> From: Jayson Nordwick <[EMAIL PROTECTED]>
> Date: 1999-09-08 17:38:56 -0700
> To: [EMAIL PROTECTED]
> Subject: message queues for I/O (usenix paper)
> Content-id: <[EMAIL PROTECTED]>
> Delivered-to: [EMAIL PROTECTED]
> X-Loop: FreeBSD.ORG
>
> There is alot of talk going on over at the linux-kernel mailing list
> about implementing synchronous messaging for I/O. They are
talking about
> a paper that was presented at USENIX:
>
> http://www.cs.rice.edu/~gaurav/papers/usenix99.ps
>
> The general idea is that select() and poll() fall over with large
numbers of
> file descriptors for two reasons. First, scanning the interest
list begins to
> consume more time. Second, the stateless nature between calls
means that
> alot of redundant processing occurs. The solution these guys (the
authors)
> say is to have a way of registering interest in descriptors, then
you can
> call a procedure to find out what has changed since last time.
>
> I personally think that select() is just fine and can be implemented
> more efficiently than currently, but I would be willing to give it
a shot
> at both cooperating with the Linux people to get a good Linux/FreeBSD
> API layed down and then implementing it.
>
> I know some of you heard this paper presented so does anybody have any
> ideas about it?
>
> Does anybody care?
>From the FWIW department, we have, in the Darwin source, an
implementation of a "select replacement" that is designed to get
around some of the (perceived or real) issues with select(), e.g.,
looking at a long (FD_SETSIZE or larger) array of bits several times
in the kernel and in user space.
In the available sources, this is represented in sys/ev.h, and is
implemented only for sockets. Our tests indicate a roughly 5-10%
speed improvement when a lot of sockets are in use but not
exuberantly so.
For Darwin in the future (the Core OS for Mac OS X), this scheme
will be somewhat generalized, to provide a uniform mechanism for
fielding events from any subsystem. It will be made more interesting
by the need to incorporate mach message handling in addition to
file-descriptor-based events.
Have a look, should this be of interest. I'll be happy to field
questions, since the doc is a bit, oh, scant...
Regards,
Justin
--
Justin C. Walker, Curmudgeon-At-Large *
Institute for General Semantics |
Manager, CoreOS Networking | When crypto is outlawed,
Apple Computer, Inc. | Only outlaws will have crypto.
2 Infinite Loop |
Cupertino, CA 95014 |
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