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Description of problem: Boot a rhel6.8 guest w/ a virtio-net-pci device, but w/o vhost=on, when test netperf and protocol UDP_STREAM inside guest, during the stress, guest can not response any other things, such as click mouse, input keys ... If boot w/vhost=off,sndbuf=1048576,won't hit this issue. If boot w/ vhost=on, won't hit this problem. Version-Release number of selected component (if applicable): 2.6.32-595.el6.x86_64 qemu-kvm-0.12.1.2-2.483.el6.x86_64 How reproducible: 100% Steps to Reproduce: 1.Boot a rhel6.8 guest w/ virtio-net-pci device but do not add option vhost=on. 2.In any external host run a netserver, and in this guest test nerperf w/ protocol UDP_STREAM # netperf -H 10.66.9.230 -t UDP_STREAM -l 30 3.On the spice window, try to type or click or send ctrl-alt-f2 Actual results: From the spice window(w/ GUI), can not do anything, seams lose response. Expected results: guest works well Additional info: /usr/libexec/qemu-kvm \ -name rhel6.8 -machine pc \ -drive id=drive_image1,if=none,cache=none,snapshot=on,format=qcow2,file=/mnt/RHEL-Server-6.7-64-virtio.qcow2 \ -device virtio-blk-pci,id=image1,drive=drive_image1,bus=pci.0,bootindex=0 \ -netdev tap,id=hostnet0,vhost=off \ -device virtio-net-pci,netdev=hostnet0,mac=52:56:25:93:79:66,id=net0,status=on,ioeventfd=on \ -m 4096 \ -smp 4,maxcpus=8,cores=4,threads=1,sockets=1 \ -cpu SandyBridge \ -boot menu=on -enable-kvm \ -qmp tcp:0:5555,nowait,server \ -monitor stdio \ -spice port=5900,disable-ticketing \ -global qxl-vga.vram_size=67108864 \ -vga qxl \ -chardev socket,path=/tmp/qga.sock,server,nowait,id=qga0 \ -device virtio-serial -device virtserialport,chardev=qga0,name=org.qemu.guest_agent.0
What qdisc did you use in guest? This is probably a known issue since no tx completion interrups for virtio-net.
Defer to 6.10. Well known issues upstream if using a non fair queuing qdisc in host or guest tx buffer bloat.
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