From 50b25b2187134ac7b19cf93bd35a420223f1d343 Mon Sep 17 00:00:00 2001 From: Brian Behlendorf Date: Tue, 5 Aug 2014 13:57:59 -0700 Subject: [PATCH] Avoid dynamic allocation of 'search zio' As part of commit e8b96c6 the search zio used by the vdev_queue_io_to_issue() function was moved to the heap to minimize stack usage. Functionally this is fine, but to maximize performance it's best to minimize the number of dynamic allocations. To avoid this allocation temporary space for the search zio has been reserved in the vdev_queue structure. All access must be serialized through the vq_lock. Signed-off-by: Brian Behlendorf Signed-off-by: Ned Bass Closes #2572 --- include/sys/vdev_impl.h | 1 + module/zfs/vdev_queue.c | 10 ++++------ 2 files changed, 5 insertions(+), 6 deletions(-) diff --git a/include/sys/vdev_impl.h b/include/sys/vdev_impl.h index 16cf4d770..16fcaa042 100644 --- a/include/sys/vdev_impl.h +++ b/include/sys/vdev_impl.h @@ -118,6 +118,7 @@ struct vdev_queue { hrtime_t vq_io_complete_ts; /* time last i/o completed */ hrtime_t vq_io_delta_ts; list_t vq_io_list; + zio_t vq_io_search; /* used as local for stack reduction */ kmutex_t vq_lock; }; diff --git a/module/zfs/vdev_queue.c b/module/zfs/vdev_queue.c index 0dc733efc..e2758d1c4 100644 --- a/module/zfs/vdev_queue.c +++ b/module/zfs/vdev_queue.c @@ -659,7 +659,6 @@ vdev_queue_io_to_issue(vdev_queue_t *vq) zio_priority_t p; avl_index_t idx; vdev_queue_class_t *vqc; - zio_t *search; again: ASSERT(MUTEX_HELD(&vq->vq_lock)); @@ -678,11 +677,10 @@ again: * For FIFO queues (sync), issue the i/o with the lowest timestamp. */ vqc = &vq->vq_class[p]; - search = zio_buf_alloc(sizeof (*search)); - search->io_timestamp = 0; - search->io_offset = vq->vq_last_offset + 1; - VERIFY3P(avl_find(&vqc->vqc_queued_tree, search, &idx), ==, NULL); - zio_buf_free(search, sizeof (*search)); + vq->vq_io_search.io_timestamp = 0; + vq->vq_io_search.io_offset = vq->vq_last_offset + 1; + VERIFY3P(avl_find(&vqc->vqc_queued_tree, &vq->vq_io_search, + &idx), ==, NULL); zio = avl_nearest(&vqc->vqc_queued_tree, idx, AVL_AFTER); if (zio == NULL) zio = avl_first(&vqc->vqc_queued_tree);