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[Xen-devel] Re: qemu-dm cpu utilization

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Subject: [Xen-devel] Re: qemu-dm cpu utilization
From: Anthony Liguori <anthony@xxxxxxxxxxxxx>
Date: Tue, 29 Aug 2006 19:43:05 -0400
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McAfee, Tommie M wrote:
Using an 8-way ES7000 with 32GB of ram, I'm running xen at changset 11217
with dom0_mem=3092M as a kernel parameter on a x86_64 hyperviser.

It appears that qemu is adding too much overhead to
virtual machines to display graphics.
If I boot a sles9sp3 domVT in runlevel 5 with vga=0x314 for a graphicalboot, 
and immediately use
vncviewer simply to watch the virtual machine as it boots,
qemu-dm consumes 40% cpu as soon as vncviewer is launched and remains that way 
throughout this entire process  without settling down when the login screen 
Even If I close the console that's viewing the virtual host,  qemu-dm remains 
at 40-44%.

Almost everything in the VNC code resets when a guest disconnected except for the timer. If a client disconnects, the timer routine should be almost a nop but it's possible that it's somehow causing qemu-dm to do something funky.

If you delete the timer (and set vs->timer = NULL) in vnc_client_io_error(), does it reduce the usage?

BTW, if you're using 800x600, I suspect that you may be falling back to MMIO instead of a linear framebuffer. Try moving to 1024x768 and see if that helps.


Anthony Liguori

When booting the same domVT in runlevel 5 without ever attempting to connect to 
it with
vncviewer, qemu-dm fluctuated from 1-3% while the host was booting and then 
settled to 0.2% after 4-5 mins.  Assuming that the boot process was complete, I 
launched vncviewer and qemu-dm jumped up to a 40-44% range again.

Lastly I started the same host in runlevel 3 in pure text mode without any
vga parameters on the kernel line, connected to the virtual machine with
vncviewer, and watched the machine boot until a login prompt appeared.  At
this point, top showed qemu-dm as using 0% of the cpu.  Logging into the
virtual machine and running 'startx' however sent qemu-dm back up to a 40-
44% range.

Why is qemu-dm consuming so much of the cpu?  Why is qemu-dm still high
even when I close my vncviewer?

Xen Test Team


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