Andrei Frumusanu (andrei.delete@this.anandtech.com) on August 17, 2018 10:36 am wrote:

>
> Again you're using the argument of a non-power optimised development board, using
> higher frequencies than used in mobile, in open-air or cooler if you chose to,
> using broken drivers in a use-case where the true power would be 1/50th.
>
> Like what exactly is your point here? Again we can go break any "15W" Intel chip and
> make it use 35W. Does it mean anything? No, it's just random numbers thrown around.



I am sorry, but for the second time, what you reply has no relationship with what I have written.

It was not using higher frequencies than in mobile, but the same up to 2.0 GHz clock frequency used in the smartphones with that Exynos. I do not even know if it is possible to overclock these ARM processors. I have never tried that, as even the nominal frequency was hardly attainable without improved cooling.

"Broken drivers" has absolutely no relevance, as I was talking about a custom ARM program which did not need any drivers, as it was run on the CPU. It is not relevant that with other drivers we could have used a hardware implementation which uses less power. We were discussing the power consumption of the ARM cores.


I was giving a real example where a simple program, which was doing an useful function and which was not designed to maximally exercise the processor, was nonetheless raising the power consumption much above the values claimed in the ARM presentations.

IIRC the value claimed by ARM for Cortex-A15 was 1.5 W per core, but my simple program raised the power consumption to a double value.

You may claim that this was Samsung's fault, maybe they botched the physical implementation of the good ARM design, but I doubt it.

Among other things, I design boards using ARM processors and almost all of them have over-optimistic power consumption values.


I have a couple of Qualcomm SDM845 now and I intend to do a more thorough power consumption measurement on them to see if this time the ARM claims are real. Unfortunately, I did not have time to do it until now and I will probably not do it before next month.


And you cannot "break" an Intel chip, unless you raise the power limits in the appropriate MSR's.

If you set both the long term and the short term power limits to 15 W, then the Intel processor will never exceed the 15 W power consumption. If you set the power limit to 35 W, only then it will happily use 35 W until it overheats and the thermal protection throttles it.

I have never tested Y processors, so I do not know how they behave. But for all the processors with TDP of 15 W or higher that I have ever tested, the single core turbo frequency was never high enough so that the power consumption could reach the TDP, regardless what program you were executing.

So if an Intel processor is specified for 3.5 GHz turbo, you can be reasonably certain that any single-core program will run at 3.5 GHz.


On the other hand, if you have an ARM processor that is claimed to have a 2.0 GHz clock frequency (without any "turbo" mention) then you can be reasonably certain that it will never be able to run any interesting program at 2.0 GHz without overheating, except for very short times.


Like I have said, I have not tested yet SDM845, to see if can really run anything at 2.8 GHz. Maybe it can, because of the modern process used for its fabrication.

All the ARM processors that I have tested and which never lived up to their promises from the power consumption POV were in 28 nm or in older processes, because the more recent processors, e.g. Snapdragon 835 or 845, have prices similar to Intel, so they are too expensive for embedded use.

Maybe these newer processors are better and they consume the power claimed in the ARM presentations, but I have not seen yet any information to support this conclusively.