[ofa-general] verbs/hardware question

[Doug Ledford]

On Thu, 2007-10-11 at 12:39 -0500, Steve Wise wrote:
> Doug Ledford wrote:
> > So, one of the options when creating a QP is the max inline data size.
> > If I understand this correctly, for any send up to that size, the
> > payload of that send will be transmitted to the receiving side along
> > with the request to send.  
> 
> What it really means is the payload is DMA'd to the HW on the local side 
> in the work request itself as opposed being DMA'd down in a 2nd 
> transaction after the WR is DMA'd and processed.  It has no end-to-end 
> significance.  Other than to reduce the latency needed to transfer the data.

OK, that clears things up for me ;-)

> > This reduces back and forth packet counts on
> > the wire in the case that the receiving side is good to go, because it
> > basically just responds with "OK, got it" and you're done.  
> 
> I don't think this is true.  Definitely not with iWARP.  INLINE is just 
> an optimization to push small amts of data downto the local adapter as 
> part of the work request, thus avoiding 2 DMA's.

> Even though you create the QP with the inline option, only WRs that pass 
> in the IBV_SEND_INLINE flag will do inline processing, so you can 
> control this functionality at a per-WR basis.

Hmm..that raises a question on my part.  You don't call ibv_reg_mr on
the wr itself, so if the data is pushed with the wr, do you still need
to call ibv_reg_mr on the data separately?

-- 
Doug Ledford <dledford at redhat.com>
              GPG KeyID: CFBFF194
              http://people.redhat.com/dledford

Infiniband specific RPMs available at
              http://people.redhat.com/dledford/Infiniband
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