netdev - Re: [ofa-general] Re: [PATCH RFC] RDMA/CMA: Allocate PS

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Date:	Fri, 17 Aug 2007 12:52:39 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	David Miller <davem@...emloft.net>
Cc:	tom@...ngridcomputing.com, jeff@...zik.org,
	swise@...ngridcomputing.com, mshefty@...ips.intel.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	general@...ts.openfabrics.org
Subject: Re: [ofa-general] Re: [PATCH RFC] RDMA/CMA: Allocate PS_TCP ports from the host TCP port space.

 > > Isn't RDMA _part_ of the "software net stack" within Linux?

 > It very much is not so.

This is just nit-picking.  You can draw the boundary of the "software
net stack" wherever you want, but I think Sean's point was just that
RDMA drivers already are part of Linux, and we all want them to get
better.

 > When using RDMA you lose the capability to do packet shaping,
 > classification, and all the other wonderful networking facilities
 > you've grown to love and use over the years.

Same thing with TSO and LRO and who knows what else.  I know you're
going to make a distinction between "stateless" and "stateful"
offloads, but really it's just an arbitrary distinction between things
you like and things you don't.

 > Imagine if you didn't know any of this, you purchase and begin to
 > deploy a huge piece of RDMA infrastructure, you then get the mandate
 > from IT that you need to add firewalling on the RDMA connections at
 > the host level, and "oh shit" you can't?

It's ironic that you bring up firewalling.  I've had vendors of iWARP
hardware tell me they would *love* to work with the community to make
firewalling work better for RDMA connections.  But instead we get the
catch-22 of your changing arguments -- first, you won't even consider
changes that might help RDMA work better in the name of
maintainability; then you have to protect poor, ignorant users from
accidentally using RDMA because of some problem or another; and then
when someone tries to fix some of the problems you mention, it's back
to step one.

Obviously some decisions have been prejudged here, so I guess this
moves to the realm of politics.  I have plenty of interesting
technical stuff, so I'll leave it to the people with a horse in the
race to find ways to twist your arm.

 - R.
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