Tuning Cool'n'Quiet: Maximize Power And Performance, Part 2

Benchmark Results: SuperPi 1M And 8M

SuperPi is quite popular throughout the benchmarking world. As you can see, this benchmark is not really capable of fully utilizing two cores, let alone more than two. Like 3DMark 2001, a single- or dual-core processor is the better solution for this benchmark.

Or is it?

Do you remember the differences between these three processors? If you guessed synchronous clock changes, you're right. Since it can only fully utilize a single core, 3DMark 2001 and SuperPI repeatedly “jump” cores in Windows Vista, wasting time, and performance suffers as a result. Just look at the processor utilization graph again--it's as clear as day. Notice how the peaks and valleys on both lines mirror each other throughout the benchmark.

Let's see which processor completed the benchmark with the least amount of power.

Like 3DMark 2001, a performance penalty is incurred when we enable power management. But it’s a result of Windows Vista bouncing each single-threaded workload between physical cores, which idle independently from each other. Notice how the differences are smaller with the Phenom II compared to the Athlon X2 and Athlon II X2? Once we enabled synchronous clock changes in K10Stat (with the Optimized setting), we regained some of that lost performance back, though not all.

By enabling synchronous clock changes and shorter p-state transition times, we were able to regain performance, from losing 8-18% to just 2%. The benefit of shorter p-state transitions is about 1%, easily seen on the Phenom II results. In contrast, the penalty from asynchronous clock changes is about 17%, which is quite significant.

As a side note, we were able to compare single-threaded performance on the Phenom II, Athlon II, and the older Athlon X2. Working 400 MHz faster, the Athlon II offers the same single-threaded performance as the Phenom II X3 710. So, that 6MB L3 cache can make up for a 400 MHz clock deficiency. The presence of L3 cache also helped the older Athlon X2 from falling too far behind the newer Athlon II X2 250.

Let’s look at the power savings. With Optimized settings, not only did we regain some lost performance, we also saved around 16% of our power budget with the Athlon X2 7750. That's quite a difference compared to the default settings (4%). Now, if you’re looking for a good reason to buy the Athlon II X2 250, just look at the power consumption numbers. It’s about 8 watts lower than the Athlon X2 7750 and slightly faster.

Of course, the final measure is total power consumed by these processors during the benchmark. If you’re using stock Cool'n'Quiet settings (or no power management), there’s really not that much of a difference between the 45nm-based processors. But tweak the voltages and the Phenom II X4 945 steps ahead of the rest of the pack. You actually consume less power with this processor. This is pretty interesting, since this gives us an idea of what power consumption levels look like in single-threaded applications using these processors.

This thread is closed for comments
    Your comment
  • nzprogamer
    GO AMD go
    i am telling you my next build AMD/ATI
    """I WILL BE BACK"""
  • jedimasterben
    I'd be interested to see the tests performed on Windows 7 to see what the effect of reducing thread "jumping" would be.
  • cnox
    Dammit...how can this part 2 article be posted before the Building the Balanced PC Part 2?

  • melangex3
    Great Stuff. Keep up the good work. This is the type of review that will keep me coming back. How about throwing in the ever popular 720 BE and the new 620 or 630 just for giggles?
  • Ryun
    jedimasterbenI'd be interested to see the tests performed on Windows 7 to see what the effect of reducing thread "jumping" would be.

    I was thinking the same thing as well.

    Also, were the BIOSs all updated? The asynchronous clocks problem you're experiencing with Athlon II X2 was supposed to be fixed with updated CPU microcode.
  • Summer Leigh Castle
    620 and 720? :D
  • redgarl
    I must admit that lately AMD is impressive. I got a PII X3 720 BE unleashed at PII X4 20 fully stable with an Asus M4A78T-E latest BIOS. Let simply add that my 2 radeon 4850 OC in Crossfire are running as fast as 2 stock 4870...

    If you take into account that the 2 cards only cost 82$ each for a total of 165$ for the two... I can hardly believe that so little money can give so much results.
  • JimmiG
    With my Phenom X4 9650, I found Cool n Quiet to be pretty much worthless without tweaks. There were huge performance drops across the board, especially with tasks that didn't use all four cores, or only loaded cores partially. Videos and games would stutter and skip every couple of frames, compressing files would take longer etc. I basically had a 1.1 GHz CPU that would sometimes run at 2.3 GHz, if it felt like it. Too bad there was no tweak guide available then. I just disabled CnQ which solved all problems but made the system use more power and run hotter.

    With my 955BE, I haven't really had a need to tweak CnQ. It might cause a slight performance hit in some rare cases, but generally when I need a 3.2 GHz CPU, that's what it delivers.
  • tacoslave
    Nice, amd owns in the graphics department now with that $1.2 billion im sure amd is heading to pwn BOTH markets.
  • saint19
    Good!!!, I have my 955 to 3.8GHz at 1.5V....
  • marraco
    For this test, we've selected a 616MB folder full of files (the installer for Adobe Photoshop CS4)

    Bad choice. You are "compressing" already compressed files.
    A better choice would be to copy 600 MB from windows "program files" folder, and play with it.
  • eyemaster
    marracoBad choice. You are "compressing" already compressed files.A better choice would be to copy 600 MB from windows "program files" folder, and play with it.

    Bad choice if you're trying to compress file, but not a bad choice if you're just trying to stress a CPU. It will still have to do a whole lot of calculations regardless of the files.
  • b23h
    Thank you very much for this article. It came at the perfect time for me. I’ve just upgraded from a 65 watt AMD Athlon 64 X2 4600 to the AMD Phemon II X3 720. Since I’m running a fanless CPU heatsink (ZEROtherm BTF95) I was concerned that the 95 watts of power of the 720 would be too much for the BTF95. I was planning on underclocking the CPU in order to approximate what I thought the heatsink could handle. However with the help of the article I don’t need to underclock it at all. Using the chart of the 710 I estimated some beginning settings for the 720. While I may be able to further lower the voltages I’ve stressed test my current settings by running a program called the Intel Burn Test plus an immoderate amount of Borderlands.

    The 720 seems to have four p-states. The defaults were 1.25/1.15/1.05/.95 I am currently running the CPU at 1.15/1.125/1.0250/.9 I really haven’t thoroughly stress tested all the possibilities so I expect I may still be able to optimize further P-states one through three.

    The timing of this article was excellent for me and I appreciate all the information I’ve gotten at Tom’s Hardware Guide all these years.
  • volks1470
    Typo! Phenom II X3-X4 720-965 only have 6MB of L3 cache, not 8MB. Not a big deal but for a second there I though the 955 had more L3 cache than my 965.
  • 4ILY45
    melangex3Great Stuff. Keep up the good work. This is the type of review that will keep me coming back. How about throwing in the ever popular 720 BE and the new 620 or 630 just for giggles?

    YES PLEASE!!!! :)
  • shreeharsha
    I still need to sell my intel Pentium 660 system to build a AMD system. I am a AMD fan (converted) stuck with intel processor system.
  • JohnnyLucky
    Thanks for a very informative article that helps put things in perspective.
  • chaitanya_mkin
    Im Telling u AMD wll be the king in HISTORY theres no other name than AMD.
    AMD the BEST
  • chaitanya_mkin
    And this comparision is great for amd users, ofcourse for me tooooo cause im using AMD since 6 years.(my brain is AMD ATHLON X2 6000+ WINDSOR 3.02GHz)
  • arnawa_widagda

    We've updated this article (and the first part) with results from an AM3 motherboard and an Athlon II X4 620. The p-state settings we tested with the Athlon II X4 620 can be found in the first part (along with some power consumption numbers).
  • ohim
    http://it.anandtech.com/IT/showdoc.aspx?i=3784&p=7 , this benchmark cought my attention, while intel loses few performance on Linux, AMD gains almost double the performace ? wtf ?
  • Cespenar
    Many users opted for the Phenom X4 940 to steer away from a motherboard and RAM expense.
    I wonder how one of those rigs would stand up to identical scrutiny.
  • maddy143ded
    this article is nice help to me.
    I was searching for something like this.
    you have tested the Athlons, Athlon II X2/X4, Phenom II X3/X4.
    I would have liked to see some tests for Phenom II X2. as essentially this one is a Deneb with 2 cores disabled and a lower 80W TDP istead of 125W tdp.
    it would have given some idea on how much disabling the cores save us power.
    hope thats included in your next update.
  • TrackSmart
    Question for Tom's: Which Phenom II X4 945 processor did you use? AMD sells a 95W TDP version for almost the same price as the 125W TDP version. If you are interested in powersavings, that's clearly the one to buy. It should offer lower power usage with stock settings. And who knows how low you could take it, since it's a binned part. That would have been worth testing given the negligible price premium (less than $5 typically) compared to the 125W TDP version.