From: Derek Martin <[EMAIL PROTECTED]>
Subject: Re: Linux 20k Socket Challenge
> > Basically, it revolves around the Linux kernel, and adding the
> > capability for a very large number of simo IP connections. We need to
> > be able to have a linux box support up to and hopefully over 20k simo
> > TCP connections.
> Just out of curiosity, what on earth for?
Instant messaging. This situation lends itself more twards many, little
used sockets, then using UDP. And the overhead of TCP, while reducing
buffer size, is less then or equal to that of an application transfering
fairly large packets via UDP.
> Well, I have no idea if this will be useful, but...
> There's a socket option for the buffer size... But by reducing it you
> could run into performance issues. The options are SO_SNDBUF and
> SO_RCVBUF. See the socket(7) man page for details.
> Be aware that when you call setsockopt(2) with the buffer size, the Linux
> kernel will likely set the size to 2 x the specified size. Why it does
> this, I have no idea. To check the buffer sizes, use getsockopt(2) with
> the same socket options.
> Incidentally, the man page also reveals that the default (system-wide)
> value for the buffer is set by the wmem_default sysctl, so you could set
> that.
Yep, after more investigation, that's what we discovered. The system wide
setting is the one we wanted. We're not concerned with the performance
isues, becouse these are little used sockets. When I say little used, they
are used regularly, but nor for transfering 'much' data. Coupla K a minute
perhaps.. After further reading, I actually learned quite a deal regarding
buffer wise, and dynamic sizing of buffer windows.. The only thing lacking
is a dynamic shrinking of the buffers.. The other interesting thing we
found is, many Linux distros ship their wmem_default and rmem_default at
32k. Redhat ships them at 64k.. ;-P
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