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Does Saving Power Mean Hurting Performance?

Does Saving Power Mean Hurting Performance?
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It seems like everyone in the tech industry recently jumped on the same bandwagon. Whether they call it green computing or the quest for efficiency, the end goal is the same: to decrease power requirements in all PC-component categories and to focus on performance per watt rather than all-out horsepower. Obviously, value takes on a new meaning in such a context, but performance remains a key focus. So, we wanted to dive deeper into the performance impact of power-saving technologies on today’s processors and motherboards.

The Power Consumption Issue

The discussion about power consumption and power efficiency isn’t new, but it has become a central issue among hardware manufacturers, due in part to increasing energy costs. The point of contention is that because PC components utilize different amounts of power when they’re active or idle, we believe that a component should only utilize as much power as required to do its work.

History Of Coverage With A Focus On Power And Efficiency

Tom’s Hardware was one of the first publications to criticize excessive power consumption across multiple hardware components and to talk about more efficient computing options. The focus has historically centered on processors, since they're often the most power-hungry devices inside a PC. This has changed a lot in recent years, as upper-mainstream and high-end graphics cards tend to be the power hogs today.

Coverage milestones :

Power Savings Work. What’s Next ?

With more manufacturers becoming aware of the new market requirements, components increasingly consume less power while delivering more performance than their predecessors. One of the best examples has been Intel’s Core 2 Duo, which consumes half the power as a Pentium D dual core (don’t confuse it with the Pentium Dual Core, which is based on the Core 2 family) while delivering much more performance. Other examples can be found in the storage segment, where WD’s latest Green drive outperforms many conventional drives.

While there are limits to power savings, which are defined by the technology used, we expect efficiency to keep increasing. This means that the power consumption of mainstream components should continue to decrease or stay at today’s levels, while performance will continue to improve. Combining lower power and more performance also significantly boosts efficiency. Let’s look at the two ways processor power consumption can be improved before comparing some benchmark results of systems with various popular power-saving settings versus system running at full tilt.

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  • -6 Hide
    SanDiego , December 17, 2008 10:34 AM
    Correction: Graphics card in set-up should be a 4850, never heard of a 485 it must be pretty fancy
  • 1 Hide
    malveaux , December 17, 2008 12:22 PM
    Interesting.

    So there's basically no real difference. Might as well save some power.

    Thanks!
  • 2 Hide
    KyleSTL , December 17, 2008 1:59 PM
    The difference was very small (2%) in performance, but the power consumption difference could have been much smaller.

    The PSU that was used was WAY oversized and was only loaded 10-21% of capacity during the entire test. PSU efficiency in that range is terrible. A 430-500W PSU (like the Earthwatts series) would have been reasonably loaded and the efficiency would not have been so drastically different across the range of loads.

    Efficiency example


    The difference in efficiency between 10 and 20% is massive, compared to 30-40%.
  • 1 Hide
    chaohsiangchen , December 17, 2008 2:36 PM
    You guys should do the same test on Phenom and Athlon (K8). Phenom's cores can run at different speed. CnQ also put CPU cores at lower frequency (1GHz or 1.25GHz) compare to Intel SpeedStep. Performance impact from energy saving on Phenoms is much obvious.
  • 3 Hide
    JimmiG , December 17, 2008 2:44 PM
    I agree, you need to do a follow up with the Phenom. I have experienced erratic performance with my X4 9650 @ 9950 in some cases. For example if a GPU limited games puts the CPU load of a core just at the threshold value for the power saving to kick in, that core will keep going in and out of power saving mode, causing stutters and lower overall framerates (>10% difference). I've experienced this in 3DMark 06, UT3 rolling demos and the X3 space sim among other games. The same thing might probably happen during other tasks such as file compression. Turning off power saving solved all such problems. I've now made it a habbit to always turn off power saving before launching games or compressing large archives.
  • 1 Hide
    nebun , December 17, 2008 3:46 PM
    Chaohsiangchen

    i totally agree. this is why AMD is still in the CPU market, they make a much more efficient cpu when it come to energy efficiency, and the price is not that bad at all.
  • 1 Hide
    KyleSTL , December 17, 2008 4:02 PM
    Quote:
    this is why AMD is still in the CPU market, they make a much more efficient cpu when it come to energy efficiency

    BS
    Stop perpetuating a lie. Intel took over the lead long ago. Athlon is much better than any Netburst, but Core 2 is much greater than anything AMD had ever put out.
  • 3 Hide
    chaohsiangchen , December 17, 2008 4:08 PM
    NeBuNi totally agree. this is why AMD is still in the CPU market, they make a much more efficient cpu when it come to energy efficiency, and the price is not that bad at all.


    Only partly right. Those low power Brisbane Athlons are good, but Phenoms are still power hogs even under CnQ with highest possible energy saving option.
  • 2 Hide
    zodiacfml , December 17, 2008 5:26 PM
    yep, core2duo's are better in efficiency than athlons since it finishes tasks in less time.
    anyways, we started noticing power efficiency when that article came out of overclocking a pentium M that performs far better than a pentium 4 using less power and that was really amazing. that was the grandfather of the core2. hehe
  • 0 Hide
    nerrawg , December 17, 2008 6:21 PM
    KyleSTL

    I don't really understand your point because they were not looking at the power efficiency of the PSU or how different PSUs can effect CPU efficiency. They were trying to solely look at CPU efficiency and how power saving on CPU's affect performance. To do this I think they chose an oversized PSU so that the PSU was excluded as a variable, or in lay-mans terms: it had as little possible affect on the CPU comparison. This is because the cpus could draw as much power as they wanted to.

    I don't think that the wattage of a PSU will change the efficiency of a CPU, it changes the efficiency of the PSU! It can effect the performance of a CPU by limiting its power supply, but it does not change its efficiency - it only restricts the CPUs potential.

    PSUs are however very important in system efficiency as they are the main link between the external power supply and the system. Having a good PSU that is balanced to your system power needs will give you better overall efficiency as you stated.
  • 0 Hide
    nerrawg , December 17, 2008 6:27 PM
    A very interesting and informative article, thanks TOMs! I thought the power saving modes were simply gimmicks that made unattractive sacrifices in performance, seems I was wrong in this case.
  • 0 Hide
    KyleSTL , December 17, 2008 9:04 PM
    Quote:
    I don't really understand your point because they were not looking at the power efficiency of the PSU or how different PSUs can effect CPU efficiency. They were trying to solely look at CPU efficiency and how power saving on CPU's affect performance. To do this I think they chose an oversized PSU so that the PSU was excluded as a variable, or in lay-mans terms: it had as little possible affect on the CPU comparison. This is because the cpus could draw as much power as they wanted to.

    I don't think that the wattage of a PSU will change the efficiency of a CPU, it changes the efficiency of the PSU! It can effect the performance of a CPU by limiting its power supply, but it does not change its efficiency - it only restricts the CPUs potential.

    PSUs are however very important in system efficiency as they are the main link between the external power supply and the system. Having a good PSU that is balanced to your system power needs will give you better overall efficiency as you stated.

    Because they measured the power consumption at the wall (i.e. AC) not the DC the system actually uses, that's why.

    Ideally they should have used a PSU sized so that the efficiency doesn't differ more than 2% during the entire scope of testing, to eliminate it's influence. They had a PSU sized that the efficiency differed ~8-10% during the measured values.
  • 0 Hide
    nerrawg , December 17, 2008 11:41 PM
    Ah, well in that case you are right.
  • 0 Hide
    yyrkoon , December 19, 2008 6:13 PM
    What someone needs to do other than testing power efficiency is test how low in power AMD, and Intel can go. I have seen data on an Intel E2140 CPU based system that uses ~50W, and I have an older AM2 1210 opteron system (CPU TDP of 103W ) that uses less than 80W including a 19" WS LCD. My gaming rig on the other hand which is an Intel P35/ICH9R board, and an E6550 CPU, with an nVidia 9600GT *can* use up to ~220W while playing World in Conflict ( which I have found to be the most CPU/GPU intensive game that I currently own). Idle on this system is ~168W, which is where this system peaks with a 7600GT for discrete graphics.

    Anyhow, my point here is that while efficiency may be important in a data center, lower system power can be more important at home. Maybe a lower powered system will take longer to do CPU intensive tasks, but at home a computer is going to be idle a lot. If you're a gamer perhaps not, but a person running off solar/batteries, definitely. Web browsing, and similar tasks barely use any CPU %. Even with this opteron I have, underclocked to 500Mhz, at .8v does this perfectly fine. Sure, and Atom based system could do this fine to, but does not have the potential to be bymped back up to normal when and if the need arises.

    Anyhow, I am thinking with an AMD 740G based board, and an AM2 4850e, there is no Intel based system that can match it in performance, and power consumption. Even *if* an E2140 could match a 4850e in performance, I doubt the total system power consumptions could be matched. Also, let us not forget about the AM2 on CPU memory controller, which can improve performance greatly even while underclocked. Either way, I would like to see some data proving, or disproving my theory here.