Anthony Liguori wrote: > Michael S. Tsirkin wrote: >> >>> This series includes the basic plumbing, as well as the driver for >>> accelerated 802.x (ethernet) networking. >>> >> >> The graphs comparing virtio with vbus look interesting. >> > > 1gbit throughput on a 10gbit link? I have a hard time believing that. > > I've seen much higher myself. Can you describe your test setup in more > detail? Sure, For those graphs, two 8-core x86_64 boxes with Chelsio T3 10GE connected back to back via cross over with 1500mtu. The kernel version was as posted. The qemu version was generally something very close to qemu-kvm.git HEAD at the time the data was gathered, but unfortunately I didn't seem to log this info. For KVM, we take one of those boxes and run a bridge+tap configuration on top of that. We always run the server on the bare-metal machine on the remote side of the link regardless of whether we run the client in a VM or baremetal. For guests, virtio-net and venet connect to the same linux bridge instance, I just "ifdown eth0 / ifup eth1" (or vice versa) and repeat the same test. I do this multiple times (usually about 10) and average the result. I use several different programs, such as netperf, rsync, and ping to take measurements. That said, note that the graphs were from earlier kernel runs (2.6.28, 29-rc8). The most recent data I can find that I published is for 2.6.29, announced with the vbus-v3 release back in April: http://lkml.org/lkml/2009/4/21/408 In it, the virtio-net throughput numbers are substantially higher and possibly more in line with your expectations (4.5gb/s) (though notably still lagging venet, which weighed in at 5.6gb/s). Generally, I find that the virtio-net exhibits non-deterministic results from release to release. I suspect (as we have discussed) the tx-mitigation scheme. Some releases buffer the daylights out of the stream, and virtio gets close(r) throughput (e.g. 4.5g vs 5.8g, but absolutely terrible latency (4000us vs 65us). Other releases it seems to operate with more of a compromise (1.3gb/s vs 3.8gb/s, but 350us vs 85us). I do not understand what causes the virtio performance fluctuation, as I use the same kernel config across builds, and I do not typically change the qemu userspace. Note that some general fluctuation is evident across the board just from kernel to kernel. I am referring to more of the disparity in throughput vs latency than the ultimate numbers, as all targets seem to scale max throughput about the same per kernel. That said, I know I need to redo the graphs against HEAD (31-rc5, and perhaps 30, and kvm.git). I've been heads down with the eventfd interfaces since vbus-v3 so I havent been as active with generating the results. I did confirm that vbus-v4 (alacrityvm-v0.1) still produces a similar graph, but I didn't gather the data as scientifically as I would feel comfortable publishing a graph for. This is on the TODO list. If there is another patch-series/tree I should be using for comparison, please point me at it. HTH Kind Regards, -Greg
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