drbd: Implemented side-stepping in drbd_res_begin_io()
Before:
drbd_rs_begin_io() locked app-IO out of an RS extent, and
waited then until all previous app-IO in that area finished.
(But not only until the disk-IO was finished but until the
barrier/epoch ack came in for that == round trip time latency ++)
After:
As soon as a new app-IO waits wants to start new IO on that
RS extent, drbd_rs_begin_io() steps aside (clearing the
BME_NO_WRITES flag again). It retries after 100ms.
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
diff --git a/drivers/block/drbd/drbd_actlog.c b/drivers/block/drbd/drbd_actlog.c
index 28f85d9..5570d9b 100644
--- a/drivers/block/drbd/drbd_actlog.c
+++ b/drivers/block/drbd/drbd_actlog.c
@@ -176,14 +176,17 @@
struct lc_element *al_ext;
struct lc_element *tmp;
unsigned long al_flags = 0;
+ int wake;
spin_lock_irq(&mdev->al_lock);
tmp = lc_find(mdev->resync, enr/AL_EXT_PER_BM_SECT);
if (unlikely(tmp != NULL)) {
struct bm_extent *bm_ext = lc_entry(tmp, struct bm_extent, lce);
if (test_bit(BME_NO_WRITES, &bm_ext->flags)) {
- set_bit(BME_PRIORITY, &bm_ext->flags);
+ wake = !test_and_set_bit(BME_PRIORITY, &bm_ext->flags);
spin_unlock_irq(&mdev->al_lock);
+ if (wake)
+ wake_up(&mdev->al_wait);
return NULL;
}
}
@@ -1135,7 +1138,10 @@
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. */
+retry:
sig = wait_event_interruptible(mdev->al_wait,
(bm_ext = _bme_get(mdev, enr)));
if (sig)
@@ -1146,16 +1152,24 @@
for (i = 0; i < AL_EXT_PER_BM_SECT; i++) {
sig = wait_event_interruptible(mdev->al_wait,
- !_is_in_al(mdev, enr * AL_EXT_PER_BM_SECT + i));
- if (sig) {
+ !_is_in_al(mdev, enr * AL_EXT_PER_BM_SECT + i) ||
+ (test_bit(BME_PRIORITY, &bm_ext->flags) && sa));
+
+ if (sig || (test_bit(BME_PRIORITY, &bm_ext->flags) && sa)) {
spin_lock_irq(&mdev->al_lock);
if (lc_put(mdev->resync, &bm_ext->lce) == 0) {
- clear_bit(BME_NO_WRITES, &bm_ext->flags);
+ bm_ext->flags = 0; /* clears BME_NO_WRITES and eventually BME_PRIORITY */
mdev->resync_locked--;
wake_up(&mdev->al_wait);
}
spin_unlock_irq(&mdev->al_lock);
- return -EINTR;
+ if (sig)
+ return -EINTR;
+ if (schedule_timeout_interruptible(HZ/10))
+ return -EINTR;
+ if (--sa == 0)
+ dev_warn(DEV,"drbd_rs_begin_io() no longer stepping aside.\n");
+ goto retry;
}
}
set_bit(BME_LOCKED, &bm_ext->flags);