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Date:   Fri, 15 Oct 2021 21:30:48 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Subject: Re: [PATCH] block: use flags instead of bit fields for blkdev_dio
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On Thu, Oct 14, 2021 at 12:34:55PM -0600, Jens Axboe wrote:
> This generates a lot better code for me, and bumps performance from
> 7650K IOPS to 7750K IOPS. Looking at profiles for the run and running
> perf diff, it confirms that we're now sending a lot less time there:
> 
>      6.38%     -2.80%  [kernel.vmlinux]  [k] blkdev_direct_IO
> 
> Taking it from the 2nd most cycle consumer to only the 9th most at
> 3.35% of the CPU time.

Kinda weird that the overhead is so big.  That being said for more
than a single flag I prefer the bit ops anyway, this code just
"evolved".

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