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

[Michael S. Tsirkin]

> Quoting Gleb Natapov <glebn at voltaire.com>:
> Subject: Re: Re: [PATCH RFC] sharing userspace IB objects
> 
> On Tue, Jun 26, 2007 at 10:06:41AM +0300, Michael S. Tsirkin wrote:
> > >    Is there really a strong use case for making every type of object
> > >    shareable?  Can we handle the SRC stuff without going to this
> > >    extreme of complexity?
> > 
> > This is not directly related to SRC: this is an effort
> > to make it possible to share QPs, CQ etc across processes
> > in the same way as they can be currently shared across threads.
> > So assuming that we want multiple processes to post to
> > the same QP, how can we support this?
> 
> Are you absolutely sure you even want to support this?

Take a look here :)
http://www.quotedb.com/quotes/1007

> What is the user case?

Use case? Scalability. Pls go over Dror's presentation given at Sonoma -
he calls this SSQ.

> If multiple processes what to post to the same QP how will you
> ensure that right process will receive right completion event?

Same as with threads - memory for CQEs and locks will be allocated
in shared memory to make it possible for multiple processes to poll
CQ simultaneously, and they get completions in FCFS order.
What to do with them is up to the user.

> Or they
> will be required to allocated send descriptors from a shared memory too?

Yes, send descriptors will have to be placed in shared memory.

> I you want them to receive from the same QP they better allocate receive
> descriptors/buffers from shared memory too.

Yes, this will work, too.
With RDMA, you can have per-process receive buffers.
The SRC extension presented by Dror at Sonoma will make it possible
for SEND operations. I plan to open a separate thread to discuss SRC API.

-- 
MST