I have been interested in the effect of kernel-power v49 on battery usage, particularly with smartreflex enabled, so I ran a few tests to have a rough ideia of its impact.

The system runs CSSU testing, and the test setup was:
* install mplayer and i2c-tools
* enable offline mode
* mute the volume
* turn off the screen just before the test (see below)
The rationale is to control the test scenario and minimize the power consumption of other N900 components, so the test results can better measure the MPU power consumption.

For this test I have chosen playing mp3 files as 'load'.

The test is as follows:
1. read current battery status (with i2cget)
2. play some music files (with mplayer)
3. read current battery status again
4. calculate the diff of 1 and 3
The atual shell code I used in the test is:
The /bin/su is required because mplayer bombs when run as root. During the sleep I turned the screen off.

Warning: i2c-tools is very low level and may damage the hw if used incorrectly.

In my test I used a ~5min mp3 with a 5x loop, which gives about 25-30min of playing.

The results are the following.

| load | nokia kernel | kp49 default | kp49 dsp | kp49 starving |
| mp3 | 165 | 145 | 145 | 154 |
| mp3 | 100% | 88% | 88% | 93% |

Each test has been run at least 3 times and the lower number is presented in the table.

Conclusions for my device with load 'playing mp3,':
* the most power efficient case is kp49 with smartreflex enabled;
* for my device with load 'playing mp3,' overclocking does not save power (the saying goes that overclocking may improve battery usage since code runs faster and processor idles sooner);
* smartreflex is more power efficient than undervolting the processor.

Congratulations to the KP team and, in particular, to those working on SR!

It would be interesting to see more results with other N900s and other loads.

history:
* check post #2 for relevant considerations
* added numbers for 'starving' profile