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Message-ID: <1b79048f-4495-3840-e7a6-d4fa5a8dfb57@grimberg.me> Date: Thu, 4 May 2017 11:43:50 +0300 From: Sagi Grimberg <sagi@...mberg.me> To: Bart Van Assche <Bart.VanAssche@...disk.com>, "hch@....de" <hch@....de>, "davem@...emloft.net" <davem@...emloft.net>, "ubraun@...ux.vnet.ibm.com" <ubraun@...ux.vnet.ibm.com> Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org> Subject: Re: net/smc and the RDMA core >> if you can point out specific issues, we will be happy to work with you >> to get them addressed! > > Hello Ursula, > > My list of issues that I would like to see addressed can be found below. Doug, > Christoph and others may have additional inputs. The issues that have not yet > been mentioned in other e-mails are: > - The SMC driver only supports one RDMA transport type (RoCE v1) but > none of the other RDMA transport types (RoCE v2, IB and iWARP). New > RDMA drivers should support all RDMA transport types transparently. > The traditional approach to support multiple RDMA transport types is > by using the RDMA/CM to establish connections. > - The implementation of the SMC driver only supports RoCEv1. This is > a very unfortunate choice because: > - RoCEv1 is not routable and hence is limited to a single Ethernet > broadcast domain. > - RoCEv1 packets escape a whole bunch of mechanisms that only work > for IP packets. Firewalls pass all RoCEv1 packets and switches > do not restrict RoCEv1 packets to a single VLAN. This means that > if the network configuration is changed after an SMC connection > has been set up such that IP communication between the endpoints > of an SMC connection is blocked that the SMC RoCEv1 packets will > not be blocked by the network equipment of which the configuration > has just been changed. > - As already mentioned by Christoph, the SMC implementation uses RDMA > calls that probably will be deprecated soon (ib_create_cq()) and > should use the RDMA R/W API instead of building sge lists itself. I would also suggest that you stop exposing the DMA MR for remote access (at least by default) and use a proper reg_mr operations with a limited lifetime on a properly sized buffer. Also, the cq polling code looks completely wrong, you should really use the RDMA CQ API.
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