charmm scalability on 2.4 kernels

Josip Loncaric josip at
Tue Jan 8 07:41:06 PST 2002

"Eray Ozkural (exa)" wrote:
> It was said before on this list that 2.4 already incorporates TCP fixes. Has
> anybody met a similar situation before?

Actually, Linux kernel 2.4 incorporates an improved yet very different
TCP stack where my TCP fixes do not help much in my usual test case
(point-to-point streaming of small messages).  However, Steve's
scalability problems with the stock 2.4 TCP are very interesting, since
they involve many machines, i.e. a completely different communication
pattern from my usual point-to-point tests.

Old 2.2+fix combination was pretty efficient at aggregating small
messages into larger TCP packets before sending, in fact better than
stock 2.4.  Packet aggregation is something that depends on delicate
timing of congestion control events on both sender and receiver; this is
very sensitive to the application's communication pattern.  Perhaps a
2.4 TCP fix would need to be developed after all...


Dr. Josip Loncaric, Research Fellow               mailto:josip at
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