Solved Extreme performance problem - svchost > 90% CPU for hours

[billm5]

Extreme performance degradation over the past few hours, on an otherwise long-stable Windows 7 machine.
Symptoms: Resource Monitor shows 90%+ CPU utilization by svchost.exe (netsvcs) ... but the Services pane (again, within Resource Monitor) does not show any CPU consumption by services (in that process, or elsewhere)... and interactive use doesn't seem to be affected (including posting this message)

AND now ... literally as I was typing the above... the CPU utilization dropped down to near zero. (!?!)

Cue Twilight Zone theme...


(I'll poke around to see if there were any noteworthy changes in the filesystem, of course.)

 

[GokAy]

Any updates appeared in Windows Updates? It may have been checking updates. Do you keep Windows up-to-date?

 

[billm5]

Yes, I believe it was indeed :devil: Windows Update... but it seems odd that Microsoft would ship patches on Friday, Sept. 11 rather than Patch Tuesday (a/k/a today)... but then, "today" has only just begun, in my timezone.

And still no explanation as to why Resource Monitor wasn't displaying the CPU usage as associated with any of the services such as svchost.exe(netsvcs) ... which is often where the CPU usage appears on Patch Tuesday, in my experience.

My machine is configured to download whatever Microsoft sends whenever it's sent, then I selectively apply them (because sometimes Microsoft slips major changes in, "under the covers," so I want to be able to schedule other major workloads to not compete for resources with WinUpd).

This month's batch of updates was certainly massive!