Richard Frank wrote:
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 ?
Yes, by adding flow control. And it could be iwarp-specific if you
want. I would not suggest relying on connection termination and
re-establishment as the way to handle this :).
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 ?
Don't know yet, but probably as fast.
Why would not push memory window creation into the RDS transport
specific implementations ?
Isn't it already transport-specific? IE you don't need FMRs for TCP.
(I'm ignorant on the specifics of the implementation at this point, so
please excuse any dumb statements :)
Changing the API may be OK - if we retain the performance we have with
IB.
I assume nothing would fly that regresses IB performance. Worst case,
you have an iwarp-specific RDS transport like you do for TCP, I guess.
Hopefully though, IB + iWARP will be a common transport.
Stay tuned for the new verbs API RFC...
Steve.
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