....com, luto@...nel.org,
        dave.hansen@...ux.intel.com, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, hpa@...or.com, bp@...en8.de,
        riel@...riel.com
Subject: [tip:sched/urgent] sched/fair: Comment some nohz_balancer_kick()
 kick conditions

Commit-ID:  66856ff8e727e7da7da44a634f314b236510f419
Gitweb:     https://git.kernel.org/tip/66856ff8e727e7da7da44a634f314b236510f419
Author:     Valentin Schneider <valentin.schneider@....com>
AuthorDate: Mon, 11 Feb 2019 17:59:44 +0000
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Sat, 9 Mar 2019 14:03:52 +0100

sched/fair: Comment some nohz_balancer_kick() kick conditions

We now have a comment explaining the first sched_domain based NOHZ kick,
so might as well comment them all.

While at it, unwrap a line that fits under 80 characters.

Co-authored-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Valentin Schneider <valentin.schneider@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Dietmar.Eggemann@....com
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...riel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: morten.rasmussen@....com
Cc: vincent.guittot@...aro.org
Link: https://lkml.kernel.org/r/20190211175946.4961-2-valentin.schneider@arm.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/fair.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8213ff6e365d..e6f7d39d4d45 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9612,8 +9612,12 @@ static void nohz_balancer_kick(struct rq *rq)
 
 	sd = rcu_dereference(rq->sd);
 	if (sd) {
-		if ((rq->cfs.h_nr_running >= 1) &&
-		    check_cpu_capacity(rq, sd)) {
+		/*
+		 * If there's a CFS task and the current CPU has reduced
+		 * capacity; kick the ILB to see if there's a better CPU to run
+		 * on.
+		 */
+		if (rq->cfs.h_nr_running >= 1 && check_cpu_capacity(rq, sd)) {
 			flags = NOHZ_KICK_MASK;
 			goto unlock;
 		}
@@ -9621,6 +9625,11 @@ static void nohz_balancer_kick(struct rq *rq)
 
 	sd = rcu_dereference(per_cpu(sd_asym_packing, cpu));
 	if (sd) {
+		/*
+		 * When ASYM_PACKING; see if there's a more preferred CPU
+		 * currently idle; in which case, kick the ILB to move tasks
+		 * around.
+		 */
 		for_each_cpu_and(i, sched_domain_span(sd), nohz.idle_cpus_mask) {
 			if (sched_asym_prefer(i, cpu)) {
 				flags = NOHZ_KICK_MASK;