The ARM vs x86 Wars Have Begun: In-Depth Power Analysis of Atom, Krait & Cortex A15
by Anand Lal Shimpi on January 4, 2013 7:32 AM EST- Posted in
- Tablets
- Intel
- Samsung
- Arm
- Cortex A15
- Smartphones
- Mobile
- SoCs
Determining the TDP of Exynos 5 Dual
Throughout all of our Cortex A15 testing we kept bumping into that 4W ceiling with both the CPU and GPU - but we rarely saw both blocks use that much power at the same time. Intel actually tipped me off to this test to find out what happens if we try and force both the CPU and GPU to run at max performance at the same time. The graph below is divided into five distinct sections, denoted by colored bars above the sections. On this chart I have individual lines for GPU power consumption (green), CPU power consumption (blue) and total platform power consumption, including display, measured at the battery (red).
In the first section (yellow), we begin playing Modern Combat 3 - a GPU intensive first person shooter. GPU power consumption is just shy of 4W, while CPU power consumption remains below 1W. After about a minute of play we switch away from MC3 and you can see both CPU and GPU power consumption drop considerably. In the next section (orange), we fire up a multithreaded instance of CoreMark - a small CPU benchmark - and allow it to loop indefinitely. CPU power draw peaks at just over 4W, while GPU power consumption is understandably very low.
Next, while CoreMark is still running on both cores, we switch back to Modern Combat 3 (pink section of the graph). GPU voltage ramps way up, power consumption is around 4W, but note what happens to CPU power consumption. The CPU cores step down to a much lower voltage/frequency for the background task (~800MHz from 1.7GHz). Total SoC TDP jumps above 4W but the power controller quickly responds by reducing CPU voltage/frequency in order to keep things under control at ~4W. To confirm that CoreMark is still running, we then switch back to the benchmark (blue segment) and you see CPU performance ramps up as GPU performance winds down. Finally we switch back to MC3, combined CPU + GPU power is around 8W for a short period of time before the CPU is throttled.
Now this is a fairy contrived scenario, but it's necessary to understand the behavior of the Exynos 5250. The SoC is allowed to reach 8W, making that its max TDP by conventional definitions, but seems to strive for around 4W as its typical power under load. Why are these two numbers important? With Haswell, Intel has demonstrated interest (and ability) to deliver a part with an 8W TDP. In practice, Intel would need to deliver about half that to really fit into a device like the Nexus 10 but all of the sudden it seems a lot more feasible. Samsung hits 4W by throttling its CPU cores when both the CPU and GPU subsystems are being taxed, I wonder what an 8W Haswell would look like in a similar situation...
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kumar0us - Friday, January 4, 2013 - link
My point was that for a CPU benchmark say Sunspider, the code generated by x86 compilers would be better than ARM compilers.Could better compilers available for x86 platform be a (partial) reason for faster performance of intel. Or compilers for ARM platform are mature and fast enough that this angle could be discarded?
iwod - Friday, January 4, 2013 - link
Yes, not just compiler but general optimization in software on x86. Which is giving some advantage on Intel's side. However with the recent surge of ARM platform and software running on it my ( wild ) guess is that this is less then 5% in the best case scenario. And it is only the worst case, or individual cases like SunSpider not running fully well.jwcalla - Friday, January 4, 2013 - link
Yes. And it was a breath of fresh air to see Anand mention that in the article.Look at, e.g., the difference in SunSpider benchmarks between the iPad and Nexus 10. Completely different compilers and completely different software. As the SunSpider website indicates, the benchmark is designed to compare browsers on the same system, not across different systems.
monstercameron - Friday, January 4, 2013 - link
it would be interesting to throw an amd system into the benchmarking, maybe the current z-01 or the upcoming z-60...silverblue - Friday, January 4, 2013 - link
AMD has thrown a hefty GPU on die, which, coupled with the 40nm process, isn't going to help with power consumption whatsoever. The FCH is also separate as opposed to being on-die, and AMD tablets seem to be thicker than the competition.AMD really needs Jaguar and its derivatives and now. A dual core model with a simple 40-shader GPU might be a competitive part, though I'm always hearing about the top-end models which really aren't aimed at this market. Perhaps AMD will use some common sense and go for small, volume parts over the larger, higher performance offerings, and actually get themselves into this market.
BenSkywalker - Friday, January 4, 2013 - link
There is an AMD design in their, Qualcomm's part.A D R E N O
R A D E O N
Not a coincidence, Qualcomm bought AMD's ultra portable division off from them for $65 million a few years back.
Anand- If this is supposed to be a CPU comparison, why go overboard with the terrible browser benchmarks? Based on numbers you have provided, Tegra 3 as a generic example is 100% faster under Android then WinRT depending on the bench you are running. If this was an article about how the OSs handle power tasks I would say that is reasonable, but given that you are presenting this as a processor architecture article I would think that you would want to use the OS that works best with each platform.
powerarmour - Friday, January 4, 2013 - link
Agreed, those browser benchmarks seem a pretty poor way to test general CPU performance, in fact browser benchmarks in general just test how optimized a particular browser is on a particular OS mainly.In fact I can beat most of those results with a lowly dual-A9 Galaxy Nexus smartphone running Android 4.2.1!
Pino - Friday, January 4, 2013 - link
I remember AMD having a dual core APU (Ontario) with a 9W TDP, on a 40nm process, back in 2010.They should invest on a SOC
kyuu - Friday, January 4, 2013 - link
That's what Temash is going to be. They just need to get it on the market and into products sooner rather than later.jemima puddle-duck - Friday, January 4, 2013 - link
Impressive though all this engineering is, in the real world what is the unique selling point for this? Normal people (not solipsistic geeks) don't care what's inside their phone, and the promise of their new phone being slighty faster than another phone is irrelevant. And for manufacturers, why ditch decades of ARM knowledge to lock yourself into one supplier. The only differentiator is cost, and I don't see Intel undercutting ARM any time soon.The only metric that matters is whether normal human beings get any value from it. This just seems like (indirect) marketing by Intel for a chip that has no raison d'etre. I'm hearing lots of "What" here, but no "Why". This is the analysis I'm interested in.
All that said, great article :)