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Commit 27c0f68f authored by Shaohua Li's avatar Shaohua Li Committed by NeilBrown
Browse files

raid5: make_request does less prepare wait 



In NUMA machine, prepare_to_wait/finish_wait in make_request exposes a
lot of contention for sequential workload (or big request size
workload). For such workload, each bio includes several stripes. So we
can just do prepare_to_wait/finish_wait once for the whold bio instead
of every stripe.  This reduces the lock contention completely for such
workload. Random workload might have the similar lock contention too,
but I didn't see it yet, maybe because my stroage is still not fast
enough.

Signed-off-by: default avatarShaohua Li <shli@fusionio.com>
Signed-off-by: default avatarNeilBrown <neilb@suse.de>
parent e2f23b60

drivers/md/raid5.c

+14 −5
Original line number Diff line number Diff line
@@ -4552,6 +4552,8 @@ static void make_request(struct mddev *mddev, struct bio * bi) 
	struct stripe_head *sh;

	const int rw = bio_data_dir(bi);

	int remaining;

	DEFINE_WAIT(w);

	bool do_prepare;



	if (unlikely(bi->bi_rw & REQ_FLUSH)) {

		md_flush_request(mddev, bi);
@@ -4575,15 +4577,18 @@ static void make_request(struct mddev *mddev, struct bio * bi) 
	bi->bi_next = NULL;

	bi->bi_phys_segments = 1;	/* over-loaded to count active stripes */



	prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);

	for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {

		DEFINE_WAIT(w);

		int previous;

		int seq;



		do_prepare = false;

	retry:

		seq = read_seqcount_begin(&conf->gen_lock);

		previous = 0;

		prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);

		if (do_prepare)

			prepare_to_wait(&conf->wait_for_overlap, &w,

				TASK_UNINTERRUPTIBLE);

		if (unlikely(conf->reshape_progress != MaxSector)) {

			/* spinlock is needed as reshape_progress may be

			 * 64bit on a 32bit platform, and so it might be
@@ -4604,6 +4609,7 @@ static void make_request(struct mddev *mddev, struct bio * bi) 
				    : logical_sector >= conf->reshape_safe) {

					spin_unlock_irq(&conf->device_lock);

					schedule();

					do_prepare = true;

					goto retry;

				}

			}
@@ -4640,6 +4646,7 @@ static void make_request(struct mddev *mddev, struct bio * bi) 
				if (must_retry) {

					release_stripe(sh);

					schedule();

					do_prepare = true;

					goto retry;

				}

			}
@@ -4663,8 +4670,10 @@ static void make_request(struct mddev *mddev, struct bio * bi) 
				prepare_to_wait(&conf->wait_for_overlap,

						&w, TASK_INTERRUPTIBLE);

				if (logical_sector >= mddev->suspend_lo &&

				    logical_sector < mddev->suspend_hi)

				    logical_sector < mddev->suspend_hi) {

					schedule();

					do_prepare = true;

				}

				goto retry;

			}
@@ -4677,9 +4686,9 @@ static void make_request(struct mddev *mddev, struct bio * bi) 
				md_wakeup_thread(mddev->thread);

				release_stripe(sh);

				schedule();

				do_prepare = true;

				goto retry;

			}

			finish_wait(&conf->wait_for_overlap, &w);

			set_bit(STRIPE_HANDLE, &sh->state);

			clear_bit(STRIPE_DELAYED, &sh->state);

			if ((bi->bi_rw & REQ_SYNC) &&
@@ -4689,10 +4698,10 @@ static void make_request(struct mddev *mddev, struct bio * bi) 
		} else {

			/* cannot get stripe for read-ahead, just give-up */

			clear_bit(BIO_UPTODATE, &bi->bi_flags);

			finish_wait(&conf->wait_for_overlap, &w);

			break;

		}

	}

	finish_wait(&conf->wait_for_overlap, &w);



	remaining = raid5_dec_bi_active_stripes(bi);

	if (remaining == 0) {