pm-utils: readahead and journal-commit waste power
Bug #900923 reported by
Tim Gardner
This bug affects 2 people
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
pm-utils |
Confirmed
|
Medium
|
|||
pm-utils (Ubuntu) |
Fix Released
|
Medium
|
Martin Pitt | ||
Precise |
Fix Released
|
Medium
|
Martin Pitt |
Bug Description
Discussion in https:/
Related branches
Changed in pm-utils (Ubuntu Precise): | |
milestone: | none → precise-alpha-2 |
assignee: | nobody → Canonical Foundations Team (canonical-foundations) |
status: | New → Confirmed |
tags: | added: battery-power-consumption |
Changed in pm-utils: | |
importance: | Unknown → Medium |
status: | Unknown → Confirmed |
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Since the posting was on a private list, I'm putting a link into the results and spreadsheet data that covers the analysis:
Results: http:// zinc.canonical. com/~cking/ power-benchmark ing/pm- utils-results/ results. txt zinc.canonical. com/~cking/ power-benchmark ing/pm- utils-results/ pm-tests. ods
Data: http://
== Journal-commit ==
script: power.d/ journal- commit
For ext3/ext4 file systems this sets the journal commit time to 600
seconds(!) when on battery power.
Test: build busybox
Results: NO power savings on HDD drives, with biggest loss of 1.5% on
SSD based netbook.
Recommendation: We remove this script for two reasons:
1) It is shown not to save power on a busy system
2) It is a dangerous option - pushing the commit timeout to 10 minutes
increases the likely of filesystem errors on a system hang.
== Readahead ===
script: power.d/readahead
This script tries to trade off the number of times we spin up a drive to
read for potentially wasted cache. For AC power, set to 256KB, for battery
power, set to 3072KB.
Test: build busybox
Results: All systems fail to show any power savings, in fact SSD loses
~1.7% more power with this enabled.
Recommendation: Remove this script
Please refer to the pm-tests.ods for the results from some thorough testing on 3 representative machines.