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Nvidia talks up dual-core power saving

Nvidia talks up dual-core power saving

Nvidia's white paper makes the claim that a dual-core CPU can draw 40 percent less power for the same workload.

In the hopes of turning more manufacturers on to its Tegra line of mobile-oriented chipsets, Nvidia has released a whitepaper that claims multi-core computing to be the future for smartphones and tablets - and even makes the claim that multiple cores can save, rather than cost, you power.

The paper, entitled 'Benefits of Multi-core CPUs in Mobile Devices,' predicts that dual-core processors will become the norm for mobile devices in 2011, and that quad-core chips will arrive shortly after.

It's not all about pushing more processing power into a device, however: the company claims that 'mobile devices like smartphones and tablets benefit even more from multi-core architectures because the battery life benefits are so substantial.'

To demonstrate how such a seemingly contradictory stance - adding additional cores resulting in lower power usage - is possible, Nvidia takes the example of a pair of identical mobile devices: one runs a single-core ARM Cortex-A9 chip, while the other features a dual-core ARM Cortex-A9 chip. In both cases, the processors are identical in specification aside from the number of processing cores.

In the paper, Nvidia argues that under a complex workload - running Internet radio, web browsing, and playing Flash content - the single-core chip will run at 100 percent utilisation and have to run at the maximum frequency of 1GHz while drawing 1.1V. Nvidia rates the power draw of the chip as P.

For the same workload on the dual-core CPU, however, the tasks can be shared, leaving each core at 50 percent utilisation. Because the CPU isn't maxed out, it can be run at the slower speed of 550MHz to achieve the same workload - meaning a drop in voltage to 0.8V.

Overall, Nvidia claims, the dual-core processor has a power draw under the same workload of 0.6P - or a 40 percent saving over a single-core chip.

While the rest of the white paper - which you can download as a PDF from Nvidia - concentrates on selling the benefits of Nvidia's Tegra 2 platform specifically, the power saving claims should be of interest to all.

Are you convinced by Nvidia's calculation, or do you doubt that a simple switch to a dual-core architecture can yield such impressive power savings? Share your thoughts over in the forums.

14 Comments

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thehippoz 8th December 2010, 16:57 Quote
that's cool.. like professional juggling
mjm25 8th December 2010, 17:17 Quote
did they actually test it or did they just do the calculations? I learned a long time ago not to trust mathemeticians...
wuyanxu 8th December 2010, 17:19 Quote
Quote:
In the paper, Nvidia argues that

from my experience with journals, nVidia used ............. Maths.

(it's pretty hard to achieve Prof Farnsworth's effect in latest Futurama season using text)
Lazy_Amp 8th December 2010, 17:27 Quote
Didn't Tegra2 get dropped by Boxee when they were making their set-top box cause it couldn't run all 1080p formats?

In any case, to get this kind of performance, you'd need really stringent and complex power draw flows both on the hardware and in the OS. I am unsure that the power saving can actually be maximized as perfectly as it is laid out here.
schmidtbag 8th December 2010, 18:12 Quote
i've thought of this about a full year before nvidia came up with this idea, and it really works. but, theres 1 problem with it. since using 2 cores can reduce the amount of cpu utilization which therefore reduces the frequency, which allows a lowered voltage, if the 2 cores end up being maxed out, then they use up significantly more power and cause more heat (and heat makes electricity less efficient), which therefore makes the 2 cores less valuable. if people have a more powerful device, they're going to want to take advantage of it. also, if both devices are idled, the dual core will still use up more power since it (theoretically anyway) has more electronics inside, which adds up electric resistance.

as i see it, the key is multi-threading. that would help reduce the amount of cpu usage without adding more electronics. unfortunately, the pentium 4, i5, and i7 are currently the only CPUs capable of that and its taken about 10 years for amd to finally invest in it, so i doubt we'll be seeing any arm chips doing this any time soon.
javaman 8th December 2010, 19:31 Quote
Depends on how well programmed the software is. What if said dual core wanted to run everything on one core and let the other idle?
schmidtbag 8th December 2010, 19:57 Quote
Quote:
Originally Posted by javaman
Depends on how well programmed the software is. What if said dual core wanted to run everything on one core and let the other idle?

thats an excellent point but, depending on how the OS handles the process, it could be divided between both cores, making them used at 50%. this doesn't stress them enough to make them use too much more power.
javaman 8th December 2010, 20:38 Quote
Quote:
Originally Posted by schmidtbag
thats an excellent point but, depending on how the OS handles the process, it could be divided between both cores, making them used at 50%. this doesn't stress them enough to make them use too much more power.

Personally I think the advantage would come from having more processing power per area like combining CPU with GPU, more cores is easier than IPC or increasing frequency. It really just reopens the faster single core vs slow dual core debate. The point that would make more sense sale wise is

completion time X Power per min = power useage

They've went about proving "dual > single" core in a weird way.
Lazy_Amp 8th December 2010, 20:41 Quote
Quote:
Originally Posted by schmidtbag
also, if both devices are idled, the dual core will still use up more power since it (theoretically anyway) has more electronics inside, which adds up electric resistance.

In that case, you;d have to have a way to actually shut off voltage to the second core. As long as you have each core on different supplies, theoretically some control system could be developed to shut down a core if, say, the phone is in a lock/idle state.
Krayzie_B.o.n.e. 8th December 2010, 21:32 Quote
yeh dual core CPU in mobile devices then next year 4 core cpu in mobile devices and then
in 2013 we will get mobile devices with pci-e slots, water blocks, neon lights, and plexiglass cases.
meanwhile the iPhone 5gs WiMax version 2.0 will be as thin as a credit card with a magnetic strip on it and you will literally just swipe it to give Apple free money.

muha hah ahh ha haaa.
Skiddywinks 8th December 2010, 22:54 Quote
Quote:
Originally Posted by schmidtbag
...also, if both devices are idled, the dual core will still use up more power since it (theoretically anyway) has more electronics inside, which adds up electric resistance.

I don't know precise numbers, but since all current ARM architectures are fully power gated (or at least mostly, if I am simply crossing a new SoC with the current SoCs), two cores doing nothing is still going to draw zero power.

As for both cores going full whack, well, that is a possibility. However, as mentioned, it all depends on the software. If checks are not in place to make sure software doesn't use more resources than it needs, then you could very quickly be running for the power outlet.

An argument I see a lot on the internet is that while a lot of the more powerful CPUs (or CPUs with more cores) may draw a lot more power, they finish whatever task they are doing a lot quicker. It often works out more efficient to use two cores and finish the task in less than half the time. When comparing using things like loading, compressing, and other finite tasks, this makes perfect sense to me; two cores drawing nothing still equals nothing, and if the two cores are finishing tasks more than twice as fast, well, we have a winner.

Thing is, apart from the loading and responsiveness of phones, which obviously would benefit from this kind of upgrade, people very rarely spend much time waiting for such tasks, and instead will be playing games or watching a movie on their phone. These tasks, unless controlled to only use what they need, would utterly destroy any good that the upgrade to dual cores achieves, at least in terms of battery life.

To be fair, I do think multicore CPUs in phones is a great idea, but as we often see in the tech industry (especially recently), the hardware can be the dog's bollocks, but if the software doesn't make use of it correctly, well, it's pretty useless.

At the end of the day though, the screen is by far the most power hungry component of any phone (and let's not forget the cell radio), so all of this talk is pretty moot when you start looking at the phone as a whole.
schmidtbag 8th December 2010, 23:23 Quote
Quote:
Originally Posted by Skiddywinks
Quote:
Originally Posted by schmidtbag
...also, if both devices are idled, the dual core will still use up more power since it (theoretically anyway) has more electronics inside, which adds up electric resistance.

I don't know precise numbers, but since all current ARM architectures are fully power gated (or at least mostly, if I am simply crossing a new SoC with the current SoCs), two cores doing nothing is still going to draw zero power.

As for both cores going full whack, well, that is a possibility. However, as mentioned, it all depends on the software. If checks are not in place to make sure software doesn't use more resources than it needs, then you could very quickly be running for the power outlet.

An argument I see a lot on the internet is that while a lot of the more powerful CPUs (or CPUs with more cores) may draw a lot more power, they finish whatever task they are doing a lot quicker. It often works out more efficient to use two cores and finish the task in less than half the time. When comparing using things like loading, compressing, and other finite tasks, this makes perfect sense to me; two cores drawing nothing still equals nothing, and if the two cores are finishing tasks more than twice as fast, well, we have a winner.

Thing is, apart from the loading and responsiveness of phones, which obviously would benefit from this kind of upgrade, people very rarely spend much time waiting for such tasks, and instead will be playing games or watching a movie on their phone. These tasks, unless controlled to only use what they need, would utterly destroy any good that the upgrade to dual cores achieves, at least in terms of battery life.

To be fair, I do think multicore CPUs in phones is a great idea, but as we often see in the tech industry (especially recently), the hardware can be the dog's bollocks, but if the software doesn't make use of it correctly, well, it's pretty useless.

At the end of the day though, the screen is by far the most power hungry component of any phone (and let's not forget the cell radio), so all of this talk is pretty moot when you start looking at the phone as a whole.

Hmm, i wasn't aware of the power grating, so i guess that nulls that argument haha.
i completely agree on what you said about more cores completing tasks quicker, but keep in mind that usually if you're doing a strenuous task on a mobile device; it isn't going to be something with a fixed goal, such as encoding a video. typically strenuous tasks on mobile devices will be games, where they might want to be played for longer than the battery life supports.

i too think its a good idea for multicore CPUs to be in phones, but it really comes down to how you use your phone. if you want good battery life and don't do anything complicated, a dual core is great. if you do strenuous tasks and you care about battery life, get a single core (most apps are designed for single cores anyway so its not like you're really missing out). if you multitask and you don't care about battery life, get the dual core.

if companies really want to get better battery life with screens they need to invest in OLED screens
javaman 9th December 2010, 00:59 Quote
Quote:
Originally Posted by schmidtbag
Hmm, i wasn't aware of the power grating, so i guess that nulls that argument haha.
i completely agree on what you said about more cores completing tasks quicker, but keep in mind that usually if you're doing a strenuous task on a mobile device; it isn't going to be something with a fixed goal, such as encoding a video. typically strenuous tasks on mobile devices will be games, where they might want to be played for longer than the battery life supports.

i too think its a good idea for multicore CPUs to be in phones, but it really comes down to how you use your phone. if you want good battery life and don't do anything complicated, a dual core is great. if you do strenuous tasks and you care about battery life, get a single core (most apps are designed for single cores anyway so its not like you're really missing out). if you multitask and you don't care about battery life, get the dual core.

if companies really want to get better battery life with screens they need to invest in OLED screens

TBH the nature of the way phones are used, ie constantly doing something simple, I can't see battery life improving short term. while a 1GHz chip is more than plenty for a phone, people are starting to demand more from their device weather it be faster games, prettier graphics, 1080p etc. Look at the tablet market and upcoming PSP phone. they will most benefit from faster processors but like intel and AMD discovered, you can't go down the route of raw MHz forever otherwise power useage and heat will get out of control. ARM and VIA are both committed to highly efficient processors so regardless if they stay single or dual core but like I said above, theres only so far you can go with IPC and MHz. Dual cores will happen and this is what Nvidia are really pushing for possibly earlier than other companies, since their main market is GPU which uses highly parallel design to achieve its performance. All companies can benefit from lessons learnt in the ULV market.

Everything is becoming more efficient but the smart phone and ultra portable market are still trying to get enough speed while using the same size battery. 1GHz is just about enough for what a smart phone does, but again games and people who want 1080p output will always ask more. I totally agree tho, the biggest power savings will come from new screen technology. Sinking crazy billions to gear FABs for the next process is soon coming to its EOL.
kzinti1 9th December 2010, 21:01 Quote
Very interesting article. From the people that make the most power-hungry video-cards in all existence!
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