On 20/6/19 2:35 μ.μ., Maxime Coquelin wrote: > Hi Nikos, > > On 6/19/19 5:14 PM, Nikos Dragazis wrote: >> Hi everyone, >> >> this patch series introduces the concept of the virtio-vhost-user >> transport. This is actually a revised version of an earlier RFC >> implementation that has been proposed by Stefan Hajnoczi [1]. Though >> this is a great feature, it seems to have been stalled, so I’d like to >> restart the conversation on this and hopefully get it merged with your >> help. Let me give you an overview. > > Thanks for taking over the series! > > I think you are already aware of that, but it arrives too late to > consider it for v19.08, as the proposal deadline is over by almost 3 > weeks. > > That said, it is good that you sent it early, so that we can work to > make it in for v19.11.
That's totally fine. > >> The virtio-vhost-user transport is a vhost-user transport implementation >> that is based on the virtio-vhost-user device. Its key difference with >> the existing transport is that it allows deploying vhost-user targets >> inside dedicated Storage Appliance VMs instead of host user space. In >> other words, it allows having guests that act as vhost-user backends for >> other guests. >> >> The virtio-vhost-user device implements the vhost-user control plane >> (master-slave communication) as follows: >> >> 1. it parses the vhost-user messages from the vhost-user unix domain >> socket and forwards them to the slave guest through virtqueues >> >> 2. it maps the vhost memory regions in QEMU’s process address space and >> exposes them to the slave guest as a RAM-backed PCI MMIO region >> >> 3. it hooks up doorbells to the callfds. The slave guest can use these >> doorbells to interrupt the master guest driver >> >> The device code has not yet been merged into upstream QEMU, but this is >> definitely the end goal. > > Could you provide a pointer to the QEMU series, and instructions to test > this new device? Of course. Please have a look at the following step-by-step guide: https://github.com/ndragazis/ndragazis.github.io/blob/master/dpdk-vhost-vvu-demo.md If you face any problems or you find that something breaks (I hope not :) ) please let me know. I haven't done thorough testing so I may have missed something. Please, also bear in mind that the device code is not finished. There are still some things that need to be done. > >> The current state is that we are awaiting for >> the approval of the virtio spec. > > Ditto, a link to the spec patches would be useful. You can find the patches here: https://lists.oasis-open.org/archives/virtio-dev/201905/msg00022.html and an HTML version is available here: https://ndragazis.github.io/virtio-v1.1-wd02.html#x1-41000011 > >> I have Cced Darek from the SPDK community who has helped me a lot by >> reviewing this series. Note that any device type could be implemented >> over this new transport. So, adding the virtio-vhost-user transport in >> DPDK would allow using it from SPDK as well. >> >> Getting into the code internals, this patch series makes the following >> changes: >> >> 1. introduce a generic interface for the transport-specific operations. >> Each of the two available transports, the pre-existing AF_UNIX >> transport and the virtio-vhost-user transport, is going to implement >> this interface. The AF_UNIX-specific code has been extracted from the >> core vhost-user code and is now part of the AF_UNIX transport >> implementation in trans_af_unix.c. >> >> 2. introduce the virtio-vhost-user transport. The virtio-vhost-user >> transport requires a driver for the virtio-vhost-user devices. The >> driver along with the transport implementation have been packed into >> a separate library in `drivers/virtio_vhost_user/`. The necessary >> virtio-pci code has been copied from `drivers/net/virtio/`. Some >> additional changes have been made so that the driver can utilize the >> additional resources of the virtio-vhost-user device. >> >> 3. update librte_vhost public API to enable choosing transport for each >> new vhost device. Extend the vhost net driver and vhost-scsi example >> application to export this new API to the end user. >> >> The primary changes I did to Stefan’s RFC implementation are the >> following: >> >> 1. moved postcopy live migration code into trans_af_unix.c. Postcopy >> live migration relies on the userfault fd mechanism, which cannot be >> supported by virtio-vhost-user. >> >> 2. moved setup of the log memory region into trans_af_unix.c. Setting up >> the log memory region involves mapping/unmapping guest memory. This >> is an AF_UNIX transport-specific operation. >> >> 3. introduced a vhost transport operation for >> process_slave_message_reply() >> >> 4. moved the virtio-vhost-user transport/driver into a separate library >> in `drivers/virtio_vhost_user/`. This required making vhost.h and >> vhost_user.h part of librte_vhost public API and exporting some >> private symbols via the version script. This looks better to me that >> just moving the entire librte_vhost into `drivers/`. I am not sure if >> this is the most appropriate solution. I am looking forward to your >> suggestions on this. > > I'm not sure this is the right place to put it. Okay. Is there something specific that you think that doesn't fit nicely? Do you have something else in mind? > >> 5. made use of the virtio PCI capabilities for the additional device >> resources (doorbells, shared memory). This required changes in >> virtio_pci.c and trans_virtio_vhost_user.c. >> >> 6. [minor] changed some commit headlines to comply with >> check-git-log.sh. >> >> Please, have a look and let me know about your thoughts. Any >> reviews/pointers/suggestions are welcome. > > Maxime
