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

[Dror Goldenberg]

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...]
>
>
> _______________________________________________
> general mailing list
> general at lists.openfabrics.org
> http://lists.openfabrics.org/cgi-bin/mailman/listinfo/general
>
> To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
>
>