From: David Laight <David.Laight@ACULAB.COM>
To: 'Pavel Begunkov' <asml.silence@gmail.com>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <axboe@kernel.dk>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH v2 1/2] iov_iter: optimise iov_iter_npages for bvec
Date: Fri, 20 Nov 2020 13:29:14 +0000 [thread overview]
Message-ID: <e8067cc132b449b9b0e910622b5210ad@AcuMS.aculab.com> (raw)
In-Reply-To: <ab04202d0f8c1424da47251085657c436d762785.1605827965.git.asml.silence@gmail.com>
From: Pavel Begunkov
> Sent: 19 November 2020 23:25
>
> The block layer spends quite a while in iov_iter_npages(), but for the
> bvec case the number of pages is already known and stored in
> iter->nr_segs, so it can be returned immediately as an optimisation
>
> Perf for an io_uring benchmark with registered buffers (i.e. bvec) shows
> ~1.5-2.0% total cycle count spent in iov_iter_npages(), that's dropped
> by this patch to ~0.2%.
>
> Reviewed-by: Jens Axboe <axboe@kernel.dk>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
> lib/iov_iter.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index 1635111c5bd2..0fa7ac330acf 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -1594,6 +1594,8 @@ int iov_iter_npages(const struct iov_iter *i, int maxpages)
> return 0;
> if (unlikely(iov_iter_is_discard(i)))
> return 0;
> + if (unlikely(iov_iter_is_bvec(i)))
> + return min_t(int, i->nr_segs, maxpages);
>
> if (unlikely(iov_iter_is_pipe(i))) {
Is it worth putting an extra condition around these three 'unlikely' cases.
ie:
if (unlikely((iov_iter_type(i) & (ITER_DISCARD | ITER_BVEC | ITER_PIPE)) {
if (iov_iter_is_discard(i))
return 0;
if (iov_iter_is_bvec(i))
return min_t(int, i->nr_segs, maxpages);
/* Must be ITER_PIPE */
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2020-11-20 13:29 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 [this message]
2020-11-19 23:24 ` [PATCH v2 2/2] iov_iter: optimise iter type checking Pavel Begunkov
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