AMD's K6-2+ in Notebooks - Evaluating Performance with PowerNow

The Test

The test platform we used was the Hewlett Packard Pavilion N3370, the notebook was left in its original configuration with the following exceptions:

• The 64MB PC100 SDRAM SO-DIMM was replaced with a 128MB PC100 SDRAM SO-DIMM. The resulting performance increase was approximately 13%, and definitely worth the investment for current notebook users with only 64MB of memory. Adding the larger SO-DIMM did not noticeably effect battery life.
• The factory hard drive was formatted and we installed only the applications and benchmarks we needed to conduct our tests.

To measure performance we made use of ZD's Battery Mark 4.0, BAPCo's SYSMark 2000 and MadOnion's Video2000 benchmark suites. Battery Mark is an interesting way of measuring battery life because it actually simulates real world usage, including pauses between tasks in which case a technology such as PowerNow! would help quite a bit. In the real world, we're never constantly working on a particular task, there are always points where the user pauses and the CPU has to sit there and eat up valuable clock cycles.

Battery Performance

Of course the first question we asked ourselves upon learning of PowerNow! a while back was "how effective is it?" In the above chart you can see the effects of the three different power management modes provided by PowerNow!

The Max Performance bar in the chart is the equivalent of not having PowerNow! at all since the CPU is always running at 550MHz. As you can see, without any sort of power management, the 550MHz K6-2+ which is pulling in 18W of power is definitely draining the battery pretty hard under normal usage. With a battery life of just 2 hours and 7 minutes, you can watch a DVD but that's pretty much it, you had better be carrying some spare batteries on you.

The Max Battery Life setting obviously yields the longest battery life of 174 minutes, that's almost 3 hours. While this particular laptop didn't have a spectacular battery life to begin with, an improvement of 37% over what a normally clocked laptop would offer is impressive. However, in this Max Battery Life setting the CPU is only operating at 200MHz, meaning that you take a huge performance hit in order to gain that extra hour of battery life. Notebook manufacturers have been doing things like this for quite some time now, even before the advent of Speedstep and PowerNow!. Most notebooks have an option for the system to optimize itself for battery life which often times results in the system simply disabling the L2 cache among other things. This is fine if you're not doing any complex tasks, but if you are, then the next setting may be a bit more attractive.

As we just learned, putting the system into PowerNow! Automatic mode allows for the dynamic adjustment of the CPU speed and voltage supplied to the processor depending on the needs of the applications being run. And simply by enabling this mode we get an instant gain of almost 30 minutes of battery life. This converts into a 21% increase in battery life with a theoretically very small drop in performance, we will be investigating the validity of that theory next.