Re: [PATCH 0/16 v6] PCI: Linux kernel SR-IOV support

[Avi Kivity]

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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