Since currently we have no simple but efficient way to implement the bio-based IO polling in the split-bio tracking style, this patch set turns to the original implementation mechanism that iterates and polls all underlying hw queues in polling mode. One optimization is introduced to mitigate the race of one hw queue among multiple polling instances. I'm still open to the split bio tracking mechanism, if there's reasonable way to implement it. [Performance Test] The performance is tested by fio (engine=io_uring) 4k randread on dm-linear device. The dm-linear device is built upon nvme devices, and every nvme device has one polling hw queue (nvme.poll_queues=1). Test Case | IOPS in IRQ mode | IOPS in polling mode | Diff | (hipri=0) | (hipri=1) | --------------------------- | ---------------- | -------------------- | ---- 3 target nvme, num_jobs = 1 | 198k | 276k | ~40% 3 target nvme, num_jobs = 3 | 608k | 705k | ~16% 6 target nvme, num_jobs = 6 | 1197k | 1347k | ~13% 3 target nvme, num_jobs = 6 | 1285k | 1293k | ~0% As the number of polling instances (num_jobs) increases, the performance improvement decreases, though it's still positive compared to the IRQ mode. [Optimization] To mitigate the race when iterating all the underlying hw queues, one flag is maintained on a per-hw-queue basis. This flag is used to indicate whether this polling hw queue currently being polled on or not. Every polling hw queue is exclusive to one polling instance, i.e., the polling instance will skip this polling hw queue if this hw queue currently is being polled by another polling instance, and start polling on the next hw queue. This per-hw-queue flag map is currently maintained in dm layer. In the table load phase, a table describing all underlying polling hw queues is built and stored in 'struct dm_table'. It is safe when reloading the mapping table. changes since v1: - patch 1,2,4 is the same as v1 and have already been reviewed - patch 3 is refactored a bit on the basis of suggestions from Mike Snitzer. - patch 5 is newly added and introduces one new queue flag representing if the queue is capable of IO polling. This mainly simplifies the logic in queue_poll_store(). - patch 6 implements the core mechanism supporting IO polling. The sanity check checking if the dm device supports IO polling is also folded into this patch, and the queue flag will be cleared if it doesn't support, in case of table reloading. Jeffle Xu (6): block: move definition of blk_qc_t to types.h block: add queue_to_disk() to get gendisk from request_queue block: add iopoll method to support bio-based IO polling dm: always return BLK_QC_T_NONE for bio-based device block: add QUEUE_FLAG_POLL_CAP flag dm: support IO polling for bio-based dm device block/blk-core.c | 76 +++++++++++++++++++++ block/blk-mq.c | 76 +++------------------ block/blk-sysfs.c | 3 +- drivers/md/dm-core.h | 21 ++++++ drivers/md/dm-table.c | 127 +++++++++++++++++++++++++++++++++++ drivers/md/dm.c | 61 ++++++++++++----- include/linux/blk-mq.h | 3 + include/linux/blk_types.h | 2 +- include/linux/blkdev.h | 9 +++ include/linux/fs.h | 2 +- include/linux/types.h | 3 + include/trace/events/kyber.h | 6 +- 12 files changed, 302 insertions(+), 87 deletions(-) -- 2.27.0 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
