Hi fio community, On 4.x kernels we used to be able to do: # echo 1 > /sys/block/nvme0n1/queue/io_poll And then run a polled_io job in fio with pvsync2 as our ioengine, with the hipri flag set. On 5.x kernels we see the following error trying to write the device settings>>> -bash: echo: write error: Invalid argument This is verifiable on 5.3, 5.4 kernels with fio 3.16 builds. What is the background on what has changed because Jens wrote this note back in 2015, which did work once upon a time. But now things have changed, but none of us here in the Intel SSD group and OSS Driver team really know why. https://lwn.net/Articles/663543/ More documentation can be found here: https://stackoverflow.com/questions/55223883/echo-write-error-invalid-argument-while-setting-io-poll-for-nvme-ssd/ Here is a good sample A / B test: [global] direct=1 filename=/dev/nvme1n1 log_avg_msec=500 time_based percentile_list=1:5:10:20:30:40:50:60:70:80:90:95:99:99.5:99.9:99.95:99.99:99.999:99.9999 [rand-read-4k-qd1] runtime=120 bs=4K iodepth=1 numjobs=1 cpus_allowed=0 ioengine=io_uring hipri rw=randread Works! [global] direct=1 filename=/dev/nvme1n1 log_avg_msec=500 time_based percentile_list=1:5:10:20:30:40:50:60:70:80:90:95:99:99.5:99.9:99.95:99.99:99.999:99.9999 [rand-read-4k-qd1] runtime=120 bs=4K iodepth=1 numjobs=1 cpus_allowed=0 ioengine=pvsync2 hipri rw=randread Does not work... you do not see the CPU spin up to 100% (kernel/sys usage) on hipri with pvsync2 on a 5.x kernel. Why not? And what changed here? Is it possible to get a new LWN article? Thank you! Frank Ober
