From: Linus Torvalds <torvalds@linux-foundation.org>
To: David Miller <davem@davemloft.net>
Cc: zach.brown@oracle.com, linux-kernel@vger.kernel.org,
linux-aio@kvack.org, suparna@in.ibm.com, bcrl@kvack.org,
mingo@elte.hu
Subject: Re: [PATCH 0 of 4] Generic AIO by scheduling stacks
Date: Sat, 10 Feb 2007 18:49:56 -0800 (PST) [thread overview]
Message-ID: <Pine.LNX.4.64.0702101841450.8424@woody.linux-foundation.org> (raw)
In-Reply-To: <20070210.165602.07642259.davem@davemloft.net>
On Sat, 10 Feb 2007, David Miller wrote:
>
> Even if you have everything, every page, every log file, in the page
> cache, everything talking over the network wants to block.
>
> Will you create a thread every time tcp_sendmsg() hits the send queue
> limits?
No. You use epoll() for those.
> The idea is probably excellent for operations on real files, but it's
> going to stink badly for networking stuff.
And I actually talked about that in one of the emails already. There is no
way you can beat an event-based thing for things that _are_ event-based.
That means mainly networking.
For things that aren't event-based, but based on real IO (ie filesystems
etc), event models *suck*. They suck because the code isn't amenable to it
in the first place (ie anybody who thinks that a filesystem is like a
network stack and can be done as a state machine with packets is just
crazy!).
So you would be crazy to makea web server that uses this to handle _all_
outstanding IO. Network connections are often slow, and you can have tens
of thousands outstanding (and some may be outstanding for hours until they
time out, if ever). But that's the whole point: you can easily mix the
two, as given in several examples already (ie you can easily make the main
loop itself basically do just
for (;;) {
async(epoll); /* wait for networking events */
async_wait(); /* wait for epoll _or_ any of the outstanding file IO events */
handle_completed_events();
}
and it's actually a lot better than an event model, exactly because now
you can handle events _and_ non-events well (a pure event model requires
that _everything_ be an event, which works fine for some things, but works
really badly for other things).
There's a reason why a lot of UNIX system calls are blocking: they just
don't make sense as event models, because there is no sensible half-way
point that you can keep track of (filename lookup is the most common
example).
Linus
next prev parent reply other threads:[~2007-02-11 2:50 UTC|newest]
Thread overview: 151+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-01-30 20:39 [PATCH 0 of 4] Generic AIO by scheduling stacks Zach Brown
2007-01-30 20:39 ` [PATCH 1 of 4] Introduce per_call_chain() Zach Brown
2007-01-30 20:39 ` [PATCH 2 of 4] Introduce i386 fibril scheduling Zach Brown
2007-02-01 8:36 ` Ingo Molnar
2007-02-01 13:02 ` Ingo Molnar
2007-02-01 13:19 ` Christoph Hellwig
2007-02-01 13:52 ` Ingo Molnar
2007-02-01 17:13 ` Mark Lord
2007-02-01 18:02 ` Ingo Molnar
2007-02-02 13:23 ` Andi Kleen
2007-02-01 21:52 ` Zach Brown
2007-02-01 22:23 ` Benjamin LaHaise
2007-02-01 22:37 ` Zach Brown
2007-02-02 13:22 ` Andi Kleen
2007-02-01 20:07 ` Linus Torvalds
2007-02-02 10:49 ` Ingo Molnar
2007-02-02 15:56 ` Linus Torvalds
2007-02-02 19:59 ` Alan
2007-02-02 20:14 ` Linus Torvalds
2007-02-02 20:58 ` Davide Libenzi
2007-02-02 21:09 ` Linus Torvalds
2007-02-02 21:30 ` Alan
2007-02-02 21:30 ` Linus Torvalds
2007-02-02 22:42 ` Ingo Molnar
2007-02-02 23:01 ` Linus Torvalds
2007-02-02 23:17 ` Linus Torvalds
2007-02-03 0:04 ` Alan
2007-02-03 0:23 ` bert hubert
2007-02-02 22:48 ` Alan
2007-02-05 16:44 ` Zach Brown
2007-02-02 22:21 ` Ingo Molnar
2007-02-02 22:49 ` Linus Torvalds
2007-02-02 23:55 ` Ingo Molnar
2007-02-03 0:56 ` Linus Torvalds
2007-02-03 7:15 ` Suparna Bhattacharya
2007-02-03 8:23 ` Ingo Molnar
2007-02-03 9:25 ` Matt Mackall
2007-02-03 10:03 ` Ingo Molnar
2007-02-05 17:44 ` Zach Brown
2007-02-05 19:26 ` Davide Libenzi
2007-02-05 19:41 ` Zach Brown
2007-02-05 20:10 ` Davide Libenzi
2007-02-05 20:21 ` Zach Brown
2007-02-05 20:42 ` Linus Torvalds
2007-02-05 20:39 ` Linus Torvalds
2007-02-05 21:09 ` Davide Libenzi
2007-02-05 21:31 ` Kent Overstreet
2007-02-06 20:25 ` Davide Libenzi
2007-02-06 20:46 ` Linus Torvalds
2007-02-06 21:16 ` David Miller
2007-02-06 21:28 ` Linus Torvalds
2007-02-06 21:31 ` David Miller
2007-02-06 21:46 ` Eric Dumazet
2007-02-06 21:50 ` Linus Torvalds
2007-02-06 22:28 ` Zach Brown
2007-02-06 22:45 ` Kent Overstreet
2007-02-06 23:04 ` Linus Torvalds
2007-02-07 1:22 ` Kent Overstreet
2007-02-06 23:23 ` Davide Libenzi
2007-02-06 23:39 ` Joel Becker
2007-02-06 23:56 ` Davide Libenzi
2007-02-07 0:06 ` Joel Becker
2007-02-07 0:23 ` Davide Libenzi
2007-02-07 0:44 ` Joel Becker
2007-02-07 1:15 ` Davide Libenzi
2007-02-07 1:24 ` Kent Overstreet
2007-02-07 1:30 ` Joel Becker
2007-02-07 6:16 ` Michael K. Edwards
2007-02-07 9:17 ` Michael K. Edwards
2007-02-07 9:37 ` Michael K. Edwards
2007-02-06 0:32 ` Davide Libenzi
2007-02-05 21:21 ` Zach Brown
2007-02-02 23:37 ` Davide Libenzi
2007-02-03 0:02 ` Davide Libenzi
2007-02-05 17:12 ` Zach Brown
2007-02-05 18:24 ` Davide Libenzi
2007-02-05 21:44 ` David Miller
2007-02-06 0:15 ` Davide Libenzi
2007-02-05 21:36 ` bert hubert
2007-02-05 21:57 ` Linus Torvalds
2007-02-05 22:07 ` bert hubert
2007-02-05 22:15 ` Zach Brown
2007-02-05 22:34 ` Davide Libenzi
2007-02-06 0:27 ` Scot McKinley
2007-02-06 0:48 ` David Miller
2007-02-06 0:48 ` Joel Becker
2007-02-05 17:02 ` Zach Brown
2007-02-05 18:52 ` Davide Libenzi
2007-02-05 19:20 ` Zach Brown
2007-02-05 19:38 ` Davide Libenzi
2007-02-04 5:12 ` Davide Libenzi
2007-02-05 17:54 ` Zach Brown
2007-01-30 20:39 ` [PATCH 3 of 4] Teach paths to wake a specific void * target instead of a whole task_struct Zach Brown
2007-01-30 20:39 ` [PATCH 4 of 4] Introduce aio system call submission and completion system calls Zach Brown
2007-01-31 8:58 ` Andi Kleen
2007-01-31 17:15 ` Zach Brown
2007-01-31 17:21 ` Andi Kleen
2007-01-31 19:23 ` Zach Brown
2007-02-01 11:13 ` Suparna Bhattacharya
2007-02-01 19:50 ` Trond Myklebust
2007-02-02 7:19 ` Suparna Bhattacharya
2007-02-02 7:45 ` Andi Kleen
2007-02-01 22:18 ` Zach Brown
2007-02-02 3:35 ` Suparna Bhattacharya
2007-02-01 20:26 ` bert hubert
2007-02-01 21:29 ` Zach Brown
2007-02-02 7:12 ` bert hubert
2007-02-04 5:12 ` Davide Libenzi
2007-01-30 21:58 ` [PATCH 0 of 4] Generic AIO by scheduling stacks Linus Torvalds
2007-01-30 22:23 ` Linus Torvalds
2007-01-30 22:53 ` Zach Brown
2007-01-30 22:40 ` Zach Brown
2007-01-30 22:53 ` Linus Torvalds
2007-01-30 23:45 ` Zach Brown
2007-01-31 2:07 ` Benjamin Herrenschmidt
2007-01-31 2:04 ` Benjamin Herrenschmidt
2007-01-31 2:46 ` Linus Torvalds
2007-01-31 3:02 ` Linus Torvalds
2007-01-31 10:50 ` Xavier Bestel
2007-01-31 19:28 ` Zach Brown
2007-01-31 17:59 ` Zach Brown
2007-01-31 5:16 ` Benjamin Herrenschmidt
2007-01-31 5:36 ` Nick Piggin
2007-01-31 5:51 ` Nick Piggin
2007-01-31 6:06 ` Linus Torvalds
2007-01-31 8:43 ` Ingo Molnar
2007-01-31 20:13 ` Joel Becker
2007-01-31 18:20 ` Zach Brown
2007-01-31 17:47 ` Zach Brown
2007-01-31 17:38 ` Zach Brown
2007-01-31 17:51 ` Benjamin LaHaise
2007-01-31 19:25 ` Zach Brown
2007-01-31 20:05 ` Benjamin LaHaise
2007-01-31 20:41 ` Zach Brown
2007-02-04 5:13 ` Davide Libenzi
2007-02-04 20:00 ` Davide Libenzi
2007-02-09 22:33 ` Linus Torvalds
2007-02-09 23:11 ` Davide Libenzi
2007-02-09 23:35 ` Linus Torvalds
2007-02-10 18:45 ` Davide Libenzi
2007-02-10 19:01 ` Linus Torvalds
2007-02-10 19:35 ` Linus Torvalds
2007-02-10 20:59 ` Davide Libenzi
2007-02-10 0:04 ` Eric Dumazet
2007-02-10 0:12 ` Linus Torvalds
2007-02-10 0:34 ` Alan
2007-02-10 10:47 ` bert hubert
2007-02-10 18:19 ` Davide Libenzi
2007-02-11 0:56 ` David Miller
2007-02-11 2:49 ` Linus Torvalds [this message]
2007-02-14 16:42 ` James Antill
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