sched/fair: Don't increase sd->balance_interval on newidle balance

BugLink: https://bugs.launchpad.net/bugs/1854975
[ 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@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Dietmar.Eggemann@arm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: patrick.bellasi@arm.com
Cc: vincent.guittot@linaro.org
Link: http://lkml.kernel.org/r/1537974727-30788-2-git-send-email-valentin.schneider@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6c5766f9e9240789002f2a740b4a96fbcffd2b90..5a50a874772a50958fc79ac5a937f347d1671d67 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8709,13 +8709,22 @@ out_all_pinned:
        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;
 }