The IGP Chronicles Part 2: AMD 780G vs. Intel G45 vs. NVIDIA GeForce 8200by Gary Key on October 14, 2008 12:40 PM EST
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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.)