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From: Christoph Hellwig <hch@infradead.org>
To: Pavel Begunkov <asml.silence@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] iov_iter: optimise iter type checking
Date: Thu, 19 Nov 2020 17:03:40 +0000	[thread overview]
Message-ID: <20201119170340.GA6179@infradead.org> (raw)
In-Reply-To: <9bc27cb3ef6ab49b6b2ccee3db6613838aee17af.1605799583.git.asml.silence@gmail.com>

On Thu, Nov 19, 2020 at 03:29:43PM +0000, Pavel Begunkov wrote:
> The problem here is that iov_iter_is_*() helpers check types for
> equality, but all iterate_* helpers do bitwise ands. This confuses
> a compiler, so even if some cases were handled separately with
> iov_iter_is_*(), it can't eliminate and skip unreachable branches in
> following iterate*().

I think we need to kill the iov_iter_is_* helpers, renumber to not do
the pointless bitmask and just check for equality (might turn into a
bunch of nice switch statements actually).

  reply	other threads:[~2020-11-19 17:04 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-19 15:29 [PATCH 0/2] optimise iov_iter Pavel Begunkov
2020-11-19 15:29 ` [PATCH 1/2] iov_iter: optimise iov_iter_npages for bvec Pavel Begunkov
2020-11-19 15:29 ` [PATCH 2/2] iov_iter: optimise iter type checking Pavel Begunkov
2020-11-19 17:03   ` Christoph Hellwig [this message]
2020-11-19 17:12     ` Pavel Begunkov
2020-12-11  2:01       ` Al Viro
2020-12-13 22:32         ` Pavel Begunkov
2020-12-14 10:28           ` David Laight
2020-12-14 17:25             ` Pavel Begunkov
2020-11-19 16:46 ` [PATCH 0/2] optimise iov_iter Jens Axboe
2020-11-19 17:14   ` Pavel Begunkov
2020-11-19 17:20     ` Jens Axboe
2020-11-19 18:02       ` Pavel Begunkov

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