On Wed, Apr 14, 2021 at 11:10:39AM +0100, John Garry wrote: > Hi Ming, > > > > > It is reported inside RH that CPU utilization is increased ~20% when > > running simple FIO test inside VM which disk is built on image stored > > on XFS/megaraid_sas. > > > > When I try to investigate by reproducing the issue via scsi_debug, I found > > IO hang when running randread IO(8k, direct IO, libaio) on scsi_debug disk > > created by the following command: > > > > modprobe scsi_debug host_max_queue=128 submit_queues=$NR_CPUS virtual_gb=256 > > > > So I can recreate this hang for using mq-deadline IO sched for scsi debug, > in that fio does not exit. I'm using v5.12-rc7. > > Do you have any idea of what changed to cause this, as we would have tested > this before? Or maybe only none IO sched on scsi_debug. And normally 4k > block size and only rw=read (for me, anyway). Just run a quick test with none on scsi_debug, looks the issue can't be reproduced, but very worse performance is observed with none(20% IOPS drops, and 50% CPU utilization increased). > > Note that host_max_queue=128 will cap submit queue depth at 128, while would > be 192 by default. I take 128 because the reported megaraid_sas's host queue depth is 128. Thanks, Ming
