md/raid1: submit IO from originating thread instead of md thread.

queuing writes to the md thread means that all requests go through the
one processor which may not be able to keep up with very high request
rates.

So use the plugging infrastructure to submit all requests on unplug.
If a 'schedule' is needed, we fall back on the old approach of handing
the requests to the thread for it to handle.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 54 insertions, 3 deletions

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 36a8fc059ac..9f01870d031 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -870,6 +870,44 @@ do_sync_io:
 	pr_debug("%dB behind alloc failed, doing sync I/O\n", bio->bi_size);
 }
 
+struct raid1_plug_cb {
+	struct blk_plug_cb	cb;
+	struct bio_list		pending;
+	int			pending_cnt;
+};
+
+static void raid1_unplug(struct blk_plug_cb *cb, bool from_schedule)
+{
+	struct raid1_plug_cb *plug = container_of(cb, struct raid1_plug_cb,
+						  cb);
+	struct mddev *mddev = plug->cb.data;
+	struct r1conf *conf = mddev->private;
+	struct bio *bio;
+
+	if (from_schedule) {
+		spin_lock_irq(&conf->device_lock);
+		bio_list_merge(&conf->pending_bio_list, &plug->pending);
+		conf->pending_count += plug->pending_cnt;
+		spin_unlock_irq(&conf->device_lock);
+		md_wakeup_thread(mddev->thread);
+		kfree(plug);
+		return;
+	}
+
+	/* we aren't scheduling, so we can do the write-out directly. */
+	bio = bio_list_get(&plug->pending);
+	bitmap_unplug(mddev->bitmap);
+	wake_up(&conf->wait_barrier);
+
+	while (bio) { /* submit pending writes */
+		struct bio *next = bio->bi_next;
+		bio->bi_next = NULL;
+		generic_make_request(bio);
+		bio = next;
+	}
+	kfree(plug);
+}
+
 static void make_request(struct mddev *mddev, struct bio * bio)
 {
 	struct r1conf *conf = mddev->private;
@@ -883,6 +921,8 @@ static void make_request(struct mddev *mddev, struct bio * bio)
 	const unsigned long do_sync = (bio->bi_rw & REQ_SYNC);
 	const unsigned long do_flush_fua = (bio->bi_rw & (REQ_FLUSH | REQ_FUA));
 	struct md_rdev *blocked_rdev;
+	struct blk_plug_cb *cb;
+	struct raid1_plug_cb *plug = NULL;
 	int first_clone;
 	int sectors_handled;
 	int max_sectors;
@@ -1185,11 +1225,22 @@ read_again:
 		mbio->bi_private = r1_bio;
 
 		atomic_inc(&r1_bio->remaining);
+
+		cb = blk_check_plugged(raid1_unplug, mddev, sizeof(*plug));
+		if (cb)
+			plug = container_of(cb, struct raid1_plug_cb, cb);
+		else
+			plug = NULL;
 		spin_lock_irqsave(&conf->device_lock, flags);
-		bio_list_add(&conf->pending_bio_list, mbio);
-		conf->pending_count++;
+		if (plug) {
+			bio_list_add(&plug->pending, mbio);
+			plug->pending_cnt++;
+		} else {
+			bio_list_add(&conf->pending_bio_list, mbio);
+			conf->pending_count++;
+		}
 		spin_unlock_irqrestore(&conf->device_lock, flags);
-		if (!mddev_check_plugged(mddev))
+		if (!plug)
 			md_wakeup_thread(mddev->thread);
 	}
 	/* Mustn't call r1_bio_write_done before this next test,