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. Thanks, Ming
