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    Subject[PATCH 4.19 202/306] sched/fair: Dont increase sd->balance_interval on newidle balance
    Date
    From: Valentin Schneider <valentin.schneider@arm.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@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>
    ---
    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 e5e8f67218728..f77fcd37b226f 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -8819,13 +8819,22 @@ 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


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