Re: Win10 always takes 100% cpu power even when idle

[Daniel P . Berrangé]

On Wed, Mar 17, 2021 at 05:11:22PM +0100, Reinoud Zandijk wrote:
> Hi,
> 
> when executing Qemu with
> 
>   qemu-system-x86_64 -m 4G -smp cores=2 -M q35 -snapshot \
>     -drive file=/home/reinoud/Downloads/Win10-demo.raw,format=raw \
>     -rtc base=localtime,clock=host -spice port=5924,disable-ticketing=on \
>     -vga qxl -usb -device usb-tablet -net nic -net tap,ifname=tap0,script=no
> 
> my cpu usage in Windows10 *allways* reports 100% cpu usage. On the host system
> its always 190%+ ie it is really taking two cores completely.
> 
> Using our NVMM accelerator makes it run a whole lot faster, as good as native
> speed, but it always takes up the whole two processors too! Windows10 also
> *allways* reports 100% cpu usage. Its not a startup thing for even when
> letting it run for quite some time never reduces the cpu time.
> 
> In contrast, running NetBSD in the VM takes no CPU time at all when idle.
> 
> When Googling about this, I saw this come by quite often. Is there something
> Qemu can do about this? What makes it spin like this and why is it Windows10
> specific? This is a specific VM aware version too if I may believe it saying
> so. I already replaced drivers to virtio etc but to no avail. Always 100% CPU
> time for all CPUs.
> 
> Could this also be an ACPI thing?

IIRC,  "-usb" still adds a USB-1 controller and that's known to be bad
for causing high load in Windows guests in particular. So before
debugging anything else, I'd suggest configuring a USB-3 controller
instead - see docs/usb2.txt XHCI info.


Regards,
Daniel
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