Messages in this thread | | | Date | Sun, 16 Nov 2008 18:04:55 +0200 | From | Avi Kivity <> | Subject | Re: [PATCH 0/16 v6] PCI: Linux kernel SR-IOV support |
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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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