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Another set of vdev queue optimizations.

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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
This commit is contained in:
Alexander Motin
2023-06-27 12:09:48 -04:00
committed by GitHub
parent 35a6247c5f
commit 8469b5aac0
8 changed files with 205 additions and 172 deletions
Download Patch File Download Diff File Expand all files Collapse all files
include/sys/zio.h
+12 -3
View File
@@ -436,6 +436,12 @@ typedef struct zio_link {
list_node_t zl_child_node;
} zio_link_t;
enum zio_qstate {
ZIO_QS_NONE = 0,
ZIO_QS_QUEUED,
ZIO_QS_ACTIVE,
};
struct zio {
/* Core information about this I/O */
zbookmark_phys_t io_bookmark;
@@ -479,6 +485,12 @@ struct zio {
const zio_vsd_ops_t *io_vsd_ops;
metaslab_class_t *io_metaslab_class; /* dva throttle class */
enum zio_qstate io_queue_state; /* vdev queue state */
union {
list_node_t l;
avl_node_t a;
} io_queue_node ____cacheline_aligned; /* allocator and vdev queues */
avl_node_t io_offset_node; /* vdev offset queues */
uint64_t io_offset;
hrtime_t io_timestamp; /* submitted at */
hrtime_t io_queued_timestamp;
@@ -486,9 +498,6 @@ struct zio {
hrtime_t io_delta; /* vdev queue service delta */
hrtime_t io_delay; /* Device access time (disk or */
/* file). */
avl_node_t io_queue_node;
avl_node_t io_offset_node;
avl_node_t io_alloc_node;
zio_alloc_list_t io_alloc_list;
/* Internal pipeline state */