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+performance: 0.968
+graphic: 0.682
+device: 0.648
+semantic: 0.548
+user-level: 0.514
+architecture: 0.456
+peripherals: 0.440
+network: 0.415
+mistranslation: 0.389
+virtual: 0.332
+socket: 0.313
+x86: 0.190
+PID: 0.182
+permissions: 0.171
+ppc: 0.163
+hypervisor: 0.148
+debug: 0.136
+assembly: 0.134
+i386: 0.112
+KVM: 0.111
+register: 0.085
+boot: 0.082
+TCG: 0.072
+kernel: 0.063
+VMM: 0.055
+risc-v: 0.051
+arm: 0.048
+vnc: 0.043
+files: 0.036
+
+Slow UDP performance with virtio device
+
+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.
+
+
+
+Triaging old bug tickets ... can you still reproduce this issue with the latest version of QEMU? Have you already tried vhost?
+
+[Expired for QEMU because there has been no activity for 60 days.]
+