From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: Kernel fast memory registration API proposal [RFC] Date: Tue, 14 Jul 2015 08:33:47 -0700 Message-ID: <20150714153347.GA11026@infradead.org> References: <559F8BD1.9080308@dev.mellanox.co.il> <20150713163015.GA23832@obsidianresearch.com> <55A4CABC.5050807@dev.mellanox.co.il> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <55A4CABC.5050807-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Sagi Grimberg Cc: Jason Gunthorpe , "linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Christoph Hellwig , Steve Wise , Or Gerlitz , Oren Duer , Chuck Lever , Bart Van Assche , Liran Liss , "Hefty, Sean" , Doug Ledford , Tom Talpey List-Id: linux-rdma@vger.kernel.org On Tue, Jul 14, 2015 at 11:39:24AM +0300, Sagi Grimberg wrote: > This is exactly what I don't want to do. I don't think that implicit > posting is a good idea for reasons that I mentioned earlier: > > "This is where I have a problem. Providing an API that may or may not > post a work request on my QP is confusing, and I don't understand its > semantics at all. Do I need to reserve slots on my QP? should I ask for > a completion? If we suppress the completion will I see an error > completion? What should I expect to find in the wr_id?" > > We're much better off with keeping the post interface in place but > have it much simpler. The ULP doesn't care if it needs to reserver the slot, and it generally doesn't care about the notification either unless it needs to handle an error. Instead of the ib_device knows if a MR needs a post it can through a helper set the right reservation. The completions are another mad mightmare in the RDMA stack API. Every other subsystem would just allow submitter to attach a function pointer that handles the completion to the posted item. But no, the RDMA stack instead require ID allocators and gigantic boilerplate code in the consumer to untangle that gigantic mess again. If we sort that out first the ULD doesn't have to care about FR notifications. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html