Ira W. Snyder wrote: > On Mon, Sep 07, 2009 at 01:15:37PM +0300, Michael S. Tsirkin wrote: >> On Thu, Sep 03, 2009 at 11:39:45AM -0700, Ira W. Snyder wrote: >>> On Thu, Aug 27, 2009 at 07:07:50PM +0300, Michael S. Tsirkin wrote: >>>> What it is: vhost net is a character device that can be used to reduce >>>> the number of system calls involved in virtio networking. >>>> Existing virtio net code is used in the guest without modification. >>>> >>>> There's similarity with vringfd, with some differences and reduced scope >>>> - uses eventfd for signalling >>>> - structures can be moved around in memory at any time (good for migration) >>>> - support memory table and not just an offset (needed for kvm) >>>> >>>> common virtio related code has been put in a separate file vhost.c and >>>> can be made into a separate module if/when more backends appear. I used >>>> Rusty's lguest.c as the source for developing this part : this supplied >>>> me with witty comments I wouldn't be able to write myself. >>>> >>>> What it is not: vhost net is not a bus, and not a generic new system >>>> call. No assumptions are made on how guest performs hypercalls. >>>> Userspace hypervisors are supported as well as kvm. >>>> >>>> How it works: Basically, we connect virtio frontend (configured by >>>> userspace) to a backend. The backend could be a network device, or a >>>> tun-like device. In this version I only support raw socket as a backend, >>>> which can be bound to e.g. SR IOV, or to macvlan device. Backend is >>>> also configured by userspace, including vlan/mac etc. >>>> >>>> Status: >>>> This works for me, and I haven't see any crashes. >>>> I have done some light benchmarking (with v4), compared to userspace, I >>>> see improved latency (as I save up to 4 system calls per packet) but not >>>> bandwidth/CPU (as TSO and interrupt mitigation are not supported). For >>>> ping benchmark (where there's no TSO) troughput is also improved. >>>> >>>> Features that I plan to look at in the future: >>>> - tap support >>>> - TSO >>>> - interrupt mitigation >>>> - zero copy >>>> >>> Hello Michael, >>> >>> I've started looking at vhost with the intention of using it over PCI to >>> connect physical machines together. >>> >>> The part that I am struggling with the most is figuring out which parts >>> of the rings are in the host's memory, and which parts are in the >>> guest's memory. >> All rings are in guest's memory, to match existing virtio code. > > Ok, this makes sense. > >> vhost >> assumes that the memory space of the hypervisor userspace process covers >> the whole of guest memory. > > Is this necessary? Why? The assumption seems very wrong when you're > doing data transport between two physical systems via PCI. FWIW: VBUS handles this situation via the "memctx" abstraction. IOW, the memory is not assumed to be a userspace address. Rather, it is a memctx-specific address, which can be userspace, or any other type (including hardware, dma-engine, etc). As long as the memctx knows how to translate it, it will work. Kind Regards, -Greg
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