Profiling Power Consumption on Android

Profiling Power Consumption on Android

Over the past couple of days, I have been trying to figure out a painless method for collecting energy performance on Android mobile phones. I was really happy to discover that my Galaxy Nexus phone reports power events using ftrace. Moreover, cpu_idle reports the time time spent in each low-power state using sysfs. To capture the time spent in each state, it is just a matter of reading a few files. Pretty sweet.

Since both methods seemed so easy to implement, I ended up implementing it both ways: compute the time spent in each c-state using ftrace (sum up the reported c-state residency) and via the results reported in sysfs. To my surprise, the two results did not match --- if fact they were nowhere close to similar.

While the jury is not yet out, it seems like the difference between the reported statistics are due to the state coupling that is necessary so that the two cores of OMAP to enter the low power state. The following mails seem to validate this hypothesis:

• http://comments.gmane.org/gmane.linux.ports.arm.omap/77416

Below are some notes on tools:

Systrace:

• http://developer.android.com/tools/help/systrace.html
• The systrace produced by systrace tool on android calls the ftrace function. You can find the format at http://www.mjmwired.net/kernel/Documentation/trace/ftrace.txt

# tracer: function
#
#           TASK-PID   CPU#    TIMESTAMP  FUNCTION
#              | |      |          |         |
            bash-4251  [01] 10152.583854: path_put <-path_walk class="l" span="">

bash-4251 [01] 10152.583855: dput <-path_put class="l" span=""> bash-4251 [01] 10152.583855: _atomic_dec_and_lock <-dput pre="">
The time is in the format .

CPUFreqUtils:

Very nice description of linux support for power consumption:
http://doc.opensuse.org/products/draft/SLES/SLES-tuning_sd_draft/cha.tuning.power.html#sec.tuning.power.tools.cpufrequtils

The cpuidle subsystem controls when a system goes to sleep. A description of the system can be found here. The nice part of cpuidle is that it exports a ton of important events on sys-fs. A complete description can be found here.

http://lwn.net/Articles/473072/
http://comments.gmane.org/gmane.linux.ports.arm.omap/77416
http://scape.cs.vt.edu/wp-content/uploads/2012/08/ITJ12_Android_Energy-Aware.pdf

References:

1. Galaxy Nexus Hardware
2. Cortex-A9 Power Management

Camera Ready

Creating the camera ready version of papers is a nuisance. Today, I spend 2 hours to try to conform with all the requirements of an IEEE journal. Some of the frustrating aspects have to deal with the fact that they want to all images in EPS format and, as a mac user, I used pdf. It is easy to convert all the pdf to eps using pdftops. You can use the below find command to covert all files in a directory:

find . -name "*.pdf"  -exec pdftops -eps {} \;

The other difficulty was related doflattening the tex files and including the bibliography rather than the bib file. So I would not have to deal with this nonsense again, I wrote a short script to do this for me. I hope to expand this in the future to also handle the renaming of the figures in order of appearance; but for now that remains a manual step. The scrip is attached to the end this post