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I have running some Minecraft Servers in a Qemu VM over Libvirt, and the performance is only half good than on real hardware.

Libvirt started the vm over:

/usr/bin/kvm
-S
-M pc-1.1
-cpu SandyBridge,+osxsave,+pdcm,+xtpr,+tm2,+est,+smx,+vmx,+ds_cpl,+monitor,+dtes64,+pbe,+tm,+ht,+ss,+acpi,+ds,+vme
-enable-kvm
-m 28672
-smp 6,sockets=6,cores=1,threads=1
-name Minecraft
-uuid ed7e6bda-2e9f-3895-2ff8-c52c54db588f
-no-user-config
-nodefaults
-chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/Minecraft.monitor,server,nowait
-mon chardev=charmonitor,id=monitor,mode=control
-rtc base=utc
-no-shutdown
-device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2
-drive file=/ssd/vm/Minecraft/boot.img,if=none,id=drive-virtio-disk0,format=raw,cache=writeback
-device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x5,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1
-drive file=/srv/vm/Minecraft/data.img,if=none,id=drive-virtio-disk1,format=raw
-device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x7,drive=drive-virtio-disk1,id=virtio-disk1
-drive if=none,id=drive-ide0-1-0,readonly=on,format=raw
-device ide-cd,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0
-netdev tap,fd=20,id=hostnet0
-device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:49:93:3c,bus=pci.0,addr=0x3
-chardev pty,id=charserial0
-device isa-serial,chardev=charserial0,id=serial0
-device usb-tablet,id=input0
-vnc 127.0.0.1:1
-k de
-vga cirrus
-device intel-hda,id=sound0,bus=pci.0,addr=0x4
-device hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0
-device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x6

Host-CPU: Intel Xeon 1270 V2

Any Ideas to improve the Performance ?

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1 Answer 1

Well...you're segregating the server hardware across multiple servers. Of course you'd take a performance hit. VMs "force" a cap on resources whereas running multiple instances of the server on the physical hardware gets "balanced" by the system itself.

There's also the overhead of KVM in general.

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I'm run only one VM to be more flexible, so there is no segregation –  shim_ Jun 20 '13 at 18:13
    
If you're running only one VM, why one core? -smp 6,sockets=6,cores=1,threads=1 –  Nathan C Jun 20 '13 at 18:17

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