On Tue, Jan 23, 2024 at 09:49:42AM +0100, Christoph Hellwig wrote: > As we found out recently null_blk never splits bios in bio mode, thus > ignoring a lot of it's paramters and having buggy zoned device > handling. > > Is there any good reason to keep this mode around given that all relevant > hardware drivers use blk-mq, and the non-so-relevant ones not using > blk-mq probably should? The subject says removing the bio mode in null_blk but here you are asking an open question about the non-so-relevant ones should move to blk-mq. My input is for the latter part, FWIW. I tried to convert brd from bio to using blk-mq last year. One of the conclusion we reached was that we will see a performance hit when we use blk-mq for RAM backed devices because having tag management, etc was adding overhead to these drivers[1](You were also part of this discussion, so you probably remember it!). Unless there is a mode in blk-mq that can provide a real fast path for these drivers, moving to blk-mq might not be possible? [1] https://lore.kernel.org/linux-block/db1d7cd7-6c89-7d6b-3fe5-3778bb3cb5e9@xxxxxxxxx/ -- Pankaj Raghav
