linux-kernel - Re: [PATCH v2 3/3] blk-mq: optimise *end

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Message-ID: <YWb7ikSx6vz03u6B@infradead.org>
Date:   Wed, 13 Oct 2021 16:30:18 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Pavel Begunkov <asml.silence@...il.com>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH v2 3/3] blk-mq: optimise *end_request non-stat path

On Wed, Oct 13, 2021 at 09:57:13AM +0100, Pavel Begunkov wrote:
> We already have a blk_mq_need_time_stamp() check in
> __blk_mq_end_request() to get a timestamp, hide all the statistics
> accounting under it. It cuts some cycles for requests that don't need
> stats, and is free otherwise.

The transformation is a little non-obvious due to the checks hidden
inblk_mq_need_time_stamp, but after following all the spaghetti it does
looks like a correct transformation:

Reviewed-by: Christoph Hellwig <hch@....de>