linux-kernel - Re: [RFC PATCH 08/11] IB/Verbs: Use management helper has

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Date:	Tue, 31 Mar 2015 15:58:52 +0200
From:	Michael Wang <yun.wang@...fitbricks.com>
To:	Tom Talpey <tom@...pey.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
CC:	"ira.weiny" <ira.weiny@...el.com>,
	Roland Dreier <roland@...nel.org>,
	Sean Hefty <sean.hefty@...el.com>,
	Hal Rosenstock <hal.rosenstock@...il.com>,
	linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-nfs@...r.kernel.org, netdev@...r.kernel.org,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	"David S. Miller" <davem@...emloft.net>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Moni Shoua <monis@...lanox.com>,
	PJ Waskiewicz <pj.waskiewicz@...idfire.com>,
	Tatyana Nikolova <Tatyana.E.Nikolova@...el.com>,
	Yan Burman <yanb@...lanox.com>,
	Jack Morgenstein <jackm@....mellanox.co.il>,
	Bart Van Assche <bvanassche@....org>,
	Yann Droneaud <ydroneaud@...eya.com>,
	Colin Ian King <colin.king@...onical.com>,
	Majd Dibbiny <majd@...lanox.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Matan Barak <matanb@...lanox.com>,
	Alex Estrin <alex.estrin@...el.com>,
	Doug Ledford <dledford@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Erez Shitrit <erezsh@...lanox.com>,
	Sagi Grimberg <sagig@...lanox.com>,
	Haggai Eran <haggaie@...lanox.com>,
	Shachar Raindel <raindel@...lanox.com>,
	Mike Marciniszyn <mike.marciniszyn@...el.com>,
	Steve Wise <swise@...ngridcomputing.com>,
	Tom Tucker <tom@....us>, Chuck Lever <chuck.lever@...cle.com>
Subject: Re: [RFC PATCH 08/11] IB/Verbs: Use management helper has_iwarp()
 for, iwarp-check

On 03/31/2015 03:42 PM, Tom Talpey wrote:

> On 3/31/2015 7:41 AM, Michael Wang wrote:
>> [snip]
> Yes, in fact the iWARP protocol does not preclude multiple read SGEs,
> even though most iWARP implementations have chosen to support just one.
>
> Even for multi-SGE-capable adapters, there is a limit of SGL size, based
> on the adapter's work request format and other factors. So my argument
> is that upper layers can and should query that, not make a blanket
> decision based on protocol type.

Thanks for the explanation  Sounds like some new callback on device level
like query_device() to acquire the right info.

>> I currently only find this one place where infer max-read-sges from
>> transport type, it looks more like a special case to me rather than a generic
>> method we could exposed... and also  not very related with IB management
>> helper concept IMHO.
> It is most certainly not a special case, but you could decide to
> introduce it in many ways. I'm not commenting on that.
>
> My main concern is that you do not introduce a new and clumsy "is iWARP"
> rule as an adapter-specific API requirement to expose the RDMA Read SGE
> behavior. That's what your initial message seemed to imply?

Yeah I planed to just use rdma_transport_iwarp() to replace the check, it's
actually meaningless but just refine, frankly speaking I would prefer some
driver developer to work on that part, at this point I prefer to focus on
introducing the management helpers firstly 

Maybe we could mark it as a TODO temporarily, if later we found more
scenes using similar logical, we can collect them and do some reform 

Regards,
Michael Wang


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