[Beowulf] Help with inconsistent network performance

Mark Hahn hahn at mcmaster.ca
Tue Dec 18 09:08:48 PST 2007

> final gather stage (where the intermediate images from the render nodes are
> sent back to the viewing node) has "hiccups" in the performance.  These

as perceived how?  do you mean your gather/gui machine pauses?  could it 
be as simple as allocating memory?  (if you do a significant memory
allocation under linux, the memory will be virtual until its written,
at which time pages will be allocated.  those allocations can trigger
frantic scavenging of memory by the kernel, and this can certainly 
interfere with, for instance, networking, especially at the user level.)

simply pre-zeroing the frames might make the problem go away.

if you really have some reason to blame the network, I'd go brute-force
and run tcpdump on all nodes to catch a hiccup, and see what's happening.

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