** Attachment added: "udp-pong.c" http://launchpadlibrarian.net/50751155/udp-pong.c
-- Slow UDP performance with virtio device https://bugs.launchpad.net/bugs/597351 You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. Status in QEMU: New Bug description: I'm working on an app that is very sensitive to round-trip latency between the guest and host, and qemu/kvm seems to be significantly slower than it needs to be. The attached program is a ping/pong over UDP. Call it with a single argument to start a listener/echo server on that port. With three arguments it becomes a counted "pinger" that will exit after a specified number of round trips for performance measurements. For example: $ gcc -o udp-pong udp-pong.c $ ./udp-pong 12345 & # start a listener on port 12345 $ time ./udp-pong 127.0.0.1 12345 1000000 # time a million round trips When run on the loopback device on a single machine (true on the host or within a guest), I get about 100k/s. When run across a port forward using "user" networking on qemu (or kvm, the performance is the same) and the default rtl8139 driver (both the host and guest are Ubuntu Lucid), I get about 10k/s. This seems very slow, but perhaps unavoidably so? When run in the same configuration using the "virtio" driver, I get only 2k/s. This is almost certainly a bug in the virtio driver, given that it's a paravirtualized device that is 5x slower than the "slow" hardware emulation. I get no meaningful change in performance between kvm/qemu.
