Hi Arnd, On 12/11/20 6:54 pm, Arnd Bergmann wrote: > On Tue, Nov 10, 2020 at 4:42 PM Kishon Vijay Abraham I <kishon@xxxxxx> wrote: >> On 10/11/20 8:29 pm, Arnd Bergmann wrote: >>> On Tue, Nov 10, 2020 at 3:20 PM Kishon Vijay Abraham I <kishon@xxxxxx> wrote: >>>> On 10/11/20 7:55 am, Sherry Sun wrote: >>> >>>>> But for VOP, only two boards are needed(one board as host and one board as card) to realize the >>>>> communication between the two systems, so my question is what are the advantages of using NTB? >>>> >>>> NTB is a bridge that facilitates communication between two different >>>> systems. So it by itself will not be source or sink of any data unlike a >>>> normal EP to RP system (or the VOP) which will be source or sink of data. >>>> >>>>> Because I think the architecture of NTB seems more complicated. Many thanks! >>>> >>>> yeah, I think it enables a different use case all together. Consider you >>>> have two x86 HOST PCs (having RP) and they have to be communicate using >>>> PCIe. NTB can be used in such cases for the two x86 PCs to communicate >>>> with each other over PCIe, which wouldn't be possible without NTB. >>> >>> I think for VOP, we should have an abstraction that can work on either NTB >>> or directly on the endpoint framework but provide an interface that then >>> lets you create logical devices the same way. >>> >>> Doing VOP based on NTB plus the new NTB_EPF driver would also >>> work and just move the abstraction somewhere else, but I guess it >>> would complicate setting it up for those users that only care about the >>> simpler endpoint case. >> >> I'm not sure if you've got a chance to look at [1], where I added >> support for RP<->EP system both running Linux, with EP configured using >> Linux EP framework (as well as HOST ports connected to NTB switch, >> patches 20 and 21, that uses the Linux NTB framework) to communicate >> using virtio over PCIe. >> >> The cover-letter [1] shows a picture of the two use cases supported in >> that series. >> >> [1] -> http://lore.kernel.org/r/20200702082143.25259-1-kishon@xxxxxx > > No, I missed, that, thanks for pointing me to it! > > This looks very promising indeed, I need to read up on the whole > discussion there. I also see your slides at [1] that help do explain some > of it. I have one fundamental question that I can't figure out from > the description, maybe you can help me here: > > How is the configuration managed, taking the EP case as an > example? Your UseCase1 example sounds like the system that owns > the EP hardware is the one that turns the EP into a vhost device, > and creates a vhost-rpmsg device on top, while the RC side would > probe the pci-vhost and then detect a virtio-rpmsg device to talk to. That's correct. Slide no 9 in [1] should give the layering details. > Can it also do the opposite, so you end up with e.g. a virtio-net > device on the EP side and vhost-net on the RC? Unfortunately no. Again referring slide 9 in [1], we only have vhost-pci-epf on the EP side which only creates a "vhost_dev" to deal with vhost side of things. For doing the opposite, we'd need to create virtio-pci-epf for EP side that interacts with core virtio (and also the corresponding vhost back end on PCI host). Thanks Kishon > > Arnd > > [1] https://linuxplumbersconf.org/event/7/contributions/849/attachments/642/1175/Virtio_for_PCIe_RC_EP_NTB.pdf >
