Strange USB-Audio streaming behaviour of DPC

I am running up to 6 USB audio devices (8bit 8khz sampling rate) in parallel
and I have observed on my computer, that DPC starts with a CPU load of 35-50%
and after 2 minutes the CPU load decreases down to 0%.

However, sometimes the DPC pulses in the following way:
* 5 seconds no CPU load
* 3 seconds 20-30% CPU load.

I am not sure what could cause such an effect and until now I have tried
different configurations without a hint. However, the USB host controller
should not be a bottleneck. I have a load of less than 5% of total USB
bandwidth.

Environment:
* Windows 7 64bit
* HP xw4600 workstation
* up to 6 USB audio devices connected over a hub

Can anyone gives me hint?
g
michael

Sounds similar to this issue (hotfix available):

http://support.microsoft.com/kb/981214

MichaelS wrote:
> I am running up to 6 USB audio devices (8bit 8khz sampling rate) in parallel
> and I have observed on my computer, that DPC starts with a CPU load of 35-50%
> and after 2 minutes the CPU load decreases down to 0%.
>
> However, sometimes the DPC pulses in the following way:
> * 5 seconds no CPU load
> * 3 seconds 20-30% CPU load.
>
> I am not sure what could cause such an effect and until now I have tried
> different configurations without a hint. However, the USB host controller
> should not be a bottleneck. I have a load of less than 5% of total USB
> bandwidth.
>
> Environment:
> * Windows 7 64bit
> * HP xw4600 workstation
> * up to 6 USB audio devices connected over a hub
>
> Can anyone gives me hint?
> g
> michael

Tests have been successful. Now, I cannot observe the DPC pulse.

However, after initiating streaming the DPC starts with a constant CPU load
of 20-30% and decreases after 2 minutes.
g
Michael

Thanks for the hint. I will install the hotfix.
However, most of the audio devices are USB1.1 devices which are connected to
a USB 2.0 MTT capable hub.
g
Michael

"Philip Ries [MSFT]" wrote:

> Sounds similar to this issue (hotfix available):
>
> http://support.microsoft.com/kb/981214
>
> MichaelS wrote:
> > I am running up to 6 USB audio devices (8bit 8khz sampling rate) in parallel
> > and I have observed on my computer, that DPC starts with a CPU load of 35-50%
> > and after 2 minutes the CPU load decreases down to 0%.
> >
> > However, sometimes the DPC pulses in the following way:
> > * 5 seconds no CPU load
> > * 3 seconds 20-30% CPU load.
> >
> > I am not sure what could cause such an effect and until now I have tried
> > different configurations without a hint. However, the USB host controller
> > should not be a bottleneck. I have a load of less than 5% of total USB
> > bandwidth.
> >
> > Environment:
> > * Windows 7 64bit
> > * HP xw4600 workstation
> > * up to 6 USB audio devices connected over a hub
> >
> > Can anyone gives me hint?
> > g
> > michael
> .
>