On my Dell Precision M6700 Mobile Workstation, as well as on my other non-Dell laptop sharing the same Intel 7-series / C216 QM77 chipset (Panther Point), with both laptops running up-to-date Windows 7 Professional 64-bit, there are regular spikes of CPU usage going up to 100% every 15 seconds when streaming audio via USB 2.0 Audio Class Compliant audio interface, occasionally amounting to audio dropouts. LatencyMon v6.5 utility reports that humongous amount of CPU time is being spent inside the usbport.sys driver whenever there are any isochronous USB audio streams happening. I know there is a Windows Hotfix supposed to be available to target exactly this problem - https://support.microsoft.com/en-us/kb/981214 - but the Hotfix refuses to install, presumably because the Hotfix itself is quite old and does not seem to recognize newer versions of usb*.sys drivers on any up-to-date instance of Windows 7.
The M6700 has EHCI and xHCI controllers routed to different physical ports; it might be worth noting that the problem appears identical regardless of whether the audio interface (a Focusrite Scarlett 18i20) is connected to EHCI or xHCI. All possible causes other than usbport.sys have been eliminated by careful configuration and measurement, i.e. there is no CPU throttling, no CPU turbo, no CPU C-states, no HyperThreading, no Power Management events, no Virtual Memory Paging, even no SMI's (System Management Interrupts) going on, it all boils down to usbport.sys hogging the CPU.
It might also be worth noting that according to Intel, there are a bunch of known USB Host Controller bugs in 7-series / C216 chipsets, one can find a detailed Errata section starting from page 15 of the Spec Update document - http://www.intel.com/content/***/www/public/us/en/documents/specification-updates/7-series-chipset-pch-spec-update.pdf
Could this CPU hogging problem actually stem from bugs in the USB host controller hardware driving the OS driver nuts? Or does it stem from an unrelated bug in the OS driver? And what happened to the existing Windows Hotfix, why does it refuse to install on up-to-date OS and how come the same old problem suddenly re-appeared on automatically updated Windows 7 systems?
In any event, it is my sincerest and most humble hope as a paying customer, for an updated Hotfixto address this problem if at all possible, one that actually agrees to install itself. Without a working fix, the otherwise excellent Dell Precision M6700 Mobile Workstation is quite useless for any serious audio work due to CPU hogging and audio dropouts, just because the USB subsystem is coughing up (be it hardware bug or driver bug or combination of both).
I'm also finding it difficult to forget that the Precision Mobile Workstation line has actually been advertised, by Dell, to be an excellent choice for professional audio applications, and the effect said advertisement had on my purchasing decision. True story - https://www.youtube.com/watch?v=B0tbhz65JRw - Ironic.