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[Anandtech] More Phenom bugs apparently

post #1 of 8
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Link to Page 4(the nitty gritty

Page 1 Link to whole article

Quote:
We talked about how it's possible that threads moving between these different cores, needing to wake the next one up rather than running on an already at speed core, could possibly impact performance. As the Phenom is the only CPU architecture we currently have access to with individual PLLs per core (Intel's CPUs must run all cores at the same frequency), the CnQ issues could be related to that.
I suggest the AMD guys read this because there seems to be some major problems.

Basically, with vista, it swaps threads around on the cores even though they might not be finished, so instead of finishing a video encoding on one core and burning a DVD using another, it is continuously switching the workload around on all 4 cores.

Quote:
Our minds then wandered over to what we saw when we looked at the AMD Power Meter. Since Windows Vista takes it upon itself to move threads between cores in fairly stupid ways, during the Photoshop test we saw what looked like threads bouncing around between cores or cycling through them in rapid succession. Whatever was actually being done, the result was that one processor would ramp up to full power (1GHz up to 2GHz) and then drop back down as the next CPU came up to speed.
Quote:
There has to be a factor that is AMD specific that causes this problem -- and not only that but Phenom specific because we've never seen this problem on other AMD parts.

Or have we?

AMD GPUs last year exhibited quite an interesting issue with their power management features that were clearly evident in specific locations while playing Crysis. The culprit was the dynamic clocking of the GPU based on the graphics load. Because the hardware was able to switch quickly between modes, and due to the way Crytek's engine works, AMD GPUs were constantly speeding up and slowing down in situations where they should have been at full speed the entire time.
Basically, if you have vista and a phenom, disable Cool N Quite, but. . .

Quote:
The Phenom’s flaky Cool'n'Quiet performance in some of our benchmarks forced us to test with it disabled, unfortunately with it disabled we ran into another problem: stability.
Besides all this, it still seems like the phenom is getting screwed over by the mobo manufacturer's in the OC dept.
Edited by joemaniaci - 7/2/08 at 9:35pm
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post #2 of 8
Who runs with CnQ on around here? And they are using the 780g chipset, which means that they decided to overclock a motherboard with integrated graphics. Has an effect on the landscape.

Now if the new 790 boards end up having these same issues it will be a problem. Also if the 9950 still won't beat a Q6600 after a full calendar year and some change then AMD still looses when my it comes time for my next system build.
Edited by Jarhead - 7/2/08 at 10:16pm
post #3 of 8
Kinda seems like some of the power management features are hurting the performance of AMD's stuff. I hope they can get this all sorted out so if the sb750 rumors are true that release can go off well.
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post #4 of 8
Does AMD make some assertion that using C&Q will result in the same performance as having it turned off?

I doubt it.

Does switching from core to core while running one thread cause a loss of performance, almost certainly.

I fail to see the mystery. The only question here is whether the switching between cores is intentional.

Whatever the case it's named "Cool & Quiet" for a reason... If you want power it's going to make Heat and Noise!!!

I will say that I've experienced the lower performance with C&Q on, and when I know I'm going to do something that I need 100% performance for, It's just a quick stop in power management to switch to a different power scheme.
Edited by AMDorElse - 7/2/08 at 10:21pm
    
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post #5 of 8
Well C&Q really has no place on a site like OCN. I understand some people want energy saving PC's but that is not our business here.

I would like to see a better performing chip with lower watts...only because I want to OC the heck out it.
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post #6 of 8
Hmm. My 780G clocks pretty well (CPU is at 2.8ghz just from bumping up the multiplier) and I don't have any stability problems. C&Q is disabled as well.
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post #7 of 8
I use C'nQ sometimes... and OC without C'nQ obviously. In my home there are many rigs, some of them use C'nQ to keep a lower power consumption.

It is a feature we're paying for, it will be good if would actually work. It looks more like a vista/driver related issue anyway, the chip DOES NOT transfer threads, the software does.
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post #8 of 8
Cool and Quiet is an enviro-fad technique that belongs in laptops. I've turned it off on every AMD PC I've had.
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