From: Pavel Begunkov <asml.silence@gmail.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] iov_iter: optimise bvec iov_iter_advance()
Date: Thu, 3 Dec 2020 11:48:56 +0000 [thread overview]
Message-ID: <eb02fa7f-956e-ce7e-6a56-82318b2c6d2e@gmail.com> (raw)
In-Reply-To: <20201203091406.GA6189@infradead.org>
On 03/12/2020 09:14, Christoph Hellwig wrote:
>> @@ -1077,6 +1077,20 @@ void iov_iter_advance(struct iov_iter *i, size_t size)
>> i->count -= size;
>> return;
>> }
>> + if (iov_iter_is_bvec(i)) {
>> + 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;
>> + return;
>> + }
>> iterate_and_advance(i, size, v, 0, 0, 0)
>
> I like the idea, but whu not avoid the on-stack bvec_iter and just
> open code this entirely using a new helper? E.g.
It's inlined and the on-stack iter is completely optimised out. Frankly,
I'd rather not open-code bvec_iter_advance(), at least for this chunk to
be findable from bvec.h, e.g. grep bvec_iter and bvec_for_each. Though,
I don't like myself that preamble/postamble.
>
> static void bio_iov_iter_advance(struct iov_iter *i, size_t bytes)
> {
> unsigned int cnt;
>
> i->count -= bytes;
>
> bytes += i->iov_offset;
> for (cnt = 0; bytes && bytes >= i->bvec[cnt].bv_len; cnt++)
> bytes -= i->bvec[cnt].bv_len;
> i->iov_offset = bytes;
>
> i->bvec += cnt;
> i->nr_segs -= cnt;
> }
>
--
Pavel Begunkov
next prev parent reply other threads:[~2020-12-03 11:53 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-03 1:45 [PATCH] iov_iter: optimise bvec iov_iter_advance() Pavel Begunkov
2020-12-03 9:14 ` Christoph Hellwig
2020-12-03 11:48 ` Pavel Begunkov [this message]
2020-12-09 8:33 ` Christoph Hellwig
2020-12-09 12:06 ` Pavel Begunkov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=eb02fa7f-956e-ce7e-6a56-82318b2c6d2e@gmail.com \
--to=asml.silence@gmail.com \
--cc=hch@infradead.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).