> > The idea is simple, just to pin the guest VM user space and then let > > host NIC driver has the chance to directly DMA to it. > > > >Isn't it much easier to map the RX ring of the network device into the > >guest's address space, have DMA map calls translate guest addresses to > >physical/DMA addresses as well as do all of this crazy page pinning > >stuff, and provide the translations and protections via the IOMMU? >This means we need guest know how the specific network device works. >So we won't be able to, for example, move guest between different hosts. >There are other problems: many physical systems do not have an iommu, >some guest OS-es do not support DMA map calls, doing VM exit >on each DMA map call might turn out to be very slow. And so on. This solution is what now we can think of to implement zero-copy. Some modifications are made to net core to try to avoid network device driver changes. The major change is to __alloc_skb(), in which we added a dev parameter to indicate whether the device will DMA to/from guest/user buffer which is pointed by host skb->data. We also modify skb_release_data() and skb_reserve(). We made it now works with ixgbe driver with PS mode disabled, and got some performance data with it. using netperf with GSO/TSO disabled, 10G NIC, disabled packet split mode, with raw socket case compared to vhost. bindwidth will be from 1.1Gbps to 1.7Gbps CPU % from 120%-140% to 140%-160% We are now trying to get decent performance data with advanced features. Do you have any other concerns with this solution? >> What's being proposed here looks a bit over-engineered. >This is an attempt to reduce overhead for virtio (paravirtualization). >'Don't use PV' is kind of an alternative, but I do not >think it's a simpler one. -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
