[openib-general] [PATCH 1/2] perftest: enhancement to rdma_bw to allow useofRDMA CM

[Michael S. Tsirkin]

Quoting r. Steve Wise <swise at opengridcomputing.com>:
> Subject: Re: [PATCH 1/2] perftest: enhancement to rdma_bw to allow useofRDMA CM
> 
> On Thu, 2006-07-06 at 17:57 +0300, Michael S. Tsirkin wrote:
> > Quoting r. Steve Wise <swise at opengridcomputing.com>:
> > > Subject: Re: [PATCH 1/2] perftest: enhancement to rdma_bw to allow use ofRDMA CM
> > > 
> > > On Thu, 2006-07-06 at 09:20 +0300, Michael S. Tsirkin wrote:
> > > > Quoting r. Steve Wise <swise at opengridcomputing.com>:
> > > > > For instance, in the bi-directional bandwidth tests, one side could
> > > > > finish the test and issue an rdma_disconnect() while the other end still
> > > > > has pending rdma writes.  This is an error condition in iWARP.  So they
> > > > > sync up at the end with a message exchange before disconnecting.
> > > > > 
> > > > > Make sense?
> > > > 
> > > > I see. Is this the only message exchange there is?
> > > 
> > > 
> > > There are 2 message exchanges to comply with IWARP spec: 
> > > 
> > > 1) an exchange right after connection setup to force the client to be
> > > the first side to send an RDMA message.  So the server waits for a RECV
> > > completion and the client posts a "lets start" SEND.
> > 
> > I don't get this one.  Why can't we just look at command line arguments for
> > this?  Whoever got the remote IP is the client.  What do you mean by "force
> > client to be the first"?
> 
> This is an iWARP spec/compliance issue.  The client MUST send the first
> RDMA message.  The server CANNOT send an RDMA message until one is
> received from the client.  We've discussed this before on the openib
> list.

So, what you do is post a 0-sized RDMA and then a SEND right after that
as part of the setup? I see.

> (If you want gory details on this, I'll find the original thread
> where we discussed this). 

Might be an interesting read.

-- 
MST