On 1/28/21 1:19 AM, Mike Snitzer wrote: > On Mon, Jan 25 2021 at 7:13am -0500, > Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx> wrote: > >> 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. > > I think there is serious room for improvement for DM's implementation; > but the block changes for this are all we'd need for DM in the longrun > anyway (famous last words). Agreed. > So on a block interface level I'm OK with > block patches 1-3. > > I don't see why patch 5 is needed (said the same in reply to it; but I > just saw your reason below..). > > Anyway, I can pick up DM patches 4 and 6 via linux-dm.git if Jens picks > up patches 1-3. Jens, what do you think? cc Jens. Also I will send a new version later, maybe some refactor on patch5 and some typo modifications. > >> [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(). > > Ah OK, don't see why we want to eat a queue flag for that though! > >> - 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. > > Thanks, > Mike > -- Thanks, Jeffle
