CPU blocking GPU ???

[Pizzadude]

I have just come across a strange anomaly on my system. First my setup is as follows I7 920 @ 3.6ghz, 12gb of triple channel ddr3, 2 x GTX460 with moderate overclock and 850w power supply. Now usually I run 4 CPU work units and 4 cuda work units (2 per GPU), giving  a total of 8 units in process at any one time. Now as my I7 has hyperthreading I upped my CPU usage to 6 work units and within two minutes I noticed my GPU temperatures starting to drop.  It would appear that my 2 GPU's are now taking 20% to 30% slower.  If I reduce the CPU back to 4 units the GPU's return to normal temperatures and throughput.

Any thoughts ?

[skildude]

hyperthreading is running 2 CPU WU's per CPU.  Plus you are trying to run an additional 4 WU's through those same cores.  You've basically choked your CPU's so that the GPU's can't lbe loaded because the CPU's are maxed out.

[Pizzadude]

CPU utilization is only showing as 70% whilst the processing the 6 CPU WU and 4 GPU WU and yet something is holding the GPU back.

CPU useage increases to 100% momentarily when new units are fed to the GPU after one has completed.

[skildude]

I tried doing a search on Seti.  I've found several instances that support what I've mentioned . Using hyperthreading and GPU will cause problems on the GPU.  I bet its even worse when you run multiple instances on the GPU

[Pizzadude]

Boinc Version 6.12.14 (X64) Beta  seem to go some way to easing this problem and so far seems stable.