AMD's Cool'n'Quiet: Disable it

One interesting phenomenon that we encountered during testing on the AMD/NVIDIA platforms with the Phenom series of processors is the effect of Cool’n’Quiet (CnQ) on our BD playback results. We utilized a Phenom 9950BE in our test results today along with the 780G/GF8200/790GX chipsets. When playing back our H.264 title, The Simpsons Movie, with CnQ disabled we noticed an average CPU utilization of 6%~7% with platform power averaging anywhere from 132W to 140W depending on the chipset and motherboard. Video playback was smooth and stutter free on this title and many others regardless of the encoding format utilized.

One of the prime objectives for our HTPC systems is energy saving, especially during playback operation - the idea being that lower power use produces less heat and should therefore also result in a quieter system. The quickest way to reduce platform power on an AMD based system is to enable CnQ. After enabling CnQ in the BIOS and setting our Vista power management profile to balanced or power saver, we noticed our platform power requirements dropped to 99W~112W. This is a 25% or so improvement in power savings so we were naturally pleased with the results.

We fired up Power DVD 8 Ultra, popped The Simpsons Movie back in and decided to see how well the system operated. Our CPU utilization numbers increased to 16%~23%, but considering our processor and lack of background activities, this increase was perfectly acceptable. At least until we sat through this movie and others. We started to notice slight stutters, pauses, and even some judder at various times during the movie. At times, it was very pronounced but other times it was very subtle, but it was not so subtle that we did not notice.

The most frustrating part is that it never occurred in the same section of a title or at the same time. We would notice stuttering in the first 30 seconds of a title at times and other times it would not occur at all. In every case with CnQ enabled, we eventually noticed this behavior, regardless of chipset on the AMD platform. Turning off CnQ resulted in an immediate improvement in our viewing experience. We are investigating this problem (actually it has occurred in the past on the Athlons but not to this extent), but until then our suggestion is leave CnQ off and suffer the consequences of increased power usage. (Or at least, leave it off if you're putting together an HTPC.)

Hardware Blu-ray Decode Acceleration Hardware Accelerated Blu-ray Playback Comparison
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  • duploxxx - Tuesday, October 14, 2008 - link

    nice review, gives a clear ups and downs from each part. there's off course always a reason to recommend an intel part in your conclusion even if you brake it to the ground in the earlier pages....this time you took power consumption, which was one part you would already know from the moment you made your base specs. however for a basic htpc people don't buy quadcores, they buy dual's.

    put a 4850e on the plate against e5200 and start all over again, i'am sure you will get a whole other conclusion and 0 reasons to ever buy a s775 platform for htpc in stead you would pick the nvdia/amd offerings with am2 chipset.
  • npp - Tuesday, October 14, 2008 - link

    I suspect the E5200 system would be faster at the end - running at equal clock speeds Core 2 CPUs tend to faster than the old Athlons (at least I think so). I'm not sure what goes for the power consumption, but I really don't understand why one should care about that, anyway. Decent coolers are all around and saving the planet by cutting off some 20-30-50W from your bill is simply ridiculous. As long as we're talking of numbers around the 100W mark, anything goes.
  • strikeback03 - Tuesday, October 14, 2008 - link

    Anandtech has seemed to favor quad-cores for transcoding duties in past HTPC articles.
  • harshaflibbertigibbet - Tuesday, October 14, 2008 - link

    I hope you will also be reviewing the much delayed and finally launched NVIDIA GeForce 9300/9400 chipsets for the Intel platform. In my opinion, they would end up being the best solution for HTPC users.
  • Badkarma - Tuesday, October 14, 2008 - link

    Hi Gary,

    I read through your article which is very good btw. However, I couldn't find what driver versions you were using to test with. Sorry if I just missed it.
  • Golgatha - Tuesday, October 14, 2008 - link

    I have a HTPC running an Intel E8400 C2D, Zalman 9500 HSF, 6GB RAM, a passively cooled ATI 2600 Pro 256MB, Lite-On SATA Blu-ray/HD DVD combo optical drive, Abit IP35-E, 3 hard drives (250GB and 2x750GB), 380w Earthwatts PS, 4 fans (this includes the PS and CPU fan), and a HT Omega Striker 7.1 discreet sound card. The system runs Vista 64bit Home Premium.

    My requirements for a HTPC were for it to be out of sight (tucking it behind the entertainment center and using a Bluetooth Logitech DiNovo Mini works great for me), run cool and quiet, and not use much electricity. Running 2xFolding@Home clients, a Tversity server for my PS3, and playing a Blu-ray movie uses about 115w system power for the entire system (measured with a kill-a-watt brand device).

    I think the configurations tested weren't really representative of how folks build their HTPC, unless you're assuming it's a do-it-all type of PC, which isn't really a HTPC at that point IMO?
    Why in the world would a dedicated HTPC need a quad core CPU or a 520w PSU? Dual core 45nm parts are more than capable of even the most demanding tasks. Also, a 520w PSU for a 100-150w system is completely inefficient.">

    Also, barebones motherboards are cheaper than their IGP counterparts by at least $15-$20 (my Abit board was $70 after MIR), which gives a bit of leeway to purchase a $30-$50 dedicated video card that will give a much better end user experience at the end of the day. Also, when something better comes out (hey, I'm interested in AMD's new 4550 etc. series too), you don't have the unnecessary components on the motherboard sucking electricity.
  • fic2 - Tuesday, October 14, 2008 - link

    That is exactly what I don't understand about the recent "HTPC" articles on here. For some reason they think that people actually use quad monster processors for HTPCs. I got a $25 BE-2400 45W cpu that I intend to use in an HTPC, not some 125W beasty thing that triples my power usage.
  • androo - Wednesday, October 15, 2008 - link

    I totally agree! HTPCs are for the living room and should make little to no noise. 140W CPUs have no place in such a rig. Save that for a gaming rig that goes in the bedroom or den (especially if your wife is a light sleeper!).
  • tonyintoronto - Wednesday, October 15, 2008 - link

    I don't get it either. HTPC in my opinion are to be low power systems, dedicated to movies, music and TV... Doesn't make any sense to me to see 3x and quad cores tested. I use a AMD 4450E and i'm already way "oversized", that processor can play all formats of HD running at 1.1GHZ w/out any issues together with a cheap asus 3450 card. That and the gaming performance, who in they right mind would game with integraded graphics? its like showing to 1/4 mile race with a horse and carriage.
    I do agree with them, the 780G and G45 are poor excuses for HTPC boards, IMHO the cheapest possible board with ati 4650 or 4670 makes the most sense. Don't get me started on those 550W power supplies :)
  • Mathos - Wednesday, October 15, 2008 - link

    No idea why they used quad core, other than the fact that a quad would spend more time in low power mode and have lower CPU usage than a dual. That and there are no AMD dual cores out yet that use HT 3.0, although the x2 6500 should be. Most of the AMD based boards are adversely effected by using an older X2 instead of something that uses HT3.0.

    Anyone not seeing the point of a 780g/790gx board, or an nForce 8200/8300 board for an HTPC is not thinking. The point is to not need a discrete card. Many HTPC's use low profile cases, which make finding an adequate video card difficult. Not to mention with the 780g/790gx you can later install a $50 discrete 3650 or 3450 and run it in Xfire with the IGP for better gaming performance. Same goes for the lower end 8000 and 9000 cards on the nforce chipset.

    As far as the PSU goes it leaves room for possibly adding in a discrete card later. Also remember that most PSU's are most effecient at around 50% load which happens on some of the AMD systems under heavy load. Not to mention if you want to have a silent PSU you need to keep the load low so the fan isn't humming constantly, which would happen on a lower rated PSU.

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