From: Jamie Lokier <jamie@shareable.org>
To: Davide Libenzi <davidel@xmailserver.org>
Cc: "David S. Miller" <davem@redhat.com>,
Eric Varsanyi <e0206@foo21.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
kuznet@ms2.inr.ac.ru
Subject: Re: POLLRDONCE optimisation for epoll users (was: epoll and half closed TCP connections)
Date: Mon, 14 Jul 2003 04:42:44 +0100 [thread overview]
Message-ID: <20030714034244.GC23534@mail.jlokier.co.uk> (raw)
In-Reply-To: <Pine.LNX.4.55.0307132018200.15022@bigblue.dev.mcafeelabs.com>
Davide Libenzi wrote:
> > > > (a) fd isn't a socket
> > > > (b) fd isn't a TCP socket
> > > > (c) kernel version <= 2.5.75
> > > > (d) SO_RCVLOWAT < s
> > > > (e) there is urgent data with OOBINLINE (I think)
> >
> > > Jamie, did you smoke that stuff again ? :)
> > > With Eric patch in the proper places it is just fine. You just make
> > > f_op->poll() to report the extra flag other that POLLIN. What's the problem ?
> >
> > The problem in cases (a)-(e) is your loop will call read() just once
> > when it needs to call read() until it sees EAGAIN.
> >
> > What's wrong is the behaviour of your program when the extra flag
> > _isn't_ set.
>
> Jamie, the loop will call read(2) until data is available. With the trick
> of checking the returned number of bytes you can avoid the extra EAGAIN
> read(2). That's the point of the read(2) trick.
That _only_ works if none of those conditions (a)-(e) applies.
Otherwise, short reads are possible when there is more to come.
Sure, if you're willing to assert that the program is running on
kernel >= 2.5.76, all its fds are for sure TCP sockets and you added
the POLLPRI check, then yes it's fine.
I think mine is better because it works always, and you are free to
code the optimisation in any programs, libraries etc.
> The final check for RDHUP will tell that it has no more to wait for
> POLLINs since there's no more someone sending.
Sure, _that_ check is fine.
-- Jamie
next prev parent reply other threads:[~2003-07-14 3:28 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-07-12 18:16 [Patch][RFC] epoll and half closed TCP connections Eric Varsanyi
2003-07-12 19:44 ` Jamie Lokier
2003-07-12 20:51 ` Eric Varsanyi
2003-07-12 20:48 ` Davide Libenzi
2003-07-12 21:19 ` Eric Varsanyi
2003-07-12 21:20 ` Davide Libenzi
2003-07-12 21:41 ` Davide Libenzi
2003-07-12 23:11 ` Eric Varsanyi
2003-07-12 23:55 ` Davide Libenzi
2003-07-13 1:05 ` Eric Varsanyi
2003-07-13 20:32 ` David Schwartz
2003-07-13 21:10 ` Jamie Lokier
2003-07-13 23:05 ` David Schwartz
2003-07-13 23:09 ` Davide Libenzi
2003-07-14 8:14 ` Alan Cox
2003-07-14 15:03 ` Davide Libenzi
2003-07-14 1:27 ` Jamie Lokier
2003-07-13 21:14 ` Davide Libenzi
2003-07-13 23:05 ` David Schwartz
2003-07-13 23:11 ` Davide Libenzi
2003-07-13 23:52 ` Entrope
2003-07-14 6:14 ` David Schwartz
2003-07-14 7:20 ` Jamie Lokier
2003-07-14 1:51 ` Jamie Lokier
2003-07-14 6:14 ` David Schwartz
2003-07-15 20:27 ` James Antill
2003-07-16 1:46 ` David Schwartz
2003-07-16 2:09 ` James Antill
2003-07-13 13:12 ` Jamie Lokier
2003-07-13 16:55 ` Davide Libenzi
2003-07-12 20:01 ` Davide Libenzi
2003-07-13 5:24 ` David S. Miller
2003-07-13 14:07 ` Jamie Lokier
2003-07-13 17:00 ` Davide Libenzi
2003-07-13 19:15 ` Jamie Lokier
2003-07-13 23:03 ` Davide Libenzi
2003-07-14 1:41 ` Jamie Lokier
2003-07-14 2:24 ` POLLRDONCE optimisation for epoll users (was: epoll and half closed TCP connections) Jamie Lokier
2003-07-14 2:37 ` Davide Libenzi
2003-07-14 2:43 ` Davide Libenzi
2003-07-14 2:56 ` Jamie Lokier
2003-07-14 3:02 ` Davide Libenzi
2003-07-14 3:16 ` Jamie Lokier
2003-07-14 3:21 ` Davide Libenzi
2003-07-14 3:42 ` Jamie Lokier [this message]
2003-07-14 4:00 ` Davide Libenzi
2003-07-14 5:51 ` Jamie Lokier
2003-07-14 6:24 ` Davide Libenzi
2003-07-14 6:57 ` Jamie Lokier
2003-07-14 3:12 ` Jamie Lokier
2003-07-14 3:17 ` Davide Libenzi
2003-07-14 3:35 ` Jamie Lokier
2003-07-14 3:04 ` Jamie Lokier
2003-07-14 3:12 ` Davide Libenzi
2003-07-14 3:27 ` Jamie Lokier
2003-07-14 17:09 ` [Patch][RFC] epoll and half closed TCP connections kuznet
2003-07-14 17:09 ` Davide Libenzi
2003-07-14 21:45 ` Jamie Lokier
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=20030714034244.GC23534@mail.jlokier.co.uk \
--to=jamie@shareable.org \
--cc=davem@redhat.com \
--cc=davidel@xmailserver.org \
--cc=e0206@foo21.com \
--cc=kuznet@ms2.inr.ac.ru \
--cc=linux-kernel@vger.kernel.org \
/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).