Hi, It appears that task io accounting doesn't currently work when io_uring defers work to workqueues. E.g. while I get system wide "iostats -xm 1 /dev/sda" stats like: Device r/s w/s rMB/s wMB/s rrqm/s wrqm/s %rrqm %wrqm r_await w_await aqu-sz rareq-sz wareq-sz svctm %util sda 0.00 36475.00 0.00 250.52 0.00 660.00 0.00 1.78 0.00 0.14 0.00 0.00 7.03 0.03 99.70 "pidstat -d 1" as the user execution fio just shows 03:15:37 PM UID PID kB_rd/s kB_wr/s kB_ccwr/s iodelay Command 03:15:38 PM 0 13626 -1.00 -1.00 -1.00 53 kworker/u16:2-io_ring-wq 03:15:38 PM 0 13734 -1.00 -1.00 -1.00 51 kworker/u16:3+io_ring-write-wq 03:15:38 PM 0 13735 -1.00 -1.00 -1.00 53 kworker/u16:4+io_ring-wq 03:15:38 PM 0 13736 -1.00 -1.00 -1.00 50 kworker/u16:5-io_ring-wq 03:15:38 PM 0 13766 -1.00 -1.00 -1.00 52 kworker/u16:7-io_ring-wq 03:15:38 PM 0 13767 -1.00 -1.00 -1.00 51 kworker/u16:8-io_ring-write-wq 03:15:38 PM 0 13769 -1.00 -1.00 -1.00 51 kworker/u16:10+io_ring-wq and as root I get: 03:20:05 PM UID PID kB_rd/s kB_wr/s kB_ccwr/s iodelay Command 03:20:06 PM 0 13735 0.00 34344.00 0.00 49 kworker/u16:4+io_ring-wq 03:20:06 PM 0 13736 0.00 36080.00 0.00 47 kworker/u16:5+io_ring-wq 03:20:06 PM 0 13737 0.00 36624.00 0.00 43 kworker/u16:6+io_ring-wq 03:20:06 PM 0 13766 0.00 30616.00 0.00 50 kworker/u16:7+io_ring-wq 03:20:06 PM 0 13768 0.00 38728.00 0.00 47 kworker/u16:9+io_ring-wq 03:20:06 PM 0 13769 0.00 37792.00 0.00 51 kworker/u16:10+io_ring-wq 03:20:06 PM 0 13890 0.00 39176.00 0.00 47 kworker/u16:13+io_ring-wq and nothing is attributed to fio itself. For DIO I do get working task stats however. That is not all that surprising because tasks deferred to the workqueue won't properly be accounted for, because the page is dirtied from within the workqueue, rather than the normal process context. I suspect this doesn't just affect task io stats, but also means that io_uring writes will be able to escape writeback throttling, because presumably the workqueue kthreads are going to be throttled as individual tasks, rather than using causing the issuing process to be throttled. I assume this is a problem that needs to be fixed? Greetings, Andres Freund
