two GPU's fighting over CPU resources

[sluggo]

I configured an older socket 939 SLI board today with an 8600GT and an 8400GS. Unfortunately, according to procexp, the two are using the same core of an Opteron and it's really slowed the 8600. One of the Opteron's cores is at 100% utilization and the other is at 0%. Both of my GPU2 clients are configured to NOT lock to a specific core. I assumed that meant that both CPU cores would be utilized as necessary, but that does not appear to be the case.

Can somone clear this up for me please? And how would I force/allow the other core to be used?

[Usacomp2k3]

What OS? Sounds like a scheduling problem.

[Flying Fox]

What OS? Sounds like a scheduling problem.

Not quite, because in theory a process with no affinity set should be run on different cores (otherwise the scheduler will be really buggy). For some reason the GPU2 client processes seem to want to stick with 1 core.

The simplest (but need manual work) is to just bring up Task Manager and force the 2 FaHCore_*.exe to go their separate cores, but you have to do it everytime a new WU is being worked on. I believe they have options to set affinity in the GPU2 client.

[jeffry55]

I configured an older socket 939 SLI board today with an 8600GT and an 8400GS. Unfortunately, according to procexp, the two are using the same core of an Opteron and it's really slowed the 8600. One of the Opteron's cores is at 100% utilization and the other is at 0%. Both of my GPU2 clients are configured to NOT lock to a specific core. I assumed that meant that both CPU cores would be utilized as necessary, but that does not appear to be the case.

Can somone clear this up for me please? And how would I force/allow the other core to be used?

You can set CPU affinity in Task Manager in XP & Vista. Right click on the taskbar, select Task Manager, right click on Fahcore11.exe and set CPU affinity by checking or unchecking the desired cpu box.

There are also some links in this thread on setting up two instances of the GPU client and setting core affinity in the GPU client.

Hope this helps.

[sluggo]

Thanks all for the tips.

This is a Windows XP machine. Resetting the affinities in task manager worked to open up the other core. The GPU clients were both set to run on CPU1 so I set them both to run on both CPUs. Now I have both cores runnning at 100% utilization but, curiously, not much of an improvement in GPU throughput.

This was puzzling - I would not have thought that the two clients would completely swamp the Opteron. I paused one of the clients and the CPU utilization dropped to exactly 50%, spread across the two cores. I resumed the first core, CPU utilization went back to 100%, and then I paused the other core. CPU dropped to exactly 50% again, spread across the two cores.

I don't know how to interpret these results. Is there something in the client code that restricts it to no more than 50% loading, regardless of it's need?

Right now I'm testing the stability of a 25% overclock on the processor. Then I'll run the clients again to see if the utilization percentages change. After that, maybe I'll underclock the GPUs.

[Flying Fox]

It's a quirk in Task Manager. 100% of 1 core out of 2 total cores is 50% "overall". You should look at the CPU usage graph and you will see at any give point one core is getting maxed out.