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...

Cortex A15: GPU Power Consumption Final Words
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  • gryer7421 - Friday, January 04, 2013 - link

    aaaand then looses where it matters, the rest of the platform. one more process shrink and both will be on even terms in cpu power usage and then as a whole platform will start punching arm in the face. Reply
  • Wolfpup - Friday, January 04, 2013 - link

    Huh? Did you read the article? Atom built on 32nm is competitive with ARM built on 28nm. Not only that, but it's looking like Haswell will realistically be able to compete here too, and we've got the second gen Atom coming up this year too...but TODAY'S Atom at an older process is competitive with ARM...what you're claiming is exactly the opposite of what the article says. Reply
  • JumpingJack - Friday, January 04, 2013 - link

    I don't think we are looking at the same data, overall Atom appears to uses the same or less power than Krait and offers better performance in general. Reply
  • Homeles - Friday, January 04, 2013 - link

    "Anyone with half a brain" would read the article before making such an idiotic statement. Reply
  • Rezurecta - Saturday, January 05, 2013 - link

    wow. Way to belittle Anand's hard work...

    Great article! One of the many reasons I love this site. :)
    Reply
  • Death666Angel - Friday, January 04, 2013 - link

    The Star Wars theme to play in my head! Thanks for that! :D Reply
  • Death666Angel - Friday, January 04, 2013 - link

    "I wonder what an 8W Haswell would look like in a similar situation."
    Me too. However, considering that they 17W ULV parts only reach those numbers by throttling as well, I don't expect a lot.
    Reply
  • carancho - Friday, January 04, 2013 - link

    Amazing work. Congratulations! A couple of presentation suggestions:

    Next time please smooth some of the most important charts. The volatility makes it hard to see where the averages are. Take this chart: http://images.anandtech.com/reviews/SoC/Intel/CTvK... it could really benefit to have another copy with some additional smoothing.

    Also, in power charts like this http://images.anandtech.com/reviews/SoC/Intel/CTvK... it would be helpful to have as a summary followup chart the power calculation done and presented as bar charts; otherwise we have to resort to calculate the differences in the areas below the lines with our eyes, and they can be deceiving.
    Reply
  • carancho - Friday, January 04, 2013 - link

    I hadn't reached the A15 part yet when writing this. Ignore the 2nd comment. Reply
  • amorlock - Friday, January 04, 2013 - link

    I'm frankly amazed and impressed that Intel can get Haswell down to 8W but it's hard to imagine it in a mid range mobile device because of the likely unit cost. The reason Atom has stagnated until recently is because Intel doesn't want to create a chip that cuts into it's very profitable mainstream CPU market. Reply

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