Dear Richard Hughes, I'm running Debian Testing with upower version 0.9.17. I've looked been searching to reduce the power consumption of my laptop for a long time now, and upowerd appears to write to disk a large amount in comparison to other daemons. I've found the code responsible, in up-history.c. The program is compiled to save the power usage statistics in /var/lib/upower/* every ten minutes, and to keep a week's worth of data. For my computer this amounts to 800KB of data. That adds up to be in excess of 100MB written/day!
Although I recognize that this is not likely to have a significant effect in itself, when compounded with disk encryption, full disk backups, a small SSD or a heavy-disk use server this will cause a noticeable effect. I regret that I do not have the skills to submit a patch, but I'd like to express my concerns nonetheless. Please consider editing your save function to write only the latest changes to these files. Baring that, consider letting the save frequency be changed as a variable in /etc/UPower/UPower.conf. This is certainly a desired feature, as shown by bug http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=641845 I see that when first designed, upowerd saved statistics every five seconds. Your present choice of ten minutes is a much saner value. However, if not technically impossible, I strongly suggest you add a user config for this setting. I have measured this >100MB/day disk write behavior using the iotop command utility with the -P and -a options. whatever the present size of all the files in /var/lib/upower/ can be observed being written every ten minutes. Apart from this, I'd like to compliment you all on this stable utility. I've learned a lot about UPower. I plan to save all my power statistics logs for future analysis from now on, as I find power usage interesting. I have also personally enjoyed your blog and made use of the information about colord on it - Thanks! Sincerely, Stuart Miller
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