On Fri, Feb 17, 2023 at 08:22:15PM +0530, Pankaj Raghav wrote:

I will park this effort as blk-mq doesn't improve the performance for brd,
and we can retain the submit_bio interface.

I am not sure if the feedback was intended to suggest we shouldn't do
the blk-mq conversion, but rather explain why in some workloads it
may not be as good as the old submit_bio() interface. Probably low
hanging fruit, if we *really* wanted to provide parity for the odd
workloads.

If we *mostly*  we see better performance with blk-mq it would seem
likely reasonable to merge. Dozens of drivers were converted to blk-mq
and *most* without *any* performance justification on them. I think
ming's was the commit log that had the most elaborate performacne
metrics and I think it also showed some *minor* slowdown on some
workloads, but the dramatic gains made it worthwhile.

Most of the conversions to blk-mq didn't even have *any* metrics posted.

  Luis