Two ATI 7750s, Count 0.5, Four Active Tasks, Only Two Progressing?

Hello,

I just put a couple of ATI 7750's (1MB memory) into an older ATI motherboard that happened to have two PCIE-2.0 slots running at 8x / 8x. The processor is an anemic Athlon 64x2, though upgradeable all the way to a PhenomII x6 if I so chose.

I'm using the Lunatics apps and have my COUNT set to 0.5. BOINC is showing four active tasks at a time, two per GPU, but only two progress at any one time, sometimes one from each card, sometimes both on the same card - the other two tasks just burn up time, but % complete doesn't move at all. I am not running CPU tasks. GPU-Z shows about 85% card utilization, which would normally mean I can run a second unit per card.

Any idea what's going on, why all four units do not progress at the same time? I thought I could get away with this configuration despite the slow 2-core CPU, but I don't know if this is indicative of a CPU throttle, or if it means these low-end cards can really only do one work unit at a time (unlikely since sometimes the WUs that are progressing are both on the same card) or if I'm doing something else stupid.

Thanks for any assistance.

EDIT: drivers are the latest, but I just noticed the cards are showing up as "unknown" in my computers list.
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There is a mysterious bug related to cpu/gpu communication latency whose symptoms are just what you have.

The oft-mentioned kludge is to idle a core for every gpu job. You obviously can't do that for, er, obvious reasons.

As an experiment try setting the priority of the running processes (all four of them) to above normal or high and see what happens.

Oh, I assume you don't run any cpu tasks at the same time? I saw you aborted some.

Edit: Also try setting all 4 tasks to run on the same core. I know it's counter-intuitive but...just try.

<cmdline>-period_iterations_num 20 -instances_per_device 2</cmdline>
<coproc>
<type>ATI</type>
<count>0.5</count>
</coproc>


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- ALF - "Find out what you don't do well ..... then don't do it!" :)

Thank you, trying these things now. Just discovered that the second card drops me to 1.1 PCI-e 8x on both slots (one card gets 16x 2.0, two gets 1.1 8x each) if that affects anything.

I'm not running CPU tasks; those aborts are probably from previous mucking about with the machine.

Back in a bit.

EDIT: Changing instances per device to 2 did the trick. Benchmarking now to see if this is the best use of the system.

I think I'm swearing off of cheap DDR-2 systems on Craig's List.
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Benchmarking now to see if this is the best use of the system.