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

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Date:   Fri, 8 Jul 2022 01:04:44 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Sergei Shtepa <sergei.shtepa@...am.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 15/20] block, blksnap: snapshot image block device

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).