[Beowulf] RHEL5 network throughput/scalability

Perry E. Metzger perry at piermont.com
Fri Jun 13 19:21:05 PDT 2008

A number of these seem rather odd, or unrelated to performance.

Walid <walid.shaari at gmail.com> writes:
> It is lame, however i managed to get the following kernel paramter to scale
> well in terms of both performance per node, and scalability over  a high
> bandwidth low latency network
> net.ipv4.tcp_workaround_signed_windows = 1

This is a workaround for a buggy remote TCP. If you have a homogeneous
network of linux boxes, it will have no effect.

> net.ipv4.tcp_congestion_control = vegas

I'm under the impression that the Vegas congestion control policy is
not well loved by the experts on TCP performance.

> net.ipv4.route.max_size = 8388608

This sets the size of the routing cache. You've set it to a rather
large and fairly random number.

> net.ipv4.icmp_ignore_bogus_error_responses = 0
> net.ipv4.icmp_echo_ignore_broadcasts = 0

Why would paying attention to bogus ICMPs and to ICMP broadcasts help
performance? Neither should be prevalent enough to make any
difference, and one would naively expect performance to be improved by
ignoring such things, not by paying attention to them...

> net.ipv4.tcp_max_orphans = 262144

I'm not clear on why this would help unless you were expecting really
massive numbers of unattached sockets -- also you're saying that up to
16M of kernel memory can be used for this purpose...

> net.core.netdev_max_backlog = 2000

This implies your processes are going to get massive numbers of TCP
connections per unit time. Are they? It is certainly not a *general*
performance improvement...


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