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8469b5aac0
Switch FIFO queues (SYNC/TRIM) and active queue of vdev queue from time-sorted AVL-trees to simple lists. AVL-trees are too expensive for such a simple task. To change I/O priority without searching through the trees, add io_queue_state field to struct zio. To not check number of queued I/Os for each priority add vq_cqueued bitmap to struct vdev_queue. Update it when adding/removing I/Os. Make vq_cactive a separate array instead of struct vdev_queue_class member. Together those allow to avoid lots of cache misses when looking for work in vdev_queue_class_to_issue(). Introduce deadline of ~0.5s for LBA-sorted queues. Before this I saw some I/Os waiting in a queue for up to 8 seconds and possibly more due to starvation. With this change I no longer see it. I had to slightly more complicate the comparison function, but since it uses all the same cache lines the difference is minimal. For a sequential I/Os the new code in vdev_queue_io_to_issue() actually often uses more simple avl_first(), falling back to avl_find() and avl_nearest() only when needed. Arrange members in struct zio to access only one cache line when searching through vdev queues. While there, remove io_alloc_node, reusing the io_queue_node instead. Those two are never used same time. Remove zfs_vdev_aggregate_trim parameter. It was disabled for 4 years since implemented, while still wasted time maintaining the offset-sorted tree of TRIM requests. Just remove the tree. Remove locking from txg_all_lists_empty(). It is racy by design, while 2 pair of locks/unlocks take noticeable time under the vdev queue lock. With these changes in my tests with volblocksize=4KB I measure vdev queue lock spin time reduction by 50% on read and 75% on write. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Sponsored by: iXsystems, Inc. Closes #14925 |
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