The x86 Power Myth Busted: In-Depth Clover Trail Power Analysisby Anand Lal Shimpi on December 24, 2012 5:00 PM EST
In all of these tests you're going to see three charts. The first will show you total platform power, measured at the battery, taking into account everything from SoC to display. The next shows you power measured at the CPU power delivery circuit, and the third shows you power measured at the GPU power delivery circuit. All values are measured in watts, and are reported in 15ms intervals (although I sampled at 1KHz then averaged down to 15ms).
For our first set of tests I simply wanted to get a feel for idle power. Both systems had all background syncing suspended, WiFi was connected, and we're just sitting at the Windows RT/8 Start Screen until the tablets reached a truly idle state. Note that idle under Windows RT/8 technically doesn't happen until the live tiles stop updating, which you'll see denoted by a drop in the idle power consumption in the graphs below.
First up is total platform power consumption:
Surface RT has higher idle power, around 28% on average, compared to Acer's W510. The last half of the graph shows the tablets hitting true idle when the live tiles stop animating.
A look at the CPU chart gives us some more granularity, with Tegra 3 ramping up to higher peak power consumption during all of the periods of activity. Here the Atom Z2760 cores average 36.4mW at idle compared to 70.2mW for Tegra 3.
The GPU specific data is pretty interesting - the GPU power rail shows much high power consumption than on Intel's Z2760. As I didn't design Tegra 3, I don't know what else is powered by this rail - although you'd assume that anything else not in use would be power gated. Imagination Technologies' PowerVR SGX 545 does appear to be quite power efficient here, on average using 155mW while rendering the Start Screen.
I wasn't happy with the peaks we were seeing when nothing was happening on the systems, so to confirm that nothing funny was going on I threw both tablets into airplane mode and waited for full idle. Check out the tail end of the platform power diagram:
That's much better. Without the AP talking to each tablet's WiFi radio constantly, idle becomes truly idle. If you're curious, the power savings are around 47.8mW (average) for the W510 in airplane mode when fully idle.
The GPU rail feeding the Atom Z2760 appears to hit a lower idle power when compared to NVIDIA's Tegra 3. Advantages in idle power consumption are key to delivering good battery life overall.
Post Your CommentPlease log in or sign up to comment.
View All Comments
runner50783 - Monday, December 24, 2012 - linkThis is why I don't care if you post your podcast on time : P, you guys are the best when it comes to technical analysis and reviews, you are the reference for the rest of the review sites, keep it up!
Well, I guess graphics power may be the only advantage of tegra 3 over clover trail right now, and that may change with proper drivers too... Now it really makes little sense to have an RT based system, I feel bad for pulling the trigger on a Surface RT after playing with a Clover trail tablet, it was much faster on almost everything except games.
designerfx - Tuesday, December 25, 2012 - linkThis is the first time in a long while that I've seen Anandtech declare that something which isn't accurately measured, is actually accurately measured and compared.
I'm quite disappointed, honestly. 5th core on the Tegra is a significant part of what defines its power savings, and yet they're saying "Welp. It's about the same!".
I'm really questioning this a lot, Anand.
Deo Domuique - Thursday, December 27, 2012 - linkThis is his yearly fat bonus by Intel :P
As for us, just ignore it and move on.
MrSpadge - Saturday, December 29, 2012 - linkWhat the ...?! If there's currently no way to enable the 5th core in Win 8, what exactly are they supposed to do? I'm sure Anand would love to repeat these tests if any way to fix this was available.. but right now that's how both devices perform. Call Tegra 3 crippled on Win 8 if you want, as that's what it apears to be.
Activate: AMD - Saturday, December 29, 2012 - linkWhats the problem? They're comparing performance under the windows RT environment and Anand mentions on the very first page:
"One last note: unlike under Android, NVIDIA doesn't use its 5th/companion core under Windows RT. Microsoft still doesn't support heterogeneous computing environments, so NVIDIA had to disable its companion core under Windows RT."
The only thing thats disappointing here is your inability to comprehend whats being tested.
Wolfpup - Thursday, January 3, 2013 - linkThat would improve idle performance, but this is a real world test for the time being, and even still-Atom is more powerful, and yet uses less power, AND of course because it's more powerful, finishes doing work faster.
Even if that fifth core were supported, this is still quite nifty.
The fact that I can, today, buy an actual x86 PC that can easily double as an iPad class ebook reader/light web browsing tablet is just amazing. (eInk's better, but you know what I mean).
Alexvrb - Thursday, December 27, 2012 - linkI'm not a huge fan of Tegra 3, but I wouldn't regret your Surface purchase too much. My dad has one, it's built better than any other tablet I've held. Plus Inte's solution is almost entirely unsatisfactory for 3D gaming. Intel is only using a single SGX 545 core. They clock it pretty high, but it isn't enough. The latest iPad uses a 4-core SGX 554 solution, and clocked right it seems to do pretty darn good on power too. Clocks aren't as high but it blows both the Tegra 3 and any ULV Atom out of the water.
I'm not a huge fan of Apple either, but they generally use the most cutting-edge Imagination Technologies IP available. That might include Rogue (Series 6) in the next go around... Intel needs to get Series 6 in their chips ASAP.
Oh, and graphics drivers? Intel? Good luck! If this was Nvidia or AMD I might have agreed with you.
ssj3gohan - Monday, December 24, 2012 - linkThis is really pornographic power electronics stuff. I do this stuff every day with my ultra-power efficient computer projects, but I didn't know that Intel walked around with this kind of a setup to show transparently what they are doing with power consumption.
Good work, Intel. Now go and apply your knowledge to desktop platforms as well, because I'm kicking your ass here. I have yet to come across a desktop platform that cannot be made at least 50% more power efficient just through power electronics hacks.
madmilk - Monday, December 24, 2012 - linkDid anyone honestly think Intel, with a hundred times the revenue of ARM, would let themselves be devoured?
Intel will still trouble entering the mobile device market because of the ISA lock-in ARM enjoys. On the other hand, ARM at this moment does not stand a chance in the (micro)server market either, especially as Intel increases its server Atom line.
tipoo - Monday, December 24, 2012 - linkYeah, I think Intel will do fine and remain the 900lb gorilla in the mobile arena as well. ARM has the lead now, but once Intel has its sights set on something vital to its interests it tends to destroy the competition.