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Subject: Re: [OMPI devel] OMPI OpenIB Credit Schema breaks Chelsio HW
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2008-03-10 11:05:35


On Mar 10, 2008, at 9:57 AM, Steve Wise wrote:

> A single PP QP might be fine for now, and chelsio's next-gen part will
> support SRQs and not have this funky issue.

Good!

> But why use such a large buffer size for a single PP QP? Why not use
> something around 16KB?

You can do that, but you'll also need to make the max_send_size be
16kb (and therefore ob1 will switch to rendezvous protocol above that
size). See our paper on the long message protocol that OMPI uses --
the minimum "large" message size was specifically designed to be kinda
big so that we could do some send/recv to offset the registration
penalty of pinning user's large buffers.

-- 
Jeff Squyres
Cisco Systems