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

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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: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Lars Ellenberg 2014-04-28 18:43:19 +02:00 committed by Jens Axboe
parent 0e49d7b014
commit e829987433
3 changed files with 34 additions and 29 deletions
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13
drivers/block/drbd/drbd_actlog.c
View File

@ -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;
}
}

3
drivers/block/drbd/drbd_int.h
View File

@ -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);

47
drivers/block/drbd/drbd_receiver.c
View File

@ -2323,14 +2323,33 @@ 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 lc_element *tmp;
bool throttle = true;
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))
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;
struct lc_element *tmp;
int curr_events;
int throttle = 0;
unsigned int c_min_rate;
int curr_events;
rcu_read_lock();
c_min_rate = rcu_dereference(device->ldev->disk_conf)->c_min_rate;
@ -2338,24 +2357,11 @@ int drbd_rs_should_slow_down(struct drbd_device *device, sector_t sector)
/* feature disabled? */
if (c_min_rate == 0)
return 0;
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;
}
/* Do not slow down if app IO is already waiting for this extent */
}
spin_unlock_irq(&device->al_lock);
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;