From: Pavel Begunkov <asml.silence@gmail.com>
To: linux-fsdevel@vger.kernel.org, Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2 2/2] iov_iter: optimise iter type checking
Date: Thu, 19 Nov 2020 23:24:39 +0000 [thread overview]
Message-ID: <70d65e06b22cfb11f70b92c12c4d176f36b0e646.1605827965.git.asml.silence@gmail.com> (raw)
In-Reply-To: <cover.1605827965.git.asml.silence@gmail.com>
The problem here is that iov_iter_is_*() helpers check types for
equality, but all iterate_* helpers do bitwise ands. This confuses
compilers, so even if some cases were handled separately with
iov_iter_is_*(), corresponding ifs in iterate*() right after are not
eliminated.
E.g. iov_iter_npages() first handles bvecs and discards, but
iterate_all_kinds() still checks those iter types and generates actually
unreachable code including iter init, for(), etc.
size lib/iov_iter.o
before:
text data bss dec hex filename
24409 805 0 25214 627e lib/iov_iter.o
after:
text data bss dec hex filename
23785 793 0 24578 6002 lib/iov_iter.o
Most of it is ifs that are executed but never true.
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
include/linux/uio.h | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/include/linux/uio.h b/include/linux/uio.h
index 72d88566694e..c5970b2d3307 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -57,27 +57,27 @@ static inline enum iter_type iov_iter_type(const struct iov_iter *i)
static inline bool iter_is_iovec(const struct iov_iter *i)
{
- return iov_iter_type(i) == ITER_IOVEC;
+ return iov_iter_type(i) & ITER_IOVEC;
}
static inline bool iov_iter_is_kvec(const struct iov_iter *i)
{
- return iov_iter_type(i) == ITER_KVEC;
+ return iov_iter_type(i) & ITER_KVEC;
}
static inline bool iov_iter_is_bvec(const struct iov_iter *i)
{
- return iov_iter_type(i) == ITER_BVEC;
+ return iov_iter_type(i) & ITER_BVEC;
}
static inline bool iov_iter_is_pipe(const struct iov_iter *i)
{
- return iov_iter_type(i) == ITER_PIPE;
+ return iov_iter_type(i) & ITER_PIPE;
}
static inline bool iov_iter_is_discard(const struct iov_iter *i)
{
- return iov_iter_type(i) == ITER_DISCARD;
+ return iov_iter_type(i) & ITER_DISCARD;
}
static inline unsigned char iov_iter_rw(const struct iov_iter *i)
--
2.24.0
prev parent reply other threads:[~2020-11-19 23:28 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-19 23:24 [PATCH v2 0/2] optimise iov_iter Pavel Begunkov
2020-11-19 23:24 ` [PATCH v2 1/2] iov_iter: optimise iov_iter_npages for bvec Pavel Begunkov
2020-11-20 1:20 ` Matthew Wilcox
2020-11-20 1:39 ` Pavel Begunkov
2020-11-20 1:49 ` Matthew Wilcox
2020-11-20 1:56 ` Pavel Begunkov
2020-11-20 2:06 ` Matthew Wilcox
2020-11-20 2:08 ` Pavel Begunkov
2020-11-20 2:24 ` Ming Lei
2020-11-20 17:22 ` Pavel Begunkov
2020-11-20 17:23 ` Pavel Begunkov
2020-11-20 2:22 ` Ming Lei
2020-11-20 2:25 ` Pavel Begunkov
2020-11-20 2:54 ` Matthew Wilcox
2020-11-20 8:14 ` Christoph Hellwig
2020-11-20 12:39 ` Matthew Wilcox
2020-11-20 13:00 ` Pavel Begunkov
2020-11-20 13:13 ` Matthew Wilcox
2020-11-20 9:57 ` Pavel Begunkov
2020-11-20 13:29 ` David Laight
2020-11-19 23:24 ` Pavel Begunkov [this message]
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