Re: [PATCH v2 01/17] IB/Verbs: Implement new callback query_transport() for each HW

From: Tom Talpey
Date: Wed Apr 08 2015 - 16:55:46 EST

On 4/8/2015 4:10 PM, Jason Gunthorpe wrote:
On Wed, Apr 08, 2015 at 02:29:46PM -0400, Doug Ledford wrote:


rdma_port_get_read_sge(dev, port)
if (rdma_transport_is_iwarp)
return 1;
return dev->port[port]->max_sge;

Hum, that is nice, but it doesn't quite fit with how the ULP needs to
work. The max limit when creating a WR is the value passed into the
qp_cap, not the device maximum limit.

Agreed, and I will again say that not all devices necessarily support
the same max_sge for all WR types. The current one-size-fits-all API
may make the upper layer think so, but it's possibly being lied to.

To do this properly we need to extend the qp_cap, and that is just too
big a change. A one bit iWarp quirk is OK for now.

Yes, it would be a large-ish change, and I like Doug's choice of word
"quirk" to capture these as exceptions, until the means for addressing
them is decided.

Overall, I like Doug's proposals, especially from an upper layer
perspective. I might suggest further refining them into categories, perhaps "management", primarily of interest to kernel and the
plumbing of connections; and actual "RDMA semantics", of interest
to RDMA consumers.

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