I'm not sure yet, but I think the TSO problem affects much more setups, not only windows guests. You might try to set GSO to off in windows guests too, if there is such an option (GSO might be a linux kernel feature).
I currently think that we have similar problems with centos7 hosts and guests as well as with some windows7 guests. I also read about similar centos6 problems. There is even a original setup guide for centos6 from redhat, to set "tso off gso off" in the host bridge adapter, when you use virtio. This whole topic is disturbingly distributed through several setups. The diagnosis of this problem is far from being trivial. -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1202289 Title: Windows 2008/7 Guest to Guest Very slow 10-20Mbit/s Status in QEMU: New Bug description: I'm not sure if I'm submitting this to the proper place or not, if not, please direct me accordingly. At this point I'm starting to get desperate, I'll take any options or suggestions that spring to mind: Anyway, the problem exists on multiple hosts of various quality. From 4 core 8g mem machines to 12 core 64Gig mem machines with LVM and Raid-10. Using iperf as the testing utility: (windows guest can be either Windows 7 or 2008R2) -Windows Guest -> Windows Guest averages 20Mbit/s (The problem) -Windows Guest -> Host averages 800Mbit/s -Host -> Windows Guest averages 1.1Gbit/s -Linux Guest -> Host averages 12GBit/s -Linux Guest -> Linux Guest averages 10.2Gbit/s For windows guests, switching between e1000 and virtio drivers doesn't make much of a difference. I use openvswitch to handle the bridging (makes bonding nics much easier) Disabling TSO GRO on all the host nics, and virtual nics, as well as modding the registry using: netsh int tcp set global (various params here) can slightly improve Windows -> windows throughput. up to maybe 100Mbit/s but even that is spotty at best. The Particulars of the fastest host which benchmarks about the same as the slowest host. Ubuntu 12.04 64bit (updated to lastest as of July 15th) Linux cckvm03 3.5.0-36-generic #57~precise1-Ubuntu SMP Thu Jun 20 18:21:09 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux libvirt: Source: libvirt Version: 0.9.8-2ubuntu17.10 qemu-kvm Package: qemu-kvm Version: 1.0+noroms-0ubuntu14.8 Replaces: kvm (<< 1:84+dfsg-0ubuntu16+0.11.0), kvm-data, qemu openvswitch Source: openvswitch Version: 1.4.0-1ubuntu1.5 /proc/cpuifo processor : 0 vendor_id : GenuineIntel cpu family : 6 model : 45 model name : Intel(R) Xeon(R) CPU E5-2440 0 @ 2.40GHz stepping : 7 microcode : 0x70d cpu MHz : 2400.226 cache size : 15360 KB physical id : 0 siblings : 12 core id : 0 cpu cores : 6 apicid : 0 initial apicid : 0 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdt scp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc ap erfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdc m pcid dca sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx lahf_lm ida arat xsaveopt pln pts dtherm tpr_shadow vnmi flexpriority ept vpid bogomips : 4800.45 clflush size : 64 cache_alignment : 64 address sizes : 46 bits physical, 48 bits virtual power management: -Sample KVM line usr/bin/kvm -S -M pc-1.0 -enable-kvm -m 4096 -smp 2,sockets=2,cores=1,threads=1 -name gvexch01 -uuid d28ffb4b-d809-3b40-ae3d-2925e6995394 -nodefconfig -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/gvexch01.monitor,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=localtime -no-shutdown -boot order=dc,menu=on -drive file=/dev/vgroup/gvexch01,if=none,id=drive-virtio-disk0,format=raw,cache=none,aio=native -device virtio-blk-pci,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-disk0 -drive file=/dev/vgroup/gvexch01-d,if=none,id=drive-virtio-disk1,format=raw,cache=none -device virtio-blk-pci,bus=pci.0,addr=0x6,drive=drive-virtio-disk1,id=virtio-disk1 -drive if=none,media=cdrom,id=drive-ide0-0-0,readonly=on,format=raw -device ide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0 -netdev tap,fd=18,id=hostnet0,vhost=on,vhostfd=21 -device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:bf:4e:1c,bus=pci.0,addr=0x3 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -usb -device usb-tablet,id=input0 -vnc 127.0.0.1:2 -vga std -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x5 To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1202289/+subscriptions
