From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Philipp Reisner To: linux-kernel@vger.kernel.org Date: Tue, 19 Mar 2013 18:16:49 +0100 Message-Id: <1363713419-17803-9-git-send-email-philipp.reisner@linbit.com> In-Reply-To: <1363713419-17803-1-git-send-email-philipp.reisner@linbit.com> References: <1363713419-17803-1-git-send-email-philipp.reisner@linbit.com> Cc: Jens Axboe , lars.ellenberg@linbit.com, drbd-dev@lists.linbit.com Subject: [Drbd-dev] [PATCH 08/18] drbd: drbd_al_being_io: short circuit to reduce latency List-Id: "*Coordination* of development, patches, contributions -- *Questions* \(even to developers\) go to drbd-user, please." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Lars Ellenberg 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 Signed-off-by: Lars Ellenberg --- drivers/block/drbd/drbd_actlog.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/drivers/block/drbd/drbd_actlog.c b/drivers/block/drbd/drbd_actlog.c index 82199d9..1d7244d 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. -- 1.7.9.5