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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  • Krysto - Wednesday, July 24, 2013 - link

    And you think Kepler isn't? Kepler is scalable as far as Nvidia's highest end chips. Plus that argument is a pretty weak one, since what matters is how much can you scale under a certain power envelope - not how much in TOTAL. That's completely irrelevant. It just means Series 6 will - eventually (years from now) get to 1 TF. But so will other chips.

    Also Kepler IS something special. Here's why - full OpenGL 4.4 support. Imagination, Qualcomm and ARM have barely gotten around to implement OpenGL ES 3.0, and even that took them until now basically, to implement the proper drivers for them, and obtain the certification.

    The point is, that the same performance level, Kepler optimized games should look a lot better than games on any other chip.
  • Krysto - Wednesday, July 24, 2013 - link

    Oh, and even Intel barely got around to implement OpenGL 4.0 in Haswell - the PC chip. So don't expect the others to support the full and latest OpenGL 4.4 anytime soon.
  • 1Angelreloaded - Wednesday, July 24, 2013 - link

    Incase you don't know this already, sandy/ivy/haswell integrated graphics are absolutely terrible, in most case when used aside your dedicated GPU it lowers performance instead of increasing it. On its own it might be fine for a few things here and there, but even that is terrible.
  • ExarKun333 - Wednesday, July 24, 2013 - link

    Your GPU knowledge is laughable. Integrated GPUs are disabled when running a dedicated. You obviously are a troll or are plain ignroant about all CPU/GPU issues. others please ignore this user's posts...
  • Flunk - Wednesday, July 24, 2013 - link

    Actually, you're wrong. In Nvidia Optimus/AMD Enduro the discrete GPU draws in the integrated graphic's frame buffer even when in discrete mode. Also, on desktops it is possible to enable your integrated graphics and discrete GPU at the same time to support more monitors.
  • lmcd - Wednesday, July 24, 2013 - link

    Difference is only present on Enduro. Optimus is almost identical. The performance hit with multiple monitors on multiple devices is likely a Windows thing and a framebuffer sync thing. Not an actual problem with Intel graphics.

    So I know we know Exar is wrong, but his point that Ang's information is irrelevant is in fact correct, for this mobile situation anyway.
  • happycamperjack - Wednesday, July 24, 2013 - link

    If you take a look at Microsoft's Surface Pro's benchmark number, you'd be shocked by how many times faster its GPU is compared to latest iPad and Androids phones. Because I was!
  • texasti89 - Thursday, July 25, 2013 - link

    "many times faster" is not the right metric .. they all about the same when you look at the perf/watt.
  • happycamperjack - Friday, July 26, 2013 - link

    I'm just dismissing the guy who's saying that integrated graphics from intel is absolutely terrible. It's certainly not terrible compared to the GPU in top mobile SoC.
  • Refuge - Thursday, July 25, 2013 - link

    Good sir, android (90% of what this will be running I would assume) JUST NOW with 4.3 which is yet to appear on a device (Nexus 7 R2 is first) just now implemented OpenGL ES 3.0 support.

    Look, being the first to support new API's is great, but being the only one gains you nothing because nobody is going to program for the 1% that's just bad business.

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