From c0662fa63a10ff5a0ebe72c9a213aa0b6d4826f0 Mon Sep 17 00:00:00 2001
From: Valentin Schneider <valentin.schneider@arm.com>
Date: Mon, 14 Oct 2019 17:44:08 +0100
Subject: [PATCH] sched/topology: Don't set SD_BALANCE_WAKE on cpuset domain
 relax

References: bnc#1155798 (CPU scheduler functional and performance backports)
Patch-mainline: v5.5-rc1
Git-commit: 9ae7ab20b4835dbea0e5fc6a5c70171dc354a72e

As pointed out in commit

  182a85f8a119 ("sched: Disable wakeup balancing")

SD_BALANCE_WAKE is a tad too aggressive, and is usually left unset.

However, it turns out cpuset domain relaxation will unconditionally set it
on domains below the relaxation level. This made sense back when
SD_BALANCE_WAKE was set unconditionally, but it no longer is the case.

We can improve things slightly by noticing that set_domain_attribute() is
always called after sd_init(), so rather than setting flags we can rely on
whatever sd_init() is doing and only clear certain flags when above the
relaxation level.

While at it, slightly clean up the function and flip the relax level
check to be more human readable.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: mingo@kernel.org
Cc: vincent.guittot@linaro.org
Cc: juri.lelli@redhat.com
Cc: seto.hidetoshi@jp.fujitsu.com
Cc: qperret@google.com
Cc: Dietmar.Eggemann@arm.com
Cc: morten.rasmussen@arm.com
Link: https://lkml.kernel.org/r/20191014164408.32596-1-valentin.schneider@arm.com
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 kernel/sched/topology.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 49b835f1305f..6ec1e595b1d4 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1201,16 +1201,13 @@ static void set_domain_attribute(struct sched_domain *sd,
 	if (!attr || attr->relax_domain_level < 0) {
 		if (default_relax_domain_level < 0)
 			return;
-		else
-			request = default_relax_domain_level;
+		request = default_relax_domain_level;
 	} else
 		request = attr->relax_domain_level;
-	if (request < sd->level) {
+
+	if (sd->level > request) {
 		/* Turn off idle balance on this domain: */
 		sd->flags &= ~(SD_BALANCE_WAKE|SD_BALANCE_NEWIDLE);
-	} else {
-		/* Turn on idle balance on this domain: */
-		sd->flags |= (SD_BALANCE_WAKE|SD_BALANCE_NEWIDLE);
 	}
 }