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Subject[PATCH -next 3/3] md/raid10: prevent unnecessary calls to wake_up() in fast path
Date
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.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
drivers/md/raid10.c | 26 ++++++++++++++++----------
1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 086216b051f5..2f7c8bef6dc2 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;
@@ -286,7 +292,7 @@ static void reschedule_retry(struct r10bio *r10_bio)
spin_unlock_irqrestore(&conf->device_lock, flags);

/* wake up frozen array... */
- wake_up(&conf->wait_barrier);
+ wake_up_barrier(conf);

md_wakeup_thread(mddev->thread);
}
@@ -884,7 +890,7 @@ static void flush_pending_writes(struct r10conf *conf)
/* flush any pending bitmap writes to disk
* before proceeding w/ I/O */
md_bitmap_unplug(conf->mddev->bitmap);
- wake_up(&conf->wait_barrier);
+ wake_up_barrier(conf);

while (bio) { /* submit pending writes */
struct bio *next = bio->bi_next;
@@ -955,7 +961,7 @@ static void lower_barrier(struct r10conf *conf)
write_seqlock_irqsave(&conf->resync_lock, flags);
WRITE_ONCE(conf->barrier, conf->barrier - 1);
write_sequnlock_irqrestore(&conf->resync_lock, flags);
- wake_up(&conf->wait_barrier);
+ wake_up_barrier(conf);
}

static bool wait_barrier_nolock(struct r10conf *conf)
@@ -1018,7 +1024,7 @@ static bool wait_barrier(struct r10conf *conf, bool nowait)
}
conf->nr_waiting--;
if (!conf->nr_waiting)
- wake_up(&conf->wait_barrier);
+ wake_up_barrier(conf);
}
/* Only increment nr_pending when we wait */
if (ret)
@@ -1031,7 +1037,7 @@ 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)
@@ -1067,7 +1073,7 @@ static void unfreeze_array(struct r10conf *conf)
write_seqlock_irq(&conf->resync_lock);
WRITE_ONCE(conf->barrier, conf->barrier - 1);
conf->nr_waiting--;
- wake_up(&conf->wait_barrier);
+ wake_up_barrier(conf);
write_sequnlock_irq(&conf->resync_lock);
}

@@ -1092,7 +1098,7 @@ static void raid10_unplug(struct blk_plug_cb *cb, bool from_schedule)
spin_lock_irq(&conf->device_lock);
bio_list_merge(&conf->pending_bio_list, &plug->pending);
spin_unlock_irq(&conf->device_lock);
- wake_up(&conf->wait_barrier);
+ wake_up_barrier(conf);
md_wakeup_thread(mddev->thread);
kfree(plug);
return;
@@ -1101,7 +1107,7 @@ static void raid10_unplug(struct blk_plug_cb *cb, bool from_schedule)
/* we aren't scheduling, so we can do the write-out directly. */
bio = bio_list_get(&plug->pending);
md_bitmap_unplug(mddev->bitmap);
- wake_up(&conf->wait_barrier);
+ wake_up_barrier(conf);

while (bio) { /* submit pending writes */
struct bio *next = bio->bi_next;
@@ -1907,7 +1913,7 @@ 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;
}

@@ -3055,7 +3061,7 @@ static void handle_write_completed(struct r10conf *conf, struct r10bio *r10_bio)
* In case freeze_array() is waiting for condition
* nr_pending == nr_queued + extra to be true.
*/
- wake_up(&conf->wait_barrier);
+ wake_up_barrier(conf);
md_wakeup_thread(conf->mddev->thread);
} else {
if (test_bit(R10BIO_WriteError,
--
2.31.1
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