On Fri, 2012-07-27 at 22:09 -0500, sheng qiu wrote: > Hi all, > > i am comparing network throughput performance under bare-metal case > with that running VM with assigned-device (assigned NIC). i have two > physical machines (each has a 10Gbit NIC), one is used as remote > server (run netserver) and the other is used as the target tested one > (run netperf with different send message size, TCP_STREAM test). the > remote NIC is connected directly with the tested NIC, both are 10Gbit. > fore bare-metal case, i enable 1 cpu core, for VM i also configure 1 > vcpu (the memory is sufficient for both bare-metal and VM case). i > run netperf for 120 seconds and got the following results: > > send message interrupts throughput (mbit/s) > bare-metal 256 10696290 1114.84 > 512 10106786 1391.92 > 1024 10071032 1508.09 > 2048 4560857 3434.65 > 4096 3292200 4762.26 > 8192 3169801 4733.89 > 16384 2780529 4892.6 > Are these interrupt counts taken on the receiver ? > VM(assigned NIC) 256 3817904 2249.35 > 512 3599007 4342.81 > 1024 3005601 4134.69 > 2048 2952122 4484 > 4096 2682874 4566.34 > 8192 2786719 4734.39 > 16384 2603835 4540.47 > > as shown, the interrupts for bare-metal case is much more than the VM > case for some message size. we also see the throughput for those > situations is lower than VM case. it's strange that the bare-metal has > lower performance than the VM case. Does anyone have comments on this? > i am very confused. Well, I think you answered to your question. High interrupt rates are not good for throughput. They might be good for latencies. Using a VM adds delays and several frames might be delivered per interrupt. Using bare metal is faster and only one frame is delivered by NIC per interrupt. Try TCP_RR instead of TCP_STREAM for example. What NIC is it exactly ? It seems it has no coalescing or LRO strategy. ethtool -k eth0 ethtool -c eth0 What kernel version as used, because 4892 Mbits is not line rate. -- 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
