From: Mike Snitzer <snitzer@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, dm-devel@redhat.com,
linux-bcache@vger.kernel.org
Subject: Re: [PATCH 3/3] block: bypass ->make_request_fn for blk-mq drivers
Date: Tue, 28 Apr 2020 14:40:47 -0400 [thread overview]
Message-ID: <20200428184047.GB17609@redhat.com> (raw)
In-Reply-To: <20200425075336.721021-4-hch@lst.de>
On Sat, Apr 25 2020 at 3:53am -0400,
Christoph Hellwig <hch@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@lst.de>
Makes me cringe thinking about all the indirect calls sprinkled
throughout DM...
Acked-by: Mike Snitzer <snitzer@redhat.com>
next prev parent reply other threads:[~2020-04-28 18:40 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-25 7:53 avoid the ->make_request_fn indirect for blk-mq drivers Christoph Hellwig
2020-04-25 7:53 ` [PATCH 1/3] bcache: remove a duplicate ->make_request_fn assignment Christoph Hellwig
2020-04-26 9:35 ` Coly Li
2020-04-25 7:53 ` [PATCH 2/3] dm: remove the make_request_fn check in device_area_is_invalid Christoph Hellwig
2020-04-28 18:38 ` Mike Snitzer
2020-04-25 7:53 ` [PATCH 3/3] block: bypass ->make_request_fn for blk-mq drivers Christoph Hellwig
2020-04-28 18:40 ` Mike Snitzer [this message]
2020-04-25 15:45 ` avoid the ->make_request_fn indirect " Jens Axboe
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