From: David Laight <[email protected]>
To: 'Pavel Begunkov' <[email protected]>,
"[email protected]" <[email protected]>
Cc: Jens Axboe <[email protected]>,
Christoph Hellwig <[email protected]>,
Matthew Wilcox <[email protected]>,
Ming Lei <[email protected]>,
Johannes Weiner <[email protected]>,
Alexander Viro <[email protected]>,
"Darrick J . Wong" <[email protected]>,
"Martin K . Petersen" <[email protected]>,
Jonathan Corbet <[email protected]>,
"[email protected]" <[email protected]>,
"[email protected]" <[email protected]>,
"[email protected]" <[email protected]>,
"[email protected]" <[email protected]>,
"[email protected]" <[email protected]>,
"[email protected]" <[email protected]>,
"[email protected]" <[email protected]>
Subject: RE: [PATCH v1 2/6] iov_iter: optimise bvec iov_iter_advance()
Date: Tue, 15 Dec 2020 09:37:53 +0000 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <5c9c22dbeecad883ca29b31896c262a8d2a77132.1607976425.git.asml.silence@gmail.com>
From: Pavel Begunkov
> Sent: 15 December 2020 00:20
>
> iov_iter_advance() is heavily used, but implemented through generic
> iteration. As bvecs have a specifically crafted advance() function, i.e.
> bvec_iter_advance(), which is faster and slimmer, use it instead.
>
> Signed-off-by: Pavel Begunkov <[email protected]>
> ---
> lib/iov_iter.c | 19 +++++++++++++++++++
> 1 file changed, 19 insertions(+)
>
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index 1635111c5bd2..5b186dc2c9ea 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -1067,6 +1067,21 @@ static void pipe_advance(struct iov_iter *i, size_t size)
> pipe_truncate(i);
> }
>
> +static void iov_iter_bvec_advance(struct iov_iter *i, size_t size)
> +{
> + struct bvec_iter bi;
> +
> + bi.bi_size = i->count;
> + bi.bi_bvec_done = i->iov_offset;
> + bi.bi_idx = 0;
> + bvec_iter_advance(i->bvec, &bi, size);
> +
> + i->bvec += bi.bi_idx;
> + i->nr_segs -= bi.bi_idx;
> + i->count = bi.bi_size;
> + i->iov_offset = bi.bi_bvec_done;
> +}
> +
> void iov_iter_advance(struct iov_iter *i, size_t size)
> {
> if (unlikely(iov_iter_is_pipe(i))) {
> @@ -1077,6 +1092,10 @@ void iov_iter_advance(struct iov_iter *i, size_t size)
> i->count -= size;
> return;
> }
> + if (iov_iter_is_bvec(i)) {
> + iov_iter_bvec_advance(i, size);
> + return;
> + }
> iterate_and_advance(i, size, v, 0, 0, 0)
> }
This seems to add yet another comparison before what is probably
the common case on an IOVEC (ie normal userspace buffer).
Can't the call to bver_iter_advance be dropped into the 'advance'
path for BVEC's inside iterate_and_advance?
iterate_and_advance itself has three 'unlikely' conditional tests
that may be mis-predicted taken before the 'likely' path.
One is for DISCARD which is checked twice on the object I just
looked at - the test in iov_iter_advance() is pointless.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2020-12-15 9:43 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-15 0:20 [PATCH v1 0/6] no-copy bvec Pavel Begunkov
2020-12-15 0:20 ` [PATCH v1 1/6] target/file: allocate the bvec array as part of struct target_core_file_cmd Pavel Begunkov
2020-12-15 0:20 ` [PATCH v1 2/6] iov_iter: optimise bvec iov_iter_advance() Pavel Begunkov
2020-12-15 9:37 ` David Laight [this message]
2020-12-15 11:23 ` Pavel Begunkov
2020-12-15 13:54 ` David Laight
2020-12-15 13:56 ` Pavel Begunkov
2020-12-22 14:03 ` Christoph Hellwig
2020-12-15 0:20 ` [PATCH v1 3/6] bio: deduplicate adding a page into bio Pavel Begunkov
2020-12-22 14:04 ` Christoph Hellwig
2020-12-15 0:20 ` [PATCH v1 4/6] block/psi: remove PSI annotations from direct IO Pavel Begunkov
2020-12-15 0:56 ` Dave Chinner
2020-12-15 1:03 ` Pavel Begunkov
2020-12-15 1:33 ` Dave Chinner
2020-12-15 11:41 ` Pavel Begunkov
2020-12-22 14:07 ` Christoph Hellwig
2020-12-15 0:20 ` [PATCH v1 5/6] bio: add a helper calculating nr segments to alloc Pavel Begunkov
2020-12-15 1:00 ` Dave Chinner
2020-12-15 1:07 ` Pavel Begunkov
2020-12-15 1:09 ` Dave Chinner
2020-12-22 14:07 ` Christoph Hellwig
2020-12-15 0:20 ` [PATCH v1 6/6] block/iomap: don't copy bvec for direct IO Pavel Begunkov
2020-12-15 1:09 ` Dave Chinner
2020-12-15 1:15 ` Pavel Begunkov
2020-12-22 14:15 ` Christoph Hellwig
2020-12-15 1:41 ` [PATCH v1 0/6] no-copy bvec Ming Lei
2020-12-15 11:14 ` Pavel Begunkov
2020-12-15 12:03 ` Ming Lei
2020-12-15 14:05 ` Pavel Begunkov
2020-12-22 14:11 ` Christoph Hellwig
2020-12-23 12:52 ` Pavel Begunkov
2020-12-23 15:51 ` Christoph Hellwig
2020-12-23 16:04 ` James Bottomley
2020-12-23 20:23 ` Douglas Gilbert
2020-12-23 20:32 ` Pavel Begunkov
2020-12-24 6:41 ` Christoph Hellwig
2020-12-24 16:45 ` Douglas Gilbert
2020-12-24 17:30 ` James Bottomley
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