Can Quads actually use less energy than dual cores?

[nyker96]

I was thinking about the energy usage but came up to this interesting interpretation. I mean let's say we use a computer to compress a video file. This compression takes 2 hrs on a quad and about 3.5hrs on a dual core. Unless the total energy expenditure of a dual core running at max can be better than 60% of quad core system which is unlikely, then the quad core will end up saving you energy over time. If a quad runs about 300W at peak load for 2 hrs that's total 600 W.hr of energy. That means for the dual core to beat it in terms of energy saving it must run no more than 171W which we know isn't possible since CPU is only a part of total energy consumption not all. I would believe that if a fully OCed quad runs at 300W peak, a comparable fully OCed dual core will probably have to do 230W since other things in the system are identical. This means people running quads not necessarily is using more energy on the long run, in fact, they use less because they don't need to keep the rest system running as long as dual core users thus saving energy.

What you guys think?

 

[TuxDave]

I didn't work out the math but I agree for the most part. It kinda depends on the application that the quad-core is working on. For most jobs which have a clearly defined workload, then I believe that we should take performance into account when trying to judge how power efficient something is. If a processor can finish something in half the time then that means it won't be running under a full load for as long as another processor.

On the other hand, for things that don't have a clearly defined workload such as rendering games. The extra performance just translates into higher FPS (just creates more work) and the overall time that the CPU must crunch remains relatively constant. In that work model then we can't take advantage the performance based power savings.

 

[Phynaz]

Techreport includes these calculations in their reviews.

The answer is, yes, it's possible.

 

[Cogman]

I don't quite agree with the conclusions arrived at here. Yes when you overclock you do try more components then the CPU. But in general the CPU is the main component stressed. 4 cores are not twice as fast as 2 cores are, but they do take up twice as much power as 2 cores, especially in intels design where the processors are basically just 2 dual core processors on one chip.

I don't know what video encoder you use, but the ones I have used don't seem to gain huge benifits from multiple threads (by huge I mean that 2 threads aren't twice as fast as one) instead I see somewhere around a 30% increase for 1-2. I have heard as well (don't own a quad) that that increase is even smaller with more threads. The next thing you did not account for is the fact the Quad cores eat more energy at Idle. So even if you are correct about them using less energy to encode that would mean you always turn your computer off right after you do anything intensive that will be completed after X amounts of cycles are completed (Gaming will NOT save energy with a quad core).

Interesting thought but just not true in the real world.

 

[Cogman]

BTW this is just based on current processors available. AMD's Phenom is supposed to support independent ramping of individual processors. That could result in some savings as one processor could have a full load while the other 3 will be idling at a low wattage. That could put it in the position where it will have greater power savings then a Intel Conroe (or any processor that does not use individual core speed rampings.) However, Overclockers will probably turn this feature off first on AMD's new cores

 

[nyker96]

Originally posted by: Cogman
I don't quite agree with the conclusions arrived at here. Yes when you overclock you do try more components then the CPU. But in general the CPU is the main component stressed. 4 cores are not twice as fast as 2 cores are, but they do take up twice as much power as 2 cores, especially in intels design where the processors are basically just 2 dual core processors on one chip.

I don't know what video encoder you use, but the ones I have used don't seem to gain huge benifits from multiple threads (by huge I mean that 2 threads aren't twice as fast as one) instead I see somewhere around a 30% increase for 1-2. I have heard as well (don't own a quad) that that increase is even smaller with more threads. The next thing you did not account for is the fact the Quad cores eat more energy at Idle. So even if you are correct about them using less energy to encode that would mean you always turn your computer off right after you do anything intensive that will be completed after X amounts of cycles are completed (Gaming will NOT save energy with a quad core).

Interesting thought but just not true in the real world.

I don't think a dual core system that uses 250W working at full load will double to 500W when you swap it with a quad core CPU and keep the rest of the system in tact. As to performance increase, I do agree quad don't mean 100% increase, that all depend on the software threading model but as time goes, more and more software will be optimized to quad core. look at this article:
http://www.anandtech.com/cpuch...owdoc.aspx?i=2866&p=14

I see some software has no advantage on quad but others got a 50% boost. So I think if the use of quad matches the right software for it, he/she will actually end up saving money on the long run, either that or do more work within the same amount of energy.

 

[Cogman]

Originally posted by: nyker96

I don't think a dual core system that uses 250W working at full load will double to 500W when you swap it with a quad core CPU and keep the rest of the system in tact. As to performance increase, I do agree quad don't mean 100% increase, that all depend on the software threading model but as time goes, more and more software will be optimized to quad core. look at this article:
http://www.anandtech.com/cpuch...owdoc.aspx?i=2866&p=14

I see some software has no advantage on quad but others got a 50% boost. So I think if the use of quad matches the right software for it, he/she will actually end up saving money on the long run, either that or do more work within the same amount of energy.

The system itself will not double, but when you consider that a stock Conroe is a 65 watt device and a quadcore is 100 watt device you can quickly see that it is something like an 80% increase in power consumption of the cpu. Now if you have all components exactly the same then their power consumption is ruled out and you begin to JUST look at the cpu power consumption. I have never heard or seen a program that gains a full 50% Performance increase from using a quad core. So even if it does exist, they are few a far between. The only way you could truely get a full 50% speed increase is by running X number of processes for the amount of cores you have. It is just a truth that no matter how good your threading model is you will never get a full use of the core because you have to allocate your thread handler to one core or the other.

Now, you didn't address the fact that a quad core system will use more power then a dual core system at ideal. Again, most computer arn't run at full blast so the down time will eventually catch up to you and that alone will make you use more electricity then just a dual core processor.

I see what you are saying though, but most components aren't be power drawers. The only place you might save a lot of energy is if you have 2 8800GTX Video cards in your computer. Most components just don't take a lot of power, the CPU is one of the biggest offenders when you look at the power draw of your system (video cards are next)

 

[nyker96]

I do see from the benchmarks off the link, the encoding jobs, quads gains about 50% on WME9 for instance. However, I do agree with your point that at idling quads will eat up more, thus, I believe it's depend on the usage pattern of the user. If the user uses apps that optimized for quads and is using it quite heavily then I think quad might xome out on top, however, I have to admit for us average user who keeps the machine mostly idling quads will cost relatively more on the long run.

 

[firewolfsm]

Well ya, adding cores improves performance per watt, that's kinda the point.

 

[coldpower27]

http://xbitlabs.com/articles/c...me-qx6850_6.html#sect0

It really depends some jobs gain tremendous performance from Dual-Quad.

 

[Makaveli]

how about comparing a 6600 quadcore to a Pentium D 940 which ones uses more power?

 

[VirtualLarry]

I agree that moving to quad-core can help your performance-per-watt significantly.