netdev - Re: [PATCH v2 01/17] IB/Verbs: Implement new callback query

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Date:	Wed, 08 Apr 2015 16:55:31 -0400
From:	Tom Talpey <tom@...pey.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Doug Ledford <dledford@...hat.com>
CC:	Michael Wang <yun.wang@...fitbricks.com>,
	Roland Dreier <roland@...nel.org>,
	Sean Hefty <sean.hefty@...el.com>, linux-rdma@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
	netdev@...r.kernel.org, Hal Rosenstock <hal.rosenstock@...il.com>,
	Tom Tucker <tom@...ngridcomputing.com>,
	Steve Wise <swise@...ngridcomputing.com>,
	Hoang-Nam Nguyen <hnguyen@...ibm.com>,
	Christoph Raisch <raisch@...ibm.com>,
	Mike Marciniszyn <infinipath@...el.com>,
	Eli Cohen <eli@...lanox.com>,
	Faisal Latif <faisal.latif@...el.com>,
	Upinder Malhi <umalhi@...co.com>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"David S. Miller" <davem@...emloft.net>,
	Ira Weiny <ira.weiny@...el.com>,
	PJ Waskiewicz <pj.waskiewicz@...idfire.com>,
	Tatyana Nikolova <Tatyana.E.Nikolova@...el.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Jack Morgenstein <jackm@....mellanox.co.il>,
	Haggai Eran <haggaie@...lanox.com>,
	Ilya Nelkenbaum <ilyan@...lanox.com>,
	Yann Droneaud <ydroneaud@...eya.com>,
	Bart Van Assche <bvanassche@....org>,
	Shachar Raindel <raindel@...lanox.com>,
	Sagi Grimberg <sagig@...lanox.com>,
	Devesh Sharma <devesh.sharma@...lex.com>,
	Matan Barak <matanb@...lanox.com>,
	Moni Shoua <monis@...lanox.com>, Jiri Kosina <jkosina@...e.cz>,
	Selvin Xavier <selvin.xavier@...lex.com>,
	Mitesh Ahuja <mitesh.ahuja@...lex.com>,
	Li RongQing <roy.qing.li@...il.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Alex Estrin <alex.estrin@...el.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Erez Shitrit <erezsh@...lanox.com>,
	Tom Gundersen <teg@...m.no>,
	Chuck Lever <chuck.lever@...cle.com>
Subject: Re: [PATCH v2 01/17] IB/Verbs: Implement new callback query_transport()
 for each HW

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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