[Beowulf] Help with inconsistent network performance

Michael H. Frese Michael.Frese at NumerEx.com
Tue Dec 18 13:23:17 EST 2007


Brendan,

If you are doing this via nfs, you should be sure that mounts are 
done using the tcp parameter in /etc/fstab.  Otherwise you may get 
udp, and I have seen problems with that as recently as Fedora 8 this morning!


Mike

At 08:03 PM 12/17/2007, Brendan Moloney wrote:
>I have a cluster of 8 Linux machines connected with gigabit ethernet 
>(full duplex) to a HP Procurve 2848 switch.   I am using the 
>machines to do interactive distributed rendering.  I have noticed 
>that the final gather stage (where the intermediate images from the 
>render nodes are sent back to the viewing node) has "hiccups" in the 
>performance.  These hiccups occur with as few as two render nodes, 
>and become more common as I add more render nodes.  With a 512x512 
>image the final gather usually takes a few milliseconds for each 
>frame, but when the hiccups occur it is more like 200+ milliseconds.
>
>Since it is a full duplex switched network, there should not be any 
>collisions happening.  Since the image is less than 1 MB total, I 
>don't think I am saturating the switch.  I have checked the contents 
>of /sbin/ifconfig and there are zero erroneous packets being 
>reported.  At this point I am really at a loss as to what is causing 
>this.  Any input on things to check would be greatly appreciated.
>
>Thanks,
>Brendan
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