[46743] in North American Network Operators' Group
fixing TCP buffers (Re: packet reordering at exchange points)
daemon@ATHENA.MIT.EDU (E.B. Dreger)
Tue Apr 9 18:51:53 2002
Date: Tue, 9 Apr 2002 22:51:27 +0000 (GMT)
From: "E.B. Dreger" <eddy+public+spam@noc.everquick.net>
To: Richard A Steenbergen <ras@e-gerbil.net>
Cc: Paul Vixie <paul@vix.com>, nanog@merit.edu
In-Reply-To: <20020409200353.GU523@overlord.e-gerbil.net>
Message-ID: <Pine.LNX.4.20.0204092102060.20028-100000@www.everquick.net>
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Errors-To: owner-nanog-outgoing@merit.edu
> Date: Tue, 9 Apr 2002 16:03:53 -0400
> From: Richard A Steenbergen <ras@e-gerbil.net>
> To transfer 1Gb/s across 100ms I need to be prepared to buffer at least
> 25MB of data. According to pricewatch, I can pick up a high density 512MB
[ snip ]
> The problem isn't the lack of hardware, it's a lack of good software (both
[ snip ]
But how many simultaneous connections? Until TCP stacks start
using window autotuning (of which I know you're well aware), we
must either use suboptimal windows or chew up ridiculous amounts
of memory. Yes, bad software, but still a limit...
It would be nice to allocate a 32MB chunk of RAM for buffers,
then dynamically split it between streams. Fragmentation makes
that pretty much impossible.
OTOH... perhaps that's a reasonable start:
1. Alloc buffer of size X
2. Let it be used for Y streams
3. When we have Y streams, split each stream "sub-buffer" into Y
parts, giving capacity for Y^2, streams.
Aggregate transmission can't exceed line rate. So instead of
fixed-size buffers for each stream, perhaps our TOTAL buffer size
should remain constant.
Use PSC-style autotuning to eek out more capacity/performance,
instead of using fixed value of "Y" or splitting each and every
last buffer. (Actually, I need to reread/reexamine the PSC code
in case it actually _does_ use a fixed total buffer size.)
This shouldn't be terribly hard to hack into an IP stack...
--
Eddy
Brotsman & Dreger, Inc. - EverQuick Internet Division
Phone: +1 (316) 794-8922 Wichita/(Inter)national
Phone: +1 (785) 865-5885 Lawrence
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