linux-kernel - [PATCH 2/3] sched/fair: don't set LBF_ALL

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Message-Id: <20210106133419.2971-3-vincent.guittot@linaro.org>
Date:   Wed,  6 Jan 2021 14:34:18 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, linux-kernel@...r.kernel.org
Cc:     Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH 2/3] sched/fair: don't set LBF_ALL_PINNED unnecessarily

Setting LBF_ALL_PINNED during active load balance is only valid when there
is only 1 running task on the rq otherwise this ends up increasing the
balance interval whereas other tasks could migrate after the next interval
once they become cache-cold as an example.

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/fair.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5428b8723e61..69a455113b10 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9759,7 +9759,8 @@ static int load_balance(int this_cpu, struct rq *this_rq,
 			if (!cpumask_test_cpu(this_cpu, busiest->curr->cpus_ptr)) {
 				raw_spin_unlock_irqrestore(&busiest->lock,
 							    flags);
-				env.flags |= LBF_ALL_PINNED;
+				if (busiest->nr_running == 1)
+					env.flags |= LBF_ALL_PINNED;
 				goto out_one_pinned;
 			}
 
-- 
2.17.1