Tom Horsley writes:
Here's a weird one I just noticed: I've been using a
Windows 10 virtual machine to run my tax software.
I've got it displayed in virt-viewer and all is
well, then I close the virt-viewer window and
leave the KVM running. About 5 minutes later I
see a cpu suddenly pegged at 100%. I run top and see
that qemu is the culprit. I start virt-viewer
again, and it goes back to normal.
Anyone else seen this? Why would nobody looking at
it make it go crazy I wonder?
Because you're using Microsoft Windows 10. Its built-in spyware and
telemetry, that runs all the time and needs to report to Redmond, isn't cost-
free and is pretty hard on the CPU.
Recall that story, about a week ago, when they caught spear-phishing malware
being spread on Huawei-manufactured Win10 boxes, by hacking into Huawei's
driver update system? You probably skimmed the headlines, and might've read
some lightweight stories on that. Try to find some more in-depth coverage of
that, and read it. The hack was discovered by Microsoft from uploaded
telemetry collected from end-user PCs, in the wild. Microsoft's Windows 10
telemetry detected Huawei drivers making kernel calls that you don't
normally expect hardware drivers of that type to make, and reported that to
Microsoft.
That kind of internal monitoring is not cheap, you know. In your case,
Windows 10 detects you're not using it, it's idle, so it has a lot of work
to catch up, and starts uploading all the collected telemetry to the
mothership. Microsoft simply wants to make sure you're not hacked, you know.
That takes some serious CPU cost.
Don't even bother closing down the window. Just reboot, and do nothing with
windows 10. Just sit there with an open desktop. Within 5 minutes the CPU
will quickly spike, and get pegged at 100% for maybe 10-15 minutes, before
everything finishes.
It's worse if you don't change the default option that enables "fast
startup", or whatever it's called. That's when Windows 10 "shut
down" isn't
really shut down, but more like "suspend to disk", and then pretend that it
shuts down, so that the next boot allegedly goes faster.
I'm pretty sure, after observing the behavior for some time, that Windows'
equivalent of cron, after such a "fast startup", suddenly realizes that all
the regularly-scheduled telemetry hasn't run in a while, and starts
everything immediately, generating some serious wattage from the CPU.
I did not notice any measurable difference in startup speed after disabling
"fast startup". Windows 10 still spins on the CPU post-boot, doing its
telemetry stuff, but gets it done noticably faster, and goes down to its
idle state much quicker.