Re: [PATCH] blk-mq: Use request queue-wide tags for tagset-wide sbitmap

[John Garry]

On 11/05/2021 01:52, Ming Lei wrote:
> > 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.

ok, good. I'll post a v2 with comments addressed.

> note: scsi_debug's queue depth needs to be updated to 128 for avoiding io hang,
> which is another scsi issue.
I was just carrying Doug's patch to test.

Thanks,
John