Commit e8299874 authored by Lars Ellenberg's avatar Lars Ellenberg Committed by Jens Axboe
Browse files

drbd: don't let application IO pre-empt resync too often 



Before, application IO could pre-empt resync activity
for up to hardcoded 20 seconds per resync request.
A very busy server could throttle the effective resync bandwidth
down to one request per 20 seconds.

Now, we only let application IO pre-empt resync traffic
while the current resync rate estimate is above c-min-rate.

If you disable the c-min-rate throttle feature (set c-min-rate = 0),
application IO will no longer pre-empt resync traffic at all.

Signed-off-by: default avatarPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: default avatarLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent 0e49d7b0

drivers/block/drbd/drbd_actlog.c

+6 −7
Original line number Diff line number Diff line
@@ -1022,8 +1022,7 @@ int drbd_rs_begin_io(struct drbd_device *device, sector_t sector) 
	unsigned int enr = BM_SECT_TO_EXT(sector);

	struct bm_extent *bm_ext;

	int i, sig;

	int sa = 200; /* Step aside 200 times, then grab the extent and let app-IO wait.

			 200 times -> 20 seconds. */

	bool sa;



retry:

	sig = wait_event_interruptible(device->al_wait,
@@ -1034,12 +1033,15 @@ retry: 
	if (test_bit(BME_LOCKED, &bm_ext->flags))

		return 0;



	/* step aside only while we are above c-min-rate; unless disabled. */

	sa = drbd_rs_c_min_rate_throttle(device);



	for (i = 0; i < AL_EXT_PER_BM_SECT; i++) {

		sig = wait_event_interruptible(device->al_wait,

					       !_is_in_al(device, enr * AL_EXT_PER_BM_SECT + i) ||

					       test_bit(BME_PRIORITY, &bm_ext->flags));

					       (sa && test_bit(BME_PRIORITY, &bm_ext->flags)));



		if (sig || (test_bit(BME_PRIORITY, &bm_ext->flags) && sa)) {

		if (sig || (sa && test_bit(BME_PRIORITY, &bm_ext->flags))) {

			spin_lock_irq(&device->al_lock);

			if (lc_put(device->resync, &bm_ext->lce) == 0) {

				bm_ext->flags = 0; /* clears BME_NO_WRITES and eventually BME_PRIORITY */
@@ -1051,9 +1053,6 @@ retry: 
				return -EINTR;

			if (schedule_timeout_interruptible(HZ/10))

				return -EINTR;

			if (sa && --sa == 0)

				drbd_warn(device, "drbd_rs_begin_io() stepped aside for 20sec."

					 "Resync stalled?\n");

			goto retry;

		}

	}

drivers/block/drbd/drbd_int.h

+2 −1
Original line number Diff line number Diff line
@@ -1339,7 +1339,8 @@ extern void start_resync_timer_fn(unsigned long data); 
/* drbd_receiver.c */

extern int drbd_receiver(struct drbd_thread *thi);

extern int drbd_asender(struct drbd_thread *thi);

extern int drbd_rs_should_slow_down(struct drbd_device *device, sector_t sector);

extern bool drbd_rs_c_min_rate_throttle(struct drbd_device *device);

extern bool drbd_rs_should_slow_down(struct drbd_device *device, sector_t sector);

extern int drbd_submit_peer_request(struct drbd_device *,

				    struct drbd_peer_request *, const unsigned,

				    const int);

drivers/block/drbd/drbd_receiver.c

+26 −21
Original line number Diff line number Diff line
@@ -2323,39 +2323,45 @@ out_interrupted: 
 * The current sync rate used here uses only the most recent two step marks,

 * to have a short time average so we can react faster.

 */

int drbd_rs_should_slow_down(struct drbd_device *device, sector_t sector)

bool drbd_rs_should_slow_down(struct drbd_device *device, sector_t sector)

{

	struct gendisk *disk = device->ldev->backing_bdev->bd_contains->bd_disk;

	unsigned long db, dt, dbdt;

	struct lc_element *tmp;

	int curr_events;

	int throttle = 0;

	unsigned int c_min_rate;



	rcu_read_lock();

	c_min_rate = rcu_dereference(device->ldev->disk_conf)->c_min_rate;

	rcu_read_unlock();

	bool throttle = true;



	/* feature disabled? */

	if (c_min_rate == 0)

		return 0;

	if (!drbd_rs_c_min_rate_throttle(device))

		return false;



	spin_lock_irq(&device->al_lock);

	tmp = lc_find(device->resync, BM_SECT_TO_EXT(sector));

	if (tmp) {

		struct bm_extent *bm_ext = lc_entry(tmp, struct bm_extent, lce);

		if (test_bit(BME_PRIORITY, &bm_ext->flags)) {

			spin_unlock_irq(&device->al_lock);

			return 0;

		}

		if (test_bit(BME_PRIORITY, &bm_ext->flags))

			throttle = false;

		/* Do not slow down if app IO is already waiting for this extent */

	}

	spin_unlock_irq(&device->al_lock);



	return throttle;

}



bool drbd_rs_c_min_rate_throttle(struct drbd_device *device)

{

	struct gendisk *disk = device->ldev->backing_bdev->bd_contains->bd_disk;

	unsigned long db, dt, dbdt;

	unsigned int c_min_rate;

	int curr_events;



	rcu_read_lock();

	c_min_rate = rcu_dereference(device->ldev->disk_conf)->c_min_rate;

	rcu_read_unlock();



	/* feature disabled? */

	if (c_min_rate == 0)

		return false;



	curr_events = (int)part_stat_read(&disk->part0, sectors[0]) +

		      (int)part_stat_read(&disk->part0, sectors[1]) -

			atomic_read(&device->rs_sect_ev);



	if (!device->rs_last_events || curr_events - device->rs_last_events > 64) {

		unsigned long rs_left;

		int i;
@@ -2378,12 +2384,11 @@ int drbd_rs_should_slow_down(struct drbd_device *device, sector_t sector) 
		dbdt = Bit2KB(db/dt);



		if (dbdt > c_min_rate)

			throttle = 1;

			return true;

	}

	return throttle;

	return false;

}





static int receive_DataRequest(struct drbd_connection *connection, struct packet_info *pi)

{

	struct drbd_peer_device *peer_device;

CRA Git | Maintained and supported by SUSTech CRA and CCSE