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I have a Dell XPS 13 2015 laptop (Broadwell i7) using the intel_pstate
driver for CPU power management. After a cold boot, the CPUs are all
using the "powersave" cpufreq governor:

$ cat /sys/devices/system/cpu/cpu{0..3}/cpufreq/scaling_governor
powersave
powersave
powersave
powersave

However, following a suspend/resume cycle (e.g. by closing and opening the lid), the secondary CPUs end up in
"performance" state:

$ cat /sys/devices/system/cpu/cpu{0..3}/cpufreq/scaling_governor
powersave
performance
performance
performance

This has the undesirable effect of forcing /sys/devices/system/cpu/intel_pstate/min_perf_pct to 100, pegging all of the CPUs
at ~3.2Ghz and hosing the battery life of the system. I would expect the governor setting to persist across the suspend on all cores. Manually setting the secondary cores back to the "powersave" governor resolves the issue.

There does appear to be a known kernel issue in this area (although it
doesn't sound exactly the same):

  https://www.mail-archive.com/linux-
kernel@xxxxxxxxxxxxxxx/msg996192.html

I backported the supposed fix and the issue remained (but note that the
backport is a PITA and I ended up pulling in most of the intel_pstate
changes queued in linux-next). I'm currently working around the issue by
compiling out the "performance" governor entirely.

I didn't have this problem with 15.04, but reverting to the vivid 3.19-based kernel breaks resume entirely with wily userspace, so
it's hard to tell exactly what is responsible. pm-utils has some scripts to poke around at the cpufreq governor, but I commented
all that out and didn't see any change in behaviour.

Any ideas?

--->8

$ lsb_release -rd
Description:	Ubuntu 15.10
Release:	15.10

$ apt-cache policy linux-image-4.2.0-16-generic 
linux-image-4.2.0-16-generic:
  Installed: 4.2.0-16.19
  Candidate: 4.2.0-16.19
  Version table:
 *** 4.2.0-16.19 0
        500 http://gb.archive.ubuntu.com/ubuntu/ wily/main amd64 Packages
        100 /var/lib/dpkg/status

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: Confirmed

-- 
Secondary CPUs switch to "performance" cpufreq following suspend/resume cycle
https://bugs.launchpad.net/bugs/1512153
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