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Date: Tue, 31 Mar 2015 09:56:29 -0400 From: Tom Talpey <tom@...pey.com> To: Michael Wang <yun.wang@...fitbricks.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 3/31/2015 7:41 AM, Michael Wang wrote: > Hi, Tom > > Thanks for the comments :-) > > On 03/31/2015 01:19 PM, Tom Talpey wrote: [oops - repeating my reply with full cc's] >> [snip] >> >>> >>> Actually I'm thinking about Doug's idea to use rdma_transport_is_XX() >>> instead of the current basic helper, thus may be use rdma_transport_is_iwarp() >>> in here could be better, since it's actually a feature of iwarp tech >>> that RDMA Read only support one scatter-gather entry. >> >> No, you should expose an attribute to surface the maximum length of >> the remote gather list, which varies by adapter as well as protocol. >> The fact that iWARP is different from IB is not relevant, and conflates >> unrelated properties. > > To be confirmed, so your point is that the max-read-sges will be different > even the transport is the same IWRAP, and that depends on the capability > of adapter, correct? 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. > > 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? -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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