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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kyuu - Friday, January 4, 2013 - link
You're the one stepping into the past with the CISC vs. RISC. x86 is not going to go away anytime soon. Keep dreaming, though.iwod - Saturday, January 5, 2013 - link
Nothing about Architectures in this comment, but by the time ARM Cortex A57 is out, so is Intel ValleyView, which doubles the performance. A57 is expected to give in best case scenario 30 - 50% increase in performance. And All of a sudden this look so similar to 2x Atom performance.It will only take one, just ONE mistake that ARM make for Intel to possibly wipe them off the map.
Although looking into the next 3 - 5 years ahead. It will be a bloody battle instead.
Cold Fussion - Friday, January 4, 2013 - link
Why didn't have any charts which were performance per watt or energy consumption vs performance in the GPU area? If the Mali chip is using twice the energy but giving 3x the performance then that is a very significant point thats being misrepresented.mrdude - Friday, January 4, 2013 - link
I was thinking the same thing.If I can game at native resolution on a Nexus 10 at better frame rates than on the Atom or Snapdragon SoC and the battery capacity is larger and the price of the device is equal, then do I really care about the battery life?
Although it's nice seeing Intel is getting x86 down to a competitive level with ARM, the most astonishing thing that I took away from that review was just how amazing that MaliT604 GPU is. All that performance and only that power draw? Yesplz :P
parkpy - Friday, January 4, 2013 - link
i've learned so much from AT's review of the iPhone5, Galaxy S III, and Nexus 4, and this article about mobile phones that it makes me wish AT could produce MORE reviews of mobile devices.All of this information is crack! I can't get enough of it. Keep up the good work! And Intel, I can't wait for you to get your baseband processor situation sorted out!
I was already tempted to get a Razr I, but it looks like before the end of the year consumers will have some very awesome technology in their phones that won't require as much time on the battery charger!
This Guy - Friday, January 4, 2013 - link
What if Rosepoint is software defined instead of fixed function?ddriver - Friday, January 4, 2013 - link
I am confused here - this review shows the atom to be somewhat faster than A15, while the review at phoronix shows the A15 destroying the atom, despite the fact intel's compiler is incredibly good at optimizations and incomparably more mature.So I am in a dilemma on who to trust - a website that is known to be generously sponsored by intel or a website that is heavily focused on open source.
What do you think?
kyuu - Friday, January 4, 2013 - link
Uh, did we read the same article? Where does it show the Atom being "somewhat faster than A15"? The article showed that the A15 is faster than Atom, but at a large power premium.ddriver - Friday, January 4, 2013 - link
On the charts I see the blue line ending its task first and taking less time, blue is atom, right?jwcalla - Friday, January 4, 2013 - link
A couple things:1) The Phoronix benchmarks were for different Atoms than the one used in this article. I don't know how they compare, but they're probably older models.
2) The Phoronix benchmarks used GCC 4.6 across the board. Yes, in general GCC will have better optimizations for x86, but we don't know anything (unless I missed it) about which compilers were used here. If this was an Intel sample sent to Anand, I'm sure they compiled the software stack with one of their own proprietary Intel compilers. Or perhaps it is the MS compiler, which no doubt has decades of x86 optimizations built in and probably less ARM work than GCC (for the RT comparison).
Don't take the benchmarks too seriously, especially since even the software isn't held constant here like it was in the Phoronix benchmarks. It's all ballpark information. Atom is competitive with ARMv7 architectures -- that's the takeaway.