Trying The Configurable 45 Watt TDP With AMD's A10-7800 / A6-7400K

[phoronix]

Phoronix: Trying The Configurable 45 Watt TDP With AMD's A10-7800 / A6-7400K

AMD Kaveri APUs feature a configurable TDP whereby users can opt to run their A-Series APUs with a lower power consumption and operating temperature but at the cost of slightly reduced performance.

http://www.phoronix.com/vr.php?view=20764

[Ilfirin]

Power measurement

I think, it would be handy, if you could include some more real tests over time. For example "total power consumtion on: idling 5 minutes, compiling kernel, some graphics bechmark and again idling (different times to finish at same time)"

[schmidtbag]

While the option is nice, I feel like the need for this is pretty rare. If someone were to consistently lower the performance like this, they're better off just buying an A8 or maybe even an A6.

[GraysonPeddie]

CPU temperatures in benchmarks would be nice, but then the 45w configurable TDP would probably be worthless.

[Michael]

CPU temperatures in benchmarks would be nice, but then the 45w configurable TDP would probably be worthless.

The CPU thermal monitoring doesn't work quite right for those APUs, as explained in other article.

[oleid]

performance per watt numbers are wrong?

I'm not sure these Performance/Watt values make sense in every case. While perf/Watt is better for 45W TPD (although you write: Xonotic was also more power efficient with the stock TDP.), it's worse for the benchmarks you measure the time to complete the task. I'm not even sure how you get "perf/Watt" for the "Linux kernel" and the "c-ray" benchmark.

Naively, I'd do the following: To calculate something proportional to "performance", I'd take the inverse time ( N Operations take m seconds, therefore the performance is N/m). As I don't know the number of operations, I'll leave N=1. Thus, performance per watt is:

Linux kernel:

stock: S = 1 OP/(163.81s * 111.8W) ~ 5.46e-5 OP/s / W
45W : T = 1 OP/(183.27s * 93.6W) ~ 5.83e-5 OP/s / W

Or normalized to stock: T / S ~ 1.07

C-Ray:

stock: S = 1 OP/(58.64s * 109.1W) ~ 1.56e-4 OP/s / W
45W : T = 1 OP/(66.73s * 91.5W) ~ 1.64e-4 OP/s / W

Or normalized to stock: T / S ~ 1.05

Thus, performance per watt is in any case worse for the stock tuning.

[oleid]

.... except the valley benchmark of curse! But that's not playable anyway

[moony]

Thus, performance per watt is in any case worse for the stock tuning.

I fully agree with oleid; the task is to compile the Linux kernel:

Stock TDP: 163.81 seconds * 105.5 W = 4.80 Wh
45W TDP: 183.27 seconds * 87.9 W = 4.47 Wh

So for one task (compiling the kernel), the 45W TDP setting uses less watts per hour, therefore it's more efficient!

[devius]

I'm not sure these Performance/Watt values make sense in every case.

They don't. People have been complaining that the formulas used for performance/watt are incorrect and return completely stupid and wrong values since the very first article of this kind was published some 2 years ago, but Michael just doesn't care, and prefers to have useless articles with wrong data and conclusions, since that probably makes him more money. At least people are commenting on the forums that the calculations are wrong, where if they weren't wrong, people would only have valid data to talk about. Who wants that, right?

There was even this case in one of the articles that was soooo obvious and yet he published the damn thing. It was like a cpu was consuming double the energy of another one while only providing some 10% increase in performance and the cpu with the higher energy consumption was deemed as the most efficient. Seriously... don't waste your time. It will never be fixed.

[smitty3268]

There was even this case in one of the articles that was soooo obvious and yet he published the damn thing. It was like a cpu was consuming double the energy of another one while only providing some 10% increase in performance and the cpu with the higher energy consumption was deemed as the most efficient. Seriously... don't waste your time. It will never be fixed.

Yeah, i remember that and thinking "how the hell does michael think this makes any sense at all"?