linux-kernel - [PATCH v4 2/4] sched/topology: Remove SD_BALANCE

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Message-Id: <20200206191957.12325-3-valentin.schneider@arm.com>
Date:   Thu,  6 Feb 2020 19:19:55 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...hat.com, peterz@...radead.org, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, morten.rasmussen@....com,
        qperret@...gle.com, adharmap@...eaurora.org,
        pkondeti@...eaurora.org
Subject: [PATCH v4 2/4] sched/topology: Remove SD_BALANCE_WAKE on asymmetric capacity systems

From: Morten Rasmussen <morten.rasmussen@....com>

SD_BALANCE_WAKE was previously added to lower sched_domain levels on
asymmetric CPU capacity systems by commit 9ee1cda5ee25 ("sched/core: Enable
SD_BALANCE_WAKE for asymmetric capacity systems") to enable the use of
find_idlest_cpu() and friends to find an appropriate CPU for tasks.

That responsibility has now been shifted to select_idle_sibling() and
friends, and hence the flag can be removed. Note that this causes
asymmetric CPU capacity systems to no longer enter the slow wakeup path
(find_idlest_cpu()) on wakeups - only on execs and forks (which is aligned
with all other mainline topologies).

Signed-off-by: Morten Rasmussen <morten.rasmussen@....com>
[Changelog tweaks]
Signed-off-by: Valentin Schneider <valentin.schneider@....com>
---
 kernel/sched/topology.c | 15 +++------------
 1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index dfb64c08a407a..00911884b7e7a 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1374,18 +1374,9 @@ sd_init(struct sched_domain_topology_level *tl,
 	 * Convert topological properties into behaviour.
 	 */
 
-	if (sd->flags & SD_ASYM_CPUCAPACITY) {
-		struct sched_domain *t = sd;
-
-		/*
-		 * Don't attempt to spread across CPUs of different capacities.
-		 */
-		if (sd->child)
-			sd->child->flags &= ~SD_PREFER_SIBLING;
-
-		for_each_lower_domain(t)
-			t->flags |= SD_BALANCE_WAKE;
-	}
+	/* Don't attempt to spread across CPUs of different capacities. */
+	if ((sd->flags & SD_ASYM_CPUCAPACITY) && sd->child)
+		sd->child->flags &= ~SD_PREFER_SIBLING;
 
 	if (sd->flags & SD_SHARE_CPUCAPACITY) {
 		sd->imbalance_pct = 110;
-- 
2.24.0