Re: [PATCH 15/20] block, blksnap: snapshot image block device

[Christoph Hellwig]

On Fri, Jul 08, 2022 at 09:58:25AM +0200, Sergei Shtepa wrote:
> There was a goal to use the kernel innovations whenever possible.
> Of course, it makes sense to return to bio based if it allows to
> achieve better performance. This is not a matter of principle.

In general blk-mq is designed for hardware drivers, while the
bio based interface is for stacking drivers.  There are some
exceptions: dm-mpath is a stacking blk-mq driver, but one that
just passes I/O through, and there is a bunch of hardware drivers
implemented as bio based ones, although I suspect most of them
would end up being improved by switching to blk-mq (or in most
case by just deleting them).