[openib-general] RFC: detecting duplicate MAD requests

[Hal Rosenstock]

On Wed, 2006-06-14 at 15:23, Sean Hefty wrote:
> Hal Rosenstock wrote:
> >>If everyone is okay with breaking the ABI, then I would add send completion 
> >>notification to umad, and put the responsibility on callers not to generate 
> >>duplicate responses.
> > 
> > Is this a better architectural solution ?
> 
> Not sure.

Then it's likely not worth breaking the ABI which will cause more pain
than it's worth.

>   It doesn't solve supporting DS RMPP, which requires maintaining state 
> between receiving a request and the generation of a response.
> 
> > I'm not sure I totally understand what the new ABI would be and its
> > impact on existing applications. Is there an example of what this might
> > look like ?
> 
> Currently, the only send MADs that are reported to the user are requests that 
> time out waiting for a response.  We could probably change that to report all 
> send completions.  Failed sends are reported using a status of timeout, with the 
> MAD header copied to userspace.  So the length of the MAD indicates if it was a 
> send or receive.
> 
>  From an implementation stand point, this approach likely requires only minor 
> changes to the kernel code.  But any userspace applications that send MADs would 
> need to change to handle this.  The list of application that do send MADs is 
> likely fairly small however.

It's not so small.

> If we wanted to be more restrictive on which applications would be affected, we 
> could only generate send completions for response MADs.

I think that would only pare it down a little.

-- Hal

> - Sean