We have an in-house app, written in c, that is not performing as well as we'd
hoped it would when moving to a VM. We've tried all the common tuning
recommendations (virtio, tap interface, cpu pining), without any change in
performance. Even terminating all of the other VMs on the host doesn't make a
difference. The VM doesn't appear to be CPU, memory or IO bound. We are trying
to maximize UDP-based QPS against the in-house app.
I've been running strace against the app and "perf kvm" against the VM to try
to identify any bottlenecks. I would say there are a lot of kvm_exits, but I'm
not sure how to quantify what is acceptable and what is not.
We are trying to maximize UDP queries against the app. I've read a few times
that the virtio network stack results in a lot of vm_exits. Unfortunately, we
can't use the direct PCI access with our hardware.
Is there a good resource "inefficient" system calls? Things that result in
higher than normal kvm_exits, or other performance killers?
Thanks for the help.
Our hypdervisor is running on
CentOS 6.3: 2.6.32-279.22.1.el6.x86_64
qemu-kvm 0.12.1.2
libvirt 0.9.10
Our app is running on
Centos 6.1: 2.6.32-131.0.15.el6.x86_64
<domain type='kvm'>
<name>thing1</name>
<uuid>abe76ce9-60a0-4727-a7ae-cf572e5c3f21</uuid>
<memory unit='KiB'>16384000</memory>
<currentMemory unit='KiB'>16384000</currentMemory>
<vcpu placement='static'>6</vcpu>
<cputune>
<vcpupin vcpu='0' cpuset='0'/>
<vcpupin vcpu='1' cpuset='2'/>
<vcpupin vcpu='2' cpuset='4'/>
<vcpupin vcpu='3' cpuset='6'/>
<vcpupin vcpu='4' cpuset='8'/>
<vcpupin vcpu='5' cpuset='10'/>
</cputune>
<numatune>
<memory mode='interleave' nodeset='0,2,4,6,8,10'/>
</numatune>
<os>
<type arch='x86_64' machine='rhel6.0.0'>hvm</type>
<boot dev='hd'/>
</os>
<features>
<acpi/>
<apic/>
<pae/>
</features>
<clock offset='utc'/>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>restart</on_crash>
<devices>
<emulator>/usr/libexec/qemu-kvm</emulator>
<disk type='file' device='disk'>
<driver name='qemu' type='raw' cache='none'/>
<source file='/var/lib/libvirt/images/thing1-disk0'/>
<target dev='vda' bus='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x05'
function='0x0'/>
</disk>
<controller type='usb' index='0'>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01'
function='0x2'/>
</controller>
<interface type='bridge'>
<mac address='00:5e:e3:e1:8a:aa'/>
<source bridge='virbr0'/>
<model type='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x04'
function='0x0'/>
</interface>
<serial type='pty'>
<target port='0'/>
</serial>
<console type='pty'>
<target type='serial' port='0'/>
</console>
<input type='tablet' bus='usb'/>
<input type='mouse' bus='ps2'/>
<graphics type='vnc' port='-1' autoport='yes' keymap='en-us'/>
<video>
<model type='cirrus' vram='9216' heads='1'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x02'
function='0x0'/>
</video>
<memballoon model='virtio'>
<address type='pci' domain='0x0000' bus='0x00' slot='0x06'
function='0x0'/>
</memballoon>
</devices>
</domain>
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