On Oct 25, 2007, at 11:18 AM, Gleb Natapov wrote:
I don't think xrc should be used by default even if HW supports it.
Only if
special config option is set xrc should be attempted.
Why?
XRC is a crippled RC protocol for scalability sake. Its use makes
progress of one process depend on behaviour of other processes on the
same node which make cause different interesting effects. And of cause
SW flow control is not possible when using XRC, so for small jobs it
will be actually slower. I don't thinks it is wise to use XRC over
regular RC if there is a choice.
Fun stuff. :-)
And xrc availability
can be tested in runtime without additional options in ini file.
Is there a flag on the device / port that indicates XRC availability?
XRC requires creation of special kind of QP. If this fails XRC is not
available.
That's awkward, but ok. :-)
So do you want the arbitration rules for which CPC to be used to be
hard-coded in the openib component (possibly overridden by MCA
parameter to force a specific selection)?
Not hard-coded, but controlled by regular mca mechanism, with default
behaviour dependant on HCA type. Not something new. We have this with
SRQ.
Something like this?
if (mca_specified)
setup to use MCA-specified CPC
else if (iwarp_device)
setup to use rdma_cm CPC
else
setup to use oob CPC
endif
--
Jeff Squyres
Cisco Systems
