[ofa-general] Re: Re: [PATCH RFC] sharing userspace IB objects

[Hal Rosenstock]

On Mon, 2007-07-02 at 08:58, Dror Goldenberg wrote:
> 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,

Where's this requirement in the spec (and could this be relaxed as it
seems like it is overly "specified") ? Just wondering...

-- Hal

>  makes it pretty challenging to have an 
> implementation that can really process more than one message 
> simultaneously per QP.
> 
> > [snip...]
> >
> >
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>