[dm-devel] [PATCH 3/3] block: bypass ->make_request_fn for blk-mq drivers

[Mike Snitzer]

On Sat, Apr 25 2020 at  3:53am -0400,
Christoph Hellwig <hch at lst.de> wrote:

> Call blk_mq_make_request when no ->make_request_fn is set.  This is
> safe now that blk_alloc_queue always sets up the pointer for make_request
> based drivers.  This avoids an indirect call in the blk-mq driver I/O
> fast path, which is rather expensive due to spectre mitigations.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>

Makes me cringe thinking about all the indirect calls sprinkled
throughout DM...

Acked-by: Mike Snitzer <snitzer at redhat.com>