linux-kernel - [PATCH 4.14 128/211] sched/fair: Dont increase sd->balance

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Message-Id: <20191127203106.189140425@linuxfoundation.org>
Date:   Wed, 27 Nov 2019 21:31:01 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Valentin Schneider <valentin.schneider@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Dietmar.Eggemann@....com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>, patrick.bellasi@....com,
        vincent.guittot@...aro.org, Ingo Molnar <mingo@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.14 128/211] sched/fair: Dont increase sd->balance_interval on newidle balance

From: Valentin Schneider <valentin.schneider@....com>

[ Upstream commit 3f130a37c442d5c4d66531b240ebe9abfef426b5 ]

When load_balance() fails to move some load because of task affinity,
we end up increasing sd->balance_interval to delay the next periodic
balance in the hopes that next time we look, that annoying pinned
task(s) will be gone.

However, idle_balance() pays no attention to sd->balance_interval, yet
it will still lead to an increase in balance_interval in case of
pinned tasks.

If we're going through several newidle balances (e.g. we have a
periodic task), this can lead to a huge increase of the
balance_interval in a very small amount of time.

To prevent that, don't increase the balance interval when going
through a newidle balance.

This is a similar approach to what is done in commit 58b26c4c0257
("sched: Increment cache_nice_tries only on periodic lb"), where we
disregard newidle balance and rely on periodic balance for more stable
results.

Signed-off-by: Valentin Schneider <valentin.schneider@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Dietmar.Eggemann@....com
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: patrick.bellasi@....com
Cc: vincent.guittot@...aro.org
Link: http://lkml.kernel.org/r/1537974727-30788-2-git-send-email-valentin.schneider@arm.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Sasha Levin <sashal@...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 feeb52880d353..67433fbdcb5a4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8319,13 +8319,22 @@ static int load_balance(int this_cpu, struct rq *this_rq,
 	sd->nr_balance_failed = 0;
 
 out_one_pinned:
+	ld_moved = 0;
+
+	/*
+	 * idle_balance() disregards balance intervals, so we could repeatedly
+	 * reach this code, which would lead to balance_interval skyrocketting
+	 * in a short amount of time. Skip the balance_interval increase logic
+	 * to avoid that.
+	 */
+	if (env.idle == CPU_NEWLY_IDLE)
+		goto out;
+
 	/* tune up the balancing interval */
 	if (((env.flags & LBF_ALL_PINNED) &&
 			sd->balance_interval < MAX_PINNED_INTERVAL) ||
 			(sd->balance_interval < sd->max_interval))
 		sd->balance_interval *= 2;
-
-	ld_moved = 0;
 out:
 	return ld_moved;
 }
-- 
2.20.1