[Beowulf] Performance tuning for Jumbo Frames

[Eric W. Biederman]

Greg Lindahl <lindahl at pbm.com> writes:

> On Tue, Dec 15, 2009 at 11:41:59PM -0500, Patrick Geoffray wrote:
>
>> So, instead of requiring ~4K per port minimum, you need about ~20K per  
>> port. Add to that up to 8 priorities with DCB and the buffering  
>> requirement are quickly getting out of hand.
>
> Don't worry, switch vendors will simply implement it all poorly, just
> like InfiniBand. That's what always happens with overly-complicated
> QOS schemes.

The way I have heard per priority flow control expected to be used is
one priority does pause frames ( for fcoe ) and the other priorities
drop frames, as dropping frames when congested avoids head of line
blocking, and thus gives better network performance overall.

Of course in practice at 10G type speeds you want enough switch
buffers so you don't normally drop packets, but that is a different
story.

Eric