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| author | Lars Ellenberg <lars.ellenberg@linbit.com> | 2013-03-19 18:16:49 +0100 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2013-03-22 18:14:00 -0600 |
| commit | ebfd5d8f715167b886c9401e6b123847187f137b (patch) | |
| tree | 33da96fa4f1949af33492299930491f2ee797c9a /drivers/block/drbd | |
| parent | 56392d2f40aac4b520fc50bc356f40e07f7e1c7d (diff) | |
| download | linux-ebfd5d8f715167b886c9401e6b123847187f137b.tar.gz | |
drbd: drbd_al_being_io: short circuit to reduce latency
A request hitting an already "hot" extent should proceed right away, even if some other requests need to wait for pending transactions. Without that short-circuit, several simultaneous make_request contexts race for committing the transaction, possibly penalizing the innocent. Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com> Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'drivers/block/drbd')
| -rw-r--r-- | drivers/block/drbd/drbd_actlog.c | 14 |
1 files changed, 12 insertions, 2 deletions
diff --git a/drivers/block/drbd/drbd_actlog.c b/drivers/block/drbd/drbd_actlog.c index 82199d9a9a61..1d7244d2a910 100644 --- a/drivers/block/drbd/drbd_actlog.c +++ b/drivers/block/drbd/drbd_actlog.c @@ -256,6 +256,7 @@ void drbd_al_begin_io(struct drbd_conf *mdev, struct drbd_interval *i, bool dele unsigned first = i->sector >> (AL_EXTENT_SHIFT-9); unsigned last = i->size == 0 ? first : (i->sector + (i->size >> 9) - 1) >> (AL_EXTENT_SHIFT-9); unsigned enr; + bool need_transaction = false; bool locked = false; /* When called through generic_make_request(), we must delegate @@ -273,8 +274,17 @@ void drbd_al_begin_io(struct drbd_conf *mdev, struct drbd_interval *i, bool dele D_ASSERT(first <= last); D_ASSERT(atomic_read(&mdev->local_cnt) > 0); - for (enr = first; enr <= last; enr++) - wait_event(mdev->al_wait, _al_get(mdev, enr) != NULL); + for (enr = first; enr <= last; enr++) { + struct lc_element *al_ext; + wait_event(mdev->al_wait, (al_ext = _al_get(mdev, enr)) != NULL); + if (al_ext->lc_number != enr) + need_transaction = true; + } + + /* If *this* request was to an already active extent, + * we're done, even if there are pending changes. */ + if (!need_transaction) + return; /* Serialize multiple transactions. * This uses test_and_set_bit, memory barrier is implicit. |