[Beowulf] Performance tuning for Jumbo Frames

[Alex Chekholko]

On Tue, 15 Dec 2009 13:22:56 -0800
Greg Lindahl <lindahl at pbm.com> wrote:

> On Tue, Dec 15, 2009 at 12:49:23PM -0500, Scott Atchley wrote:
> 
> > You can test it by using the size parameter with ping:
> >
> > $ ping -s <size_in_bytes> <host>
> >
> > If they all drop, then you have exceeded the MTU of some device.
> 
> [lindahl at greg-desk b]$ ping -s 60000 rich-desk
> PING rich-desk (64.13.159.69) 60000(60028) bytes of data.
> 60008 bytes from rich-desk (64.13.159.69): icmp_seq=1 ttl=64 time=1.36 ms
> 60008 bytes from rich-desk (64.13.159.69): icmp_seq=2 ttl=64 time=1.32 ms
> 
> I never knew I bought such advanced network gear!

Not sure if you're joking, but yes, you also have to tell ping to set
the "don't fragment" bit.

So on Ubuntu 9.04 it would be:

ping -M do -s SIZE whatever.host.com

Regards,
-- 
Alex Chekholko   chekh at pcbi.upenn.edu