Hal Rosenstock wrote:
On Sun, 2007-07-01 at 15:05, Gleb Natapov wrote:
On Sun, Jul 01, 2007 at 07:27:24PM +0300, Dror Goldenberg wrote:
SSQ is needed for scalability, no need to explain this (by
the way RD is needed for the same reason too. What's Mellanox
plan to support it?
RD is not supported in hardware today. Implementing RD is extremely
complicated. To solve the scalability issues on MPI like applications
we believe that SRC and SSQ are the right solutions. It is much simpler
for implementation by both software and hardware. By MPI-like I refer
to applications that have some level of trust between two processes of
the
same application. RD also has some performance issues as it only
supports one message in the air. Those performance issues are solved
by design in SRC/SSQ.
Didn't know about RD limitation. Is this shortcomings of IB spec or
general limitation of reliable datagram? RD looks much nice to me then SRC/SSQ.
I think Dror is referring to number of messages in flight per EEC and
number of messages in flight per QP being limited to 1 per IBA spec.
Number of messages enqueued per EEC/QP is implementation dependent.
-- Hal
Correct. The number of messages in flight per EEC is 1 per IB spec.
The fact that IB requires SQ WQEs to complete in order, even if their
destination is different EECs, makes it pretty challenging to have an
implementation that can really process more than one message
simultaneously per QP.
[snip...]
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