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SubjectRe: [PATCH v3 3/5] md/raid10: prevent unnecessary calls to wake_up() in fast path
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On 9/16/22 7:34 PM, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
>
> Currently, wake_up() is called unconditionally in fast path such as
> raid10_make_request(), which will cause lock contention under high
> concurrency:
>
> raid10_make_request
> wake_up
> __wake_up_common_lock
> spin_lock_irqsave
>
> Improve performance by only call wake_up() if waitqueue is not empty
> in allow_barrier() and raid10_make_request().
>
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
> drivers/md/raid10.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index df435d693637..cf452c25e1e5 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -274,6 +274,12 @@ static void put_buf(struct r10bio *r10_bio)
> lower_barrier(conf);
> }
>
> +static void wake_up_barrier(struct r10conf *conf)
> +{
> + if (wq_has_sleeper(&conf->wait_barrier))
> + wake_up(&conf->wait_barrier);
> +}
> +
> static void reschedule_retry(struct r10bio *r10_bio)
> {
> unsigned long flags;
> @@ -1015,7 +1021,7 @@ static void allow_barrier(struct r10conf *conf)
> {
> if ((atomic_dec_and_test(&conf->nr_pending)) ||
> (conf->array_freeze_pending))
> - wake_up(&conf->wait_barrier);
> + wake_up_barrier(conf);
> }
>
> static void freeze_array(struct r10conf *conf, int extra)
> @@ -1891,7 +1897,7 @@ static bool raid10_make_request(struct mddev *mddev, struct bio *bio)
> __make_request(mddev, bio, sectors);
>
> /* In case raid10d snuck in to freeze_array */
> - wake_up(&conf->wait_barrier);
> + wake_up_barrier(conf);
> return true;
> }
>

Acked-by: Guoqing Jiang <guoqing.jiang@linux.dev>

Thanks,
Guoqing

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