On Wed, Apr 14, 2021 at 04:12:22PM +0530, Kashyap Desai 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. > > I can also recreate this issue using mq-deadline. Using <none>, there is no > IO hang issue. > Also if I run script to change scheduler periodically (none, mq-deadline), > sysfs entry hangs. > > Here is call trace- > Call Trace: > [ 1229.879862] __schedule+0x29d/0x7a0 > [ 1229.879871] schedule+0x3c/0xa0 > [ 1229.879875] blk_mq_freeze_queue_wait+0x62/0x90 > [ 1229.879880] ? finish_wait+0x80/0x80 > [ 1229.879884] elevator_switch+0x12/0x40 > [ 1229.879888] elv_iosched_store+0x79/0x120 > [ 1229.879892] ? kernfs_fop_write_iter+0xc7/0x1b0 > [ 1229.879897] queue_attr_store+0x42/0x70 > [ 1229.879901] kernfs_fop_write_iter+0x11f/0x1b0 > [ 1229.879905] new_sync_write+0x11f/0x1b0 > [ 1229.879912] vfs_write+0x184/0x250 > [ 1229.879915] ksys_write+0x59/0xd0 > [ 1229.879917] do_syscall_64+0x33/0x40 > [ 1229.879922] entry_SYSCALL_64_after_hwframe+0x44/0xae > > > I tried both - 5.12.0-rc1 and 5.11.0-rc2+ and there is a same behavior. > Let me also check megaraid_sas and see if anything generic or this is a > special case of scsi_debug. As I mentioned, it could be one generic issue wrt. SCHED_RESTART. shared tags might have to restart all hctx since all share same tags. Thanks, Ming
