On Mon, May 10, 2021 at 09:35:01PM -0400, Douglas Gilbert wrote: > On 2021-05-10 8:52 p.m., Ming Lei wrote: > > On Mon, May 03, 2021 at 06:22:13PM +0800, John Garry wrote: > > > The tags used for an IO scheduler are currently per hctx. > > > > > > As such, when q->nr_hw_queues grows, so does the request queue total IO > > > scheduler tag depth. > > > > > > This may cause problems for SCSI MQ HBAs whose total driver depth is > > > fixed. > > > > > > Ming and Yanhui report higher CPU usage and lower throughput in scenarios > > > where the fixed total driver tag depth is appreciably lower than the total > > > scheduler tag depth: > > > https://lore.kernel.org/linux-block/440dfcfc-1a2c-bd98-1161-cec4d78c6dfc@xxxxxxxxxx/T/#mc0d6d4f95275a2743d1c8c3e4dc9ff6c9aa3a76b > > > > > > > No difference any more wrt. fio running on scsi_debug with this patch in > > Yanhui's test machine: > > > > modprobe scsi_debug host_max_queue=128 submit_queues=32 virtual_gb=256 delay=1 > > vs. > > modprobe scsi_debug max_queue=128 submit_queues=1 virtual_gb=256 delay=1 > > > > Without this patch, the latter's result is 30% higher than the former's. > > > > note: scsi_debug's queue depth needs to be updated to 128 for avoiding io hang, > > which is another scsi issue. > > "scsi_debug: Fix cmd_per_lun, set to max_queue" made it into lk 5.13.0-rc1 as > commit fc09acb7de31badb2ea9e85d21e071be1a5736e4 . Is this the issue you are > referring to, or is there a separate issue in the wider scsi stack? OK, that is it, then it isn't necessary to update scsi_debug's queue depth for the test. Thanks, Ming
