[libvirt-users] Processor usage of qemu process.

Dominique Ramaekers dominique.ramaekers at cometal.be
Sun Mar 15 08:57:59 UTC 2015

Ok, thanks Andrey.

I experience a behavior that can be placed in your explanation (dough I certainly not a expert :-) ). If SQL guest has a CPU load of 5%, it takes up 50% on the host. Sometimes (late in the evening), the gest cpu load drops to almoust 0% and the host CPU-load drops to about 10% (same as the freshly installed server). So maybe due to the non-activity of the SQL-clients, the SQL-server goes in a kind of rest-state and stops polling for a while until a client accesses the database again or a maintenance plan is started...

I'll settle for now and stop tweaking.

Here below, a summary of tips:
- Setting video to QXL and the display channel to Spice
		 <model type='qxl' ram='65536' vram='65536' heads='1'/>
		<address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
	<channel type='spicevmc'>
		<target type='virtio' name='com.redhat.spice.0'/>
		<address type='virtio-serial' controller='0' bus='0' port='1'/>
- Using HyperV enlightenemt timer
			<relaxed state='on'/>  
			<vapic state='on'/>  
			<spinlocks state='on' retries='8191'/>  
	<clock ...>  
		<timer name='hypervclock' present='yes'/>  
- Delete the tablet entry in the input section

Again thanks Daniel and Andrey.

-----Oorspronkelijk bericht-----
Van: Andrey Korolyov [mailto:andrey at xdel.ru] 
Verzonden: vrijdag 13 maart 2015 20:16
Aan: Dominique Ramaekers
CC: Daniel P. Berrange; libvirt-users at redhat.com
Onderwerp: Re: [libvirt-users] Processor usage of qemu process.

As far as I can understand the mentioned improvement is targeted on a polling mode for a MSSQL, there is no wonder for observing relatively high hypervisor CPU consumption without any sign of same consumption in a guest itself. Certain kinds of applications (PBXes, Chrome/Chromium, seemingly MSSQL) may poll some resource very frequently, causing wakeups in the host for guest process and increasing overall running time of a guest process. I`ve heard of none of the mitigations for this class of workload issues, though you can experiment with guest timer settings if you want to. As we are talking in the libvir-list, it is safe to suggest to use native HyperV host to eliminate this problem completely. :)

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