Arch Linux

jiba

Member

Registered: 2014-03-08

Posts: 1

Package C7 state (PC7) disabled after suspend-to-disk

Hello,

I'm trying to optimize power management on my laptop (a Thinkpad Yoga with an Intel core i7 Haswell processor), but I discovered a strange behavior involving PC7 state after suspend-to-disk. I'm using the lastest Arch Linux kernel 3.13, but I also had this problem a few days ago with 3.12.

I've added the following parameters to the kernel command line :

pcie_aspm=force i915.i915_enable_rc6=3 i915.i915_enable_fbc=1 i915.lvds_downclock=1

and I set the PCIE policy to powersave at boot time with :

echo powersave > /sys/module/pcie_aspm/parameters/policy

With this configuration, the processor goes up to the package C7 state (PC7) when idling (which is a state with a very low power consumption, possibly the lowest power consumption possible in "normal" usage). This can be verified with the "turbostat" software (%pc7 below) :

cor CPU    %c0  GHz  TSC SMI    %c1    %c3    %c6    %c7 CTMP PTMP   %pc2   %pc3   %pc6   %pc7   %pc8   %pc9  %pc10  Pkg_W  Cor_W GFX_W
          0.60 2.95 2.39   0   0.93   0.04   0.03  98.40   37   37  23.95   0.94   7.03  64.73   0.00   0.00   0.00   1.30   0.07  0.00
  0   0   0.75 2.96 2.39   0   0.53   0.07   0.04  98.61   37   37  23.95   0.94   7.03  64.73   0.00   0.00   0.00   1.30   0.07  0.00
  0   1   0.13 2.77 2.39   0   1.15
  1   2   0.51 2.94 2.39   0   1.27   0.01   0.01  98.19   37
  1   3   1.01 2.98 2.39   0   0.77

However, after a suspend-to-disk and a resume, the PC7 state is not longer used, even when the computer is completely idling :

cor CPU    %c0  GHz  TSC SMI    %c1    %c3    %c6    %c7 CTMP PTMP   %pc2   %pc3   %pc6   %pc7   %pc8   %pc9  %pc10  Pkg_W  Cor_W GFX_W
          0.72 1.80 2.39   0   1.42   0.18   0.10  97.58   41   41  22.03  73.25   0.00   0.00   0.00   0.00   0.00   2.05   0.04  0.00
  0   0   1.96 1.80 2.39   0   1.08   0.24   0.13  96.60   41   41  22.03  73.25   0.00   0.00   0.00   0.00   0.00   2.05   0.04  0.00
  0   1   0.02 1.80 2.39   0   3.01
  1   2   0.80 1.80 2.39   0   0.45   0.11   0.08  98.57   40
  1   3   0.12 1.80 2.39   0   1.13

Additionally, changing /sys/module/pcie_aspm/parameters/policy has no effect.

Finally, if I reboot the computer, or if I suspend-to-RAM (even after a suspend-to-disk), PC7 state is activated again.

Do you have an idea of what is wrong ? As far as I know, suspend-to-disk is close to a full reboot, with the RAM saved to the disk, so how the results can differ after reboot and suspend-to-disk ?

CharlieBra7o

Member

Registered: 2014-03-01

Posts: 23

Re: Package C7 state (PC7) disabled after suspend-to-disk

However, after a suspend-to-disk and a resume, the PC7 state is not longer used, even when the computer is completely idling :
[...]
Finally, if I reboot the computer, or if I suspend-to-RAM (even after a suspend-to-disk), PC7 state is activated again.

I dont understand your second sentence... Did you somehow manage to activate it again or not?

In case you got a Haswell CPU please check out this thread as it addresses a similar issue: Haswell-System doesn't go into powerstates lower than pc3