Steve Wise wrote:
Olaf Kirch wrote:
On Monday 12 May 2008 18:57:38 Jon Mason wrote:
As part of my effort to get RDS working for iWARP, I will be working
on the RDS flow control. Flow control is needed for iWARP due to
the fact that iWARP connections terminate if there is no posted recv
for an incoming packet. IB connections do not have this limitation
if setup in a certain way. In its current implementation, RDS sets
the connection attribute rnr_retry to 7. This causes IB to
retransmit until there is a posted recv buffer.
I think for the initial implementation, it is fine for iWARP to just
fail the connect when that happens, and re-establish the connection.
If you use reasonable defaults for the send and recv queues, receiver
overruns should be relatively rare.
Once everything else works, let's revisit the flow control part.
I _think_ you'll hit this quickly with one-way flows. Send
completions for iWARP only mean the user's buffer can be reused. Not
that its placed at the remote peer or in the remote user's buffer.
Let's see what happens - anyway - this could be solved in an IWARP
extension to RDS - right ?
But perhaps I'm wrong. Jon, maybe you should try to hit this with IB
and rnr_retry == 0 using the rds perf tools?
Also "the everything else" part depends on remove fmr usage. I'm
working on the new RDMA memory verbs allowing fast registration of
physical memory via a send WR. To support iWARP we need to remove the
fmr usage from RDS. The idea was to replace fmrs with the new
fastreg verbs. Thoughts?
What does "fast" imply here - how does this compare to the performance
of FMRs ?
Why would not push memory window creation into the RDS transport
specific implementations ?
Changing the API may be OK - if we retain the performance we have with IB.
Stay tuned for the new verbs API RFC...
Steve.
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