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Commit ca5beb76 authored by Bart Van Assche's avatar Bart Van Assche Committed by Mike Snitzer
Browse files

dm mpath: micro-optimize the hot path relative to MPATHF_QUEUE_IF_NO_PATH 



Instead of checking MPATHF_QUEUE_IF_NO_PATH,
MPATHF_SAVED_QUEUE_IF_NO_PATH and the no_flush flag to decide whether
or not to push back a request (or bio) if there are no paths available,
only clear MPATHF_QUEUE_IF_NO_PATH in queue_if_no_path() if no_flush has
not been set.  The result is that only a single bit has to be tested in
the hot path to decide whether or not a request must be pushed back and
also that m->lock does not have to be taken in the hot path.

Signed-off-by: default avatarBart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: default avatarHannes Reinecke <hare@suse.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
parent 7e0d574f

drivers/md/dm-mpath.c

+11 −59
Original line number Diff line number Diff line
@@ -441,47 +441,6 @@ static struct pgpath *choose_pgpath(struct multipath *m, size_t nr_bytes) 
	return NULL;

}



/*

 * Check whether bios must be queued in the device-mapper core rather

 * than here in the target.

 *

 * If m->queue_if_no_path and m->saved_queue_if_no_path hold the

 * same value then we are not between multipath_presuspend()

 * and multipath_resume() calls and we have no need to check

 * for the DMF_NOFLUSH_SUSPENDING flag.

 */

static bool __must_push_back(struct multipath *m)

{

	return ((test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags) !=

		 test_bit(MPATHF_SAVED_QUEUE_IF_NO_PATH, &m->flags)) &&

		dm_noflush_suspending(m->ti));

}



static bool must_push_back_rq(struct multipath *m)

{

	bool r;

	unsigned long flags;



	spin_lock_irqsave(&m->lock, flags);

	r = (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags) ||

	     __must_push_back(m));

	spin_unlock_irqrestore(&m->lock, flags);



	return r;

}



static bool must_push_back_bio(struct multipath *m)

{

	bool r;

	unsigned long flags;



	spin_lock_irqsave(&m->lock, flags);

	r = __must_push_back(m);

	spin_unlock_irqrestore(&m->lock, flags);



	return r;

}



/*

 * Map cloned requests (request-based multipath)

 */
@@ -503,7 +462,7 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq, 
		pgpath = choose_pgpath(m, nr_bytes);



	if (!pgpath) {

		if (must_push_back_rq(m))

		if (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))

			return DM_MAPIO_DELAY_REQUEUE;

		return -EIO;	/* Failed */

	} else if (test_bit(MPATHF_QUEUE_IO, &m->flags) ||
@@ -580,9 +539,9 @@ static int __multipath_map_bio(struct multipath *m, struct bio *bio, struct dm_m 
	}



	if (!pgpath) {

		if (!must_push_back_bio(m))

			return -EIO;

		if (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))

			return DM_MAPIO_REQUEUE;

		return -EIO;

	}



	mpio->pgpath = pgpath;
@@ -674,7 +633,7 @@ static int queue_if_no_path(struct multipath *m, bool queue_if_no_path, 
		else

			clear_bit(MPATHF_SAVED_QUEUE_IF_NO_PATH, &m->flags);

	}

	if (queue_if_no_path)

	if (queue_if_no_path || dm_noflush_suspending(m->ti))

		set_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags);

	else

		clear_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags);
@@ -1519,12 +1478,9 @@ static int do_end_io(struct multipath *m, struct request *clone, 
	if (mpio->pgpath)

		fail_path(mpio->pgpath);



	if (!atomic_read(&m->nr_valid_paths)) {

		if (!test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) {

			if (!must_push_back_rq(m))

	if (atomic_read(&m->nr_valid_paths) == 0 &&

	    !test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))

		r = -EIO;

		}

	}



	return r;

}
@@ -1565,13 +1521,9 @@ static int do_end_io_bio(struct multipath *m, struct bio *clone, 
	if (mpio->pgpath)

		fail_path(mpio->pgpath);



	if (!atomic_read(&m->nr_valid_paths)) {

		if (!test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) {

			if (!must_push_back_bio(m))

	if (atomic_read(&m->nr_valid_paths) == 0 &&

	    !test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))

		return -EIO;

			return DM_ENDIO_REQUEUE;

		}

	}



	/* Queue for the daemon to resubmit */

	dm_bio_restore(get_bio_details_from_bio(clone), clone);