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

[Anthony Liguori <anthony@xxxxxxxxxxxxx>]

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 
> appears.
> 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.
Regards,

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?
>
> Tommie,
> Xen Test Team
> Unisys 
>
>
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