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Subject: Re: [OMPI devel] OMPI OpenIB Credit Schema breaks Chelsio HW
From: Steve Wise (swise_at_[hidden])
Date: 2008-03-10 14:52:22


Jeff Squyres wrote:
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.

  

Does OMPI do lazy dereg to maintain a cache of registered user buffers?