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SubjectRe: [PATCH 0/16 v6] PCI: Linux kernel SR-IOV support
Anthony Liguori wrote:
> I don't think it's established that PV/VF will have less latency than
> using virtio-net. virtio-net requires a world switch to send a group
> of packets. The cost of this (if it stays in kernel) is only a few
> thousand cycles on the most modern processors.
>
> Using VT-d means that for every DMA fetch that misses in the IOTLB,
> you potentially have to do four memory fetches to main memory. There
> will be additional packet latency using VT-d compared to native, it's
> just not known how much at this time.

If the IOTLB has intermediate TLB entries like the processor, we're
talking just one or two fetches. That's a lot less than the cacheline
bouncing that virtio and kvm interrupt injection incur right now.

--
error compiling committee.c: too many arguments to function



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