[Bug 364554] [NEW] conservative cpugovernor only does one increment

[Johan Ehnberg]

Public bug reported:

Tested in Jaunty on my Phenom II X4 810 (800/1400/1900/2600 MHz).

My use case: I want to run boinc and still save power by keeping the cpu at lowest clock speed while only load is boinc. When I do something like archiving with gzip, I want all the power I can get. To accomplish this, I need the following things:
- conservative governor (ondemand is too jumpy, reacting on the slightest demand on the same core as boinc)
- ignore nice loads enabled (to separate boinc from other processes like gzip)

So far everything was easy, I chose the governor and set the ignore_nice_load flag in /sys. Boinc did not cause the clock speed to change. However, neither did any other programs like gzip:
cat /dev/urandom |gzip > /dev/null

After investigating this, I noticed that changing the freq_step to a higher value from the default 5 would result in more expected behaviour.
echo 25 > freq_step

However, the frequency now would land at 1900 MHz and stay there, when
I'd expect it to change up to 2600 MHz after a while). Changing the
above value to 30 or more would cause it to immediately change to 2600
MHz. It changes back to 800 MHz when gzip quits.

For me this variant is acceptable, I expect to always want either
powersave or performance, never the middle steps, while still not
wasting idle time. However, as far as I can understand, the test shows
that the default increment does nothing which is a problem because the
governor only seems to do one increment up or down.

(The same behaviour applies for the inverse scenario. If the CPU was
manually set to 2600 MHz and 5 freq_step before choosing conservative,
it does not change down.)

Linux shadoweel 2.6.28-11-generic #42-Ubuntu SMP Fri Apr 17 01:58:03 UTC 2009 x86_64 GNU/Linux
Ubuntu 2.6.28-11.42-generic

** Affects: linux-meta (Ubuntu)
     Importance: Undecided
         Status: New

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conservative cpugovernor only does one increment
https://bugs.launchpad.net/bugs/364554
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