From: Jens Axboe <axboe@kernel.dk>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Pavel Begunkov <asml.silence@gmail.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [git pull] iov_iter fixes
Date: Fri, 10 Sep 2021 09:08:02 -0600 [thread overview]
Message-ID: <75caf6d6-26d4-7146-c497-ed89b713d878@kernel.dk> (raw)
In-Reply-To: <YTtu1V1c1emiYII9@zeniv-ca.linux.org.uk>
On 9/10/21 8:42 AM, Al Viro wrote:
> On Fri, Sep 10, 2021 at 07:57:49AM -0600, Jens Axboe wrote:
>
>> It was just a quick hack, might very well be too eager to go through
>> those motions. But pondering this instead of sleeping, we don't need to
>> copy all of iov_iter in order to restore the state, and we can use the
>> same advance after restoring. So something like this may be more
>> palatable. Caveat - again untested, and I haven't tested the performance
>> impact of this at all.
>
> You actually can cut it down even more - nr_segs + iov remains constant
> all along, so you could get away with just 3 words here... I would be
Mmm, the iov pointer remains constant? Maybe I'm missing your point, but
the various advance functions are quite happy to increment iter->iov or
iter->bvec, so we need to restore them. From a quick look, looks like
iter->nr_segs is modified for advancing too.
What am I missing?
> surprised if extra memory traffic had shown up - it's well within the
> noise from register spills, (un)inlining, etc. We are talking about
> 3 (or 4, with your variant) extra words on one stack frame (and that'd
> be further offset by removal of ->truncated); I'd still like to see the
> profiling data, but concerns about extra memory traffic due to that
> are, IMO, misplaced.
See other email that was just sent out, it is measurable but pretty
minimal. But that's also down to about 1/3rd of copying the whole
thing blindly, so definitely a better case.
--
Jens Axboe
next prev parent reply other threads:[~2021-09-10 15:08 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-09 4:22 [git pull] iov_iter fixes Al Viro
2021-09-09 19:37 ` Linus Torvalds
2021-09-09 21:19 ` Jens Axboe
2021-09-09 21:39 ` Jens Axboe
2021-09-09 21:56 ` Linus Torvalds
2021-09-09 22:21 ` Jens Axboe
2021-09-09 22:56 ` Linus Torvalds
2021-09-10 1:35 ` Jens Axboe
2021-09-10 2:43 ` Jens Axboe
2021-09-10 2:48 ` Al Viro
2021-09-10 3:06 ` Jens Axboe
2021-09-10 3:15 ` Al Viro
2021-09-10 3:23 ` Jens Axboe
2021-09-10 3:24 ` Al Viro
2021-09-10 3:28 ` Jens Axboe
2021-09-13 15:29 ` David Laight
2021-09-09 21:42 ` Dave Chinner
2021-09-10 2:57 ` Al Viro
2021-09-10 3:05 ` Jens Axboe
2021-09-10 3:11 ` Al Viro
2021-09-10 3:22 ` Jens Axboe
2021-09-10 3:27 ` Al Viro
2021-09-10 3:30 ` Jens Axboe
2021-09-10 3:36 ` Al Viro
2021-09-10 13:57 ` Jens Axboe
2021-09-10 14:42 ` Al Viro
2021-09-10 15:08 ` Jens Axboe [this message]
2021-09-10 15:32 ` Al Viro
2021-09-10 15:36 ` Jens Axboe
2021-09-10 15:04 ` Jens Axboe
2021-09-10 16:06 ` Jens Axboe
2021-09-10 16:44 ` Linus Torvalds
2021-09-10 16:56 ` Al Viro
2021-09-10 16:58 ` Linus Torvalds
2021-09-10 17:26 ` Jens Axboe
2021-09-10 17:31 ` Linus Torvalds
2021-09-10 17:32 ` Jens Axboe
2021-09-10 18:48 ` Al Viro
2021-09-10 19:04 ` Linus Torvalds
2021-09-10 19:10 ` Linus Torvalds
2021-09-10 19:10 ` Jens Axboe
2021-09-10 17:04 ` Jens Axboe
2021-09-09 22:54 ` Pavel Begunkov
2021-09-09 22:57 ` Pavel Begunkov
2021-09-09 23:14 ` Pavel Begunkov
2021-09-09 20:03 ` pr-tracker-bot
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