[ofa-general] Re: [PATCH] ib/core: Add creation flags to create QP

[Eli Cohen]

On Tue, 2008-01-15 at 14:27 -0800, Roland Dreier wrote:
> > On a second thought, we could add - in addition to the creation flags -
>  > a special qp type, IB_QPT_UD_IPOIB for example, where each low level
>  > driver could add special enhancements for the sake of achieving higher
>  > performance. What do you thinks?
> 
> Did you have some specific use for this in mind?  I don't think it's a
> good idea to add this unless there is a really big win we can get.
> 
>  - R.

The idea is that by being able to identify this as a special kind of QP,
the low level driver can provide, for example, a dedicated send function
which can avoid some logic in the data path and thus provide better
results. For example, when the message rate is high (small UDP messages)
and the CPU is fully loaded, reducing the amount of work done in the
send function contributes to increasing the rate.
I have made some changes against the ofed tree and was able to improve
128 bytes UDP throughput from ~280 mpbs to ~500 mpbs. This was measured
on RH4U5 and a special send function was one of the changes I have made
to achieve this. I will post these changes to the list soon.