On 2013-11-13 16:38, Eric Blake wrote:
> I don't know if qemu exposes a knob for limiting the number of aio
> helper threads it can spawn, or even if that is a good idea.
Those threads do not cause any problems, the host is dealing with a lot
of them and has no problem (CPU usage and load is incredibly low in
practice). Thank you for the clarification, I see why are there more
threads sometimes.
> What domain XML are you using? Yes, there are different disk cache
> policies (writethrough vs. none) which have definite performance vs.
> risk tradeoffs according to the amount of IO latency you want the guest
> to see; but again, the qemu list may be a better help in determining
> which policy is best for your needs. Once you know the policy you want,
> then we can help you figure out how to represent it in the domain XML.
I do not know exactly what is your question, but here is the relevant
part of one the guests:
<domain type='kvm' id='10'>
<name>...</name>
<uuid>...</uuid>
<memory unit='KiB'>2097152</memory>
<currentMemory unit='KiB'>1048576</currentMemory>
<vcpu placement='static'>1</vcpu>
<resource>
<partition>/machine</partition>
</resource>
<os>
<type arch='x86_64' machine='pc-i440fx-1.6'>hvm</type>
<boot dev='hd'/>
</os>
<features>
<acpi/>
<apic/>
<pae/>
</features>
<cpu mode='custom' match='exact'>
<model fallback='allow'>SandyBridge</model>
<vendor>Intel</vendor>
<feature policy='require' name='pbe'/>
...
<feature policy='require' name='monitor'/>
</cpu>
<clock offset='utc'/>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>restart</on_crash>
<devices>
<emulator>/usr/bin/qemu-kvm</emulator>
<disk type='file' device='disk'>
<driver name='qemu' type='raw'/>
<source file='/ssd/vmstorage/web1.raw'/>
<target dev='vda' bus='virtio'/>
<alias name='virtio-disk0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x04'
function='0x0'/>
</disk>
<disk type='file' device='disk'>
<driver name='qemu' type='raw'/>
<source file='/ssd/vmstorage/web1-1.swap'/>
<target dev='vdc' bus='virtio'/>
<alias name='virtio-disk2'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x06'
function='0x0'/>
</disk>
...
<memballoon model='virtio'>
<alias name='balloon0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x05'
function='0x0'/>
</memballoon>
</devices>
<seclabel type='none'/>
</domain>
Currently, the running guests have no "cache" parameter passed to qemu,
so I guess they are using the default qemu setting which is writethrough
according to the QEMU wiki.
(http://en.wikibooks.org/wiki/QEMU/Devices/Storage)
As I understand, moving forward towards more risk and more "performance"
I can try to experiment with "writeback" then?
i.e. <driver name='qemu' type='raw' cache="writeback" />
Cheers.
--
Üdvözlettel / Best regards
Horváth Gergely | gergely.horvath@xxxxxxxxxx
IneTrack - Nyomkövetés egyszerűen | Inepex Kft.
Ügyfélszolgálat: support@xxxxxxxxxxx | +36 30 825 7646 | support.inetrack.hu
Web: www.inetrack.hu | nyomkovetes-blog.hu | facebook.com/inetrack
Inepex - The White Label GPS fleet-tracking platform | www.inepex.com
_______________________________________________
libvirt-users mailing list
libvirt-users@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/libvirt-users
