Power Consumption

There's a lot of uncertainty around whether or not Kepler is suitable for ultra low power operation, especially given that we've only seen it in relatively high TDP (compared to tablets/smartphones) PCs. NVIDIA hoped to put those concerns to rest with a quick GLBenchmark 2.7 demo at Siggraph. The demo pitted an iPad 4 against a Logan development platform, with Logan's Kepler GPU clocked low enough to equal the performance of the iPad 4. The low clock speed does put Kepler at an advantage as it can run at a lower voltage as well, so the comparison is definitely one you'd expect NVIDIA to win. 

Unlike Tegra 3, Logan includes a single voltage rail that feeds just the GPU. NVIDIA instrumented this voltage rail and measured power consumption while running the offscreen 1080p T-Rex HD test in GLB2.7. Isolating GPU power alone, NVIDIA measured around 900mW for Logan's Kepler implementation running at iPad 4 performance levels (potentially as little as 1/5 of Logan's peak performance). NVIDIA also attempted to find and isolate the GPU power rail going into Apple's A6X (using a similar approach to what we documented here), and came up with an average GPU power value of around 2.6W. 

I won't focus too much on the GPU power comparison as I don't know what else (if anything) Apple hangs off of its GPU power rail, but the most important takeaway here is that Kepler seems capable of scaling down to below 1W. In reality NVIDIA wouldn't ship Logan with a < 1W Kepler implementation, so we'll likely see higher performance (and power consumption) in shipping devices. If these numbers are believable, you could see roughly 2x the performance of an iPad 4 in a Logan based smartphone, and 4 - 5x the performance of an iPad 4 in a Logan tablet - in as little as 12 months from now if NVIDIA can ship this thing on time.

If NVIDIA's A6X power comparison is truly apples-to-apples, then it would be a huge testament to the power efficiency of NVIDIA's mobile Kepler architecture. Given the recent announcement of NVIDIA's willingness to license Kepler IP to any company who wants it, this demo seems very well planned. 

NVIDIA did some work to make Kepler suitable for low power, but it's my understanding that the underlying architecture isn't vastly different from what we have in notebooks and desktops today. Mobile Kepler retains all of the graphics features as its bigger counterparts, although I'm guessing things like FP64 CUDA cores are gone.

Final Words

For the past couple of years we've been talking about a point in the future when it'll be possible to start playing console class games (Xbox 360/PS3) on mobile devices. We're almost there. The move to Kepler with Logan is a big deal for NVIDIA. It finally modernizes NVIDIA's ultra mobile GPU, bringing graphics API partity to everything from smartphones to high-end desktop PCs. This is a huge step for game developers looking to target multiple platforms. It's also a big deal for mobile OS vendors and device makers looking to capitalize on gaming as a way of encouraging future smartphone and tablet upgrades. As smartphone and tablet upgrade cycles slow down, pushing high-end gaming to customers will become a more attractive option for device makers.

Logan is expected to ship in the first half of 2014. With early silicon back now, I think 10 - 12 months from now is a reasonable estimate. There is the unavoidable fact that we haven't even seen Tegra 4 devices on the market yet and NVIDIA is already talking about Logan. Everything I've heard points to Tegra 4 being on the schedule for a bunch of device wins, but delays on NVIDIA's part forced it to be designed out. Other than drumming up IP licensing business, I wonder if that's another reason why we're seeing a very public demo of Logan now - to show the health of early silicon. There's also a concern about process node. Logan will likely ship at 28nm next year, just before the transition to 20nm. If NVIDIA is late with Logan, we could have another Tegra 3 situation where NVIDIA is shipping on an older process technology.

Regardless of process tech however, Kepler's power story in ultra mobile seems great. I really didn't believe the GLBenchmark data when I first saw it. I showed it to Ryan Smith, our Senior GPU Editor, and even he didn't believe it. If NVIDIA is indeed able to get iPad 4 levels of graphics performance at less than 1W (and presumably much more performance in the 2.5 - 5W range) it looks like Kepler will do extremely well in mobile.

Whatever NVIDIA's reasons for showing off Logan now, the result is something that I'm very excited about. A mobile SoC with NVIDIA's latest GPU architecture is exactly what we've been waiting for. 

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  • kukarachee - Wednesday, July 24, 2013 - link

    Yes indeed. This looks to be another SOC that will tank just like Tegra 4 has totally crashed and burned (literally ;) ) with little success in the market. Tegra 4 was a flop, with power consumption and heat output so poor it needs a fan to keep it cool in some cases.

    Nvidia should stop burning money with the continued Tegra failures.

    This also ignores the 1000lb gorilla that is Intel wading into the SOC space, who no one, not even the big players like Qualcomm or Samsung, much less a small-fry like nvidia, will have much success competing against once they get rolling with their SOCs built using their exclusive and superior foundry technology.
  • Eric S - Wednesday, July 24, 2013 - link

    Not that Tegra and Apple processors really compete, but Apple is rumored to be teaming up with Intel for access to their fabs.
  • lmcd - Wednesday, July 24, 2013 - link

    Apple would be considered a competitor and probably won't be accepted, I believe, unless Intel is giving access to old fabs. Read the official information before you post.

    Intel will probably never make ARM SoCs since they left the business.
  • Krysto - Thursday, July 25, 2013 - link

    Next year 3 Ghz 20nm ARM chips are rumored to arrive. Intel can't compete with that with Atom. Plus Atom's GPU is still no match for the average ARM GPU, let alone for Kepler.
  • Refuge - Thursday, July 25, 2013 - link

    I think they still have another tick and tock before Intel starts rampaging about in SOC land. But you do bring forward a valid point good sir.
  • Krysto - Wednesday, July 24, 2013 - link

    I definitely agree Logan needs to be 20nm next year, and I'm not sure Nvidia will do that. I do know they intend to have Tegra 6 after it, at 16nm FinFET.
  • rocketscience315 - Wednesday, July 24, 2013 - link

    The feature list is disingenuous as CUDA is nV specific (lots of others have OpenCL) and DX11 has no relevance except perhaps MS Surface.
  • Spunjji - Wednesday, July 24, 2013 - link

    Disingenuous? A marketing slide? Nevar ;D

    Quite true, of course. Unless they're planning to foist CUDA upon the mobile world it's not much of a draw; especially not in what will be a rather weak implementation of their compute architecture.
  • DanNeely - Wednesday, July 24, 2013 - link

    What about WP8.x? I'd assume it's using DX instead of OGL for 3d.
  • rocketscience315 - Wednesday, July 24, 2013 - link

    You're probably right about DX running on WP8 but I presume they can run OGL also, and developers would use OGL as it would make some code cross-platform. I'd bet that DX is a rather tiny market relative to OGL on mobile.

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