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From: Galen Shipman (gshipman_at_[hidden])
Date: 2007-05-11 15:15:40


>
> As an aside, my personal feeling is that even when running over IB the
> preposting of recvs is worth the small overhead of piggybacking a
> credit
> system on the messages that already cross the wire. If nothing else,
> this avoids adding congestion of RNR-NAKS and the resends they
> trigger.
> Put another way, I favor programming for IB as if it lacked the
> link-level flow control that the current BTL apparently assumes.
>

We avoid the RNR-NAKS in the Open IB BTL via a credit system.
I would have to review the udapl BTL but I believe it does something
similar.
I believe the problem only exists during lazy connection
establishment, when credits are probably initialized to the defaults
on both ends. We should really just set the credits as part of the
handshake (after the receiver has posted the receive buffers).

- Galen

> -Paul
>
> --
> Paul H. Hargrove PHHargrove_at_[hidden]
> Future Technologies Group
> HPC Research Department Tel: +1-510-495-2352
> Lawrence Berkeley National Laboratory Fax: +1-510-486-6900
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