That's total energy which isn't what this article is testing exactly. Increasing time and lowering power would give the same total energy but would you actually prefer that? If so, then there are ARM and Atom chips that might give the same total energy.
I want 1/time/energy which could also be converted to 1/time/(average power) to get performance per Watt.
Last edited by jwilliams; 01-18-2014 at 02:43 PM.
Also, one way of measuring performance is in operations per second. Watts are equal to Joules per second. So we can write:
Note that by operations I am talking about a generalized, high-level kind of operation, not a CPU instruction. So the number of operations is the same for a given compilation, independent of the CPU. So we can ignore "operations" in the above formula and only look at the energy usage in Joules. Which is just what tuke81 showed us.Code:Performance per Watt = ( operations / second ) / ( Joule / second ) = operations / Joule
Again, good job tuke81 !
It would be really interesting to run those tests with Kaveri at 45W and 65W, says the AMD guy
If the graphics performance scales comparably to Windows benchmarks then a back-of-envelope calculation suggests that the FPS/W numbers on Tropics would end up around 0.17 (15.7 fps / 94.8 w) at 65W and 0.19 (13.9 fps / 74.8W) at 45W, but I haven't actually run the tests and my 2-core low clock 1-stick-of-RAM Kaveri engineering box would not be a particularly good test bed.
The interesting thing is that in the lower power settings the biggest hit from 95/100W to 45W is only about 25% (GPU shader & texturing), CPU hit is maybe 17%, and AFAICS the ROP-limited GPU functions don't drop at all because the # of CUs is reduced from 8 to 6 but the # ROPs and GPU clock seem to be unchanged.
Last edited by bridgman; 01-18-2014 at 03:00 PM.
I have no numbers about my ARM/Atom statement. It was just to emphasize that total energy isn't the whole picture. I concede that knowing what the work load is related to that total energy is useful. Maybe Michael can run ARM and Atom tests to see how much energy is used for the same workload.Yes, total energy required to perform a computation is a reasonable thing to be concerned about if your computer can be powered off or powered down (i.e., sleep or hibernation) into a low power state after the computation is done. And I doubt there are computers with an ARM CPU that can do the same computation for less total energy than a computer with an i7 haswell CPU (remember that it is not just the CPU that requires power during the computation).
That's why I said converted to get a performance per Watt number. However, I can see how my wording can be confused to be seen as equal.
I still prefer performance/Watt or operations/Joule over total energy per work load.
Last edited by vick; 01-18-2014 at 03:23 PM.
I still say that for some cases energy/work load can mislead people if the energy saved was at a cost of longer than desired time or performance.
Do you have numbers for energy/work load on recent Atom chips? Maybe there's a Phoronix article somewhere.