On Tue, Oct 25, 2022 at 11:15:57AM +0800, Ziyang Zhang wrote: > On 2022/10/24 21:20, Ming Lei wrote: > > Hello Ziyang, > > > > On Mon, Oct 24, 2022 at 05:48:51PM +0800, Ziyang Zhang wrote: > >> On 2022/10/23 17:38, Ming Lei wrote: > >>> task_work_add() is used for waking ubq daemon task with one batch > >>> of io requests/commands queued. However, task_work_add() isn't > >>> exported for module code, and it is still debatable if the symbol > >>> should be exported. > >>> > >>> Fortunately we still have io_uring_cmd_complete_in_task() which just > >>> can't handle batched wakeup for us. > >>> > >>> Add one one llist into ublk_queue and call io_uring_cmd_complete_in_task() > >>> via current command for running them via task work. > >>> > >>> This way cleans up current code a lot, meantime allow us to wakeup > >>> ubq daemon task after queueing batched requests/io commands. > >>> > >> > >> > >> Hi, Ming > >> > >> This patch works and I have run some tests to compare current version(ucmd) > >> with your patch(ucmd-batch). > >> > >> iodepth=128 numjobs=1 direct=1 bs=4k > >> > >> -------------------------------------------- > >> ublk loop target, the backend is a file. > >> IOPS(k) > >> > >> type ucmd ucmd-batch > >> seq-read 54.7 54.2 > >> rand-read 52.8 52.0 > >> > >> -------------------------------------------- > >> ublk null target > >> IOPS(k) > >> > >> type ucmd ucmd-batch > >> seq-read 257 257 > >> rand-read 252 253 > >> > >> > >> I find that io_req_task_work_add() puts task_work node into a llist > >> first, then it may call task_work_add() to run batched task_works. So do we really > >> need such llist in ublk_drv? I think io_uring has already considered task_work batch > >> optimization. > >> > >> BTW, task_work_add() in ublk_drv achieves > >> higher IOPS(about 5-10% on my machine) than io_uring_cmd_complete_in_task() > >> in ublk_drv. > > > > Yeah, that is same with my observation, and motivation of this patch is > > to get same performance with task_work_add by building ublk_drv as > > module. One win of task_work_add() is that we get exact batching info > > meantime only send TWA_SIGNAL_NO_IPI for whole batch, that is basically > > what the patch is doing, but needs help of the following ublksrv patch: > > > > https://github.com/ming1/ubdsrv/commit/dce6d1d222023c1641292713b311ced01e6dc548 > > > > which sets IORING_SETUP_COOP_TASKRUN for ublksrv's uring, then > > io_uring_cmd_complete_in_task will notify via TWA_SIGNAL_NO_IPI, and 5+% > > IOPS boost is observed on loop/001 by putting image on SSD in my test > > VM. > > Hi Ming, > > I have added this ublksrv patch and run the above test again. > I have also run ublksrv test: loop/001. Please check them. > > Intel(R) Xeon(R) Platinum 8369B CPU @ 2.70GHz 16 cores > 64GB MEM, CentOS 8, kernel 6.0+ > > -------- > fio test > > iodepth=128 numjobs=1 direct=1 bs=4k > > ucmd: without your kernel patch. Run io_uring_cmd_complete_in_task() > for each blk-mq rq. > > ucmd-batch: with your kernel patch. Run io_uring_cmd_complete_in_task() > for the last blk-mq rq. > > -------------------------------------------- > ublk loop target, the backend is a file. > > IOPS(k) > > type ucmd ucmd-batch > seq-read 54.1 53.7 > rand-read 52.0 52.0 > > -------------------------------------------- > ublk null target > IOPS(k) > > type ucmd ucmd-batch > seq-read 272 265 > rand-read 262 260 > > ------------ > ublksrv test > > ------------- > ucmd > > running loop/001 > fio (ublk/loop( -f /root/work/ubdsrv/tests/tmp/ublk_loop_1G_BZ85U), libaio, bs 4k, dio, hw queues:1, uring_comp: 0, get_data: 0)... > randwrite: jobs 1, iops 66737 > randread: jobs 1, iops 64935 > randrw: jobs 1, iops read 32694 write 32710 > rw(512k): jobs 1, iops read 772 write 819 > > ------------- > ucmd-batch > > running loop/001 > fio (ublk/loop( -f /root/work/ubdsrv/tests/tmp/ublk_loop_1G_F56a3), libaio, bs 4k, dio, hw queues:1, uring_comp: 0, get_data: 0)... > randwrite: jobs 1, iops 66720 > randread: jobs 1, iops 65015 > randrw: jobs 1, iops read 32743 write 32759 > rw(512k): jobs 1, iops read 771 write 817 > > > It seems that manually putting rqs into llist and calling > io_uring_cmd_complete_in_task() while handling the last rq does > not improve IOPS much. > > io_req_task_work_add() puts task_work node into a internal llist > first, then it may call task_work_add() to run batched task_works. > IMO, io_uring has already done such batch optimization and ublk_drv > does not need to add such llist. The difference is just how batching is handled, looks blk-mq's batch info doesn't matter any more. In my test, looks the perf improvement is mainly made by enabling IORING_SETUP_COOP_TASKRUN in ublksrv. Can you check if enabling IORING_SETUP_COOP_TASKRUN only can reach same perf with task_work_add()(ublk_drv is builtin) when building ublk_drv as module? Thanks, Ming
