I'm running BOINC version 6.4.5 on an Intel Q6600 Quad processor CPU with an NVIDIA GeForce 8800 GTX GPU. Right now I have one Astropulse 5.00 WU, one SETI@home Enhanced 6.08(cuda) WU amd two MilkyWay@home 0.19 WUs crunching.
Using Process Explorer, I see the three non-cuda WUs all running at about 25% (full utilization of 3 out of 4 CPUs). The fourth CPU, working on the cuda WU, is running at about 0.4%. Meanwhile I am seeing explorer.exe jumping around between 0.3% and 20 %. When explorer.exe gets up above about 2%, the cuda WU goes to 0%. As noted by others at SETI@home, other apps are extremely slow when running BOINC.

Suspending the MilkyWa@home does not improve the situation. Exiting AVG and Spyware Terminator doesn't help either.

The following seems to help for a while. Suspend the cuda WU, which allows a MilkyWay@home WU to start up. Now resume the cuda WU and suspend one of the MilkyWay@home WUs. The cuda WU now runs at 1% to 5% and explorer.exe is between 0% and 1%. This is how things used to work. I'm not sure when the change ocurred.

This lasts until the cuda WU has finished and a new cuda WU starts up. The situation now reverts back to where it was at the start of this post. The cuda WU is running 0% to 0.3% and explorer.exe is 0.3% to 20%. Other apps have slowed to a crawl.

I hope there is some information in this post that will help diagnose the problem.

When the thread at Seti started, I asked the development team about this. They told me that the CUDA application does not use explorer.exe in any way, so it must be something on your computer that does this.

Think about indexing programs, search programs and the extensions option.
It's probably a good idea to check with FileMon and Process Explorer what is happening on your system.

(I'll post the same info in that thread)

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This morning, explorer.exe seems to be behaving itself. I see it between 0% and 0.4% for a second or so about every 10 seconds. The cuda WU is ticking along at 1.5% to 3.4% with occasional excursions to 5%.

I have had the indexing service completely disabled on my computer for several months now. With a fully expanded process tree, I can see two or three other processes popping in and out that each use no more than 0.4%. The System Idle Process fluctuates between 18% and 23%.

If explorer.exe starts to act up again, I will monitor what other processes are running and post a question.

Thanks for your help.

If explorer.exe starts to act up again, I will monitor what other processes are running and post a question...

Also check the type of the CUDA task (angle range!).