From: Al Viro <viro@zeniv.linux.org.uk>
To: Jens Axboe <axboe@kernel.dk>
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 03:11:19 +0000 [thread overview]
Message-ID: <YTrM130S32ymVhXT@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <b8786a7e-5616-ce83-c2f2-53a4754bf5a4@kernel.dk>
On Thu, Sep 09, 2021 at 09:05:13PM -0600, Jens Axboe wrote:
> On 9/9/21 8:57 PM, Al Viro wrote:
> > On Thu, Sep 09, 2021 at 03:19:56PM -0600, Jens Axboe wrote:
> >
> >> Not sure how we'd do that, outside of stupid tricks like copy the
> >> iov_iter before we pass it down. But that's obviously not going to be
> >> very efficient. Hence we're left with having some way to reset/reexpand,
> >> even in the presence of someone having done truncate on it.
> >
> > "Obviously" why, exactly? It's not that large a structure; it's not
> > the optimal variant, but I'd like to see profiling data before assuming
> > that it'll cause noticable slowdowns.
>
> It's 48 bytes, and we have to do it upfront. That means we'd be doing it
> for _all_ requests, not just when we need to retry. As an example, current
> benchmarks are at ~4M read requests per core. That'd add ~200MB/sec of
> memory traffic just doing this copy.
Umm... How much of that will be handled by cache?
> Besides, I think that's moot as there's a better way.
I hope so, but I'm afraid that "let's reload from userland on e.g. short
reads" is not better - there's a plenty of interesting corner cases you
need to handle with that.
next prev parent reply other threads:[~2021-09-10 3:13 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 [this message]
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
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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