There is a related known issue in Win7, with a hotfix available:
http://support.microsoft.com/kb/981214
Franz Detro wrote:
Hi,
> Have you tried disabling other hardware? Especially network adapter
> driver turn out to be source for DPC holidays.yes. I’ve tried to disable network, inboard sound cards, even unused internal USB hubs, no difference.
> Other than that there
> are a some measurement tools indicating DPC caused latency issues you
> can use to find the assaulting driver.I’ve used the Thesycon DPC latency checker, which does not show any spikes.
I did traces with the Windows 7 Performance Analyzer, which points me to USBPORT.SYS::USBPORT_Xdpc_Worker.
80 % of the calls are spending max. 0.066 ms there (20 % only 0.007 ms), but the remaining 20 % do spend up to 0.253 ms there. One remarkable thing is that there is a ‘gap’ in the samples between 0.066 ms and 0.105 ms. In other words: it looks like there is some special condition which causes the DPC to use 2 - 5 times more CPU than the ‘maximal standard case’.
All my analysis points to a problem with the Windows 7 / Vista implementation of USBPORT.SYS.
> Best,
> Hagen.
>Best,
Franz