[personal profile] mjg59
(Edit to add: this issue is restricted to the mobile SKUs. Desktop parts have very different power management behaviour)

Linux 4.5 seems to have got Intel's Skylake platform (ie, 6th-generation Core CPUs) to the point where graphics work pretty reliably, which is great progress (4.4 tended to lose all my windows every so often, especially over suspend/resume). I'm even running Wayland happily. Unfortunately one of the reasons I have a laptop is that I want to be able to do things like use it on battery, and power consumption's an important part of that. Skylake continues the trend from Haswell of moving to an SoC-type model where clock and power domains are shared between components that were previously entirely independent, and so you can't enter deep power saving states unless multiple components all have the correct power management configuration. On Haswell/Broadwell this manifested in the form of Serial ATA link power management being involved in preventing the package from going into deep power saving states - setting that up correctly resulted in a reduction in full-system power consumption of about 40%[1].

I've now got a Skylake platform with a nice shiny NVMe device, so Serial ATA policy isn't relevant (the platform doesn't even expose a SATA controller). The deepest power saving state I can get into is PC3, despite Skylake supporting PC8 - so I'm probably consuming about 40% more power than I should be. And nobody seems to know what needs to be done to fix this. I've found no public documentation on the power management dependencies on Skylake. Turning on everything in Powertop doesn't improve anything. My battery life is pretty poor and the system is pretty warm.

The best thing about this is the following statement from page 64 of the 6th Generation Intel ® Processor Datasheet for U-Platforms:

Caution: Long term reliability cannot be assured unless all the Low-Power Idle States are enabled.

which is pretty concerning. Without support for states deeper than PC3, Linux is running in a configuration that Intel imply may trigger premature failure. That's obviously not good. Until this situation is improved, you probably shouldn't buy any Skylake systems if you're planning on running Linux.

[1] These patches never went upstream. Someone reported that they resulted in their SSD throwing errors and I couldn't find anybody with deeper levels of SATA experience who was interested in working on the problem. Intel's AHCI drivers for Windows do the right thing, but I couldn't find anybody at Intel who could get any information from their Windows driver team.

My mobile part is seeing pc8

Date: 2016-04-13 10:42 pm (UTC)
From: (Anonymous)
This is a Dell Precision 5510
model name : Intel(R) Xeon(R) CPU E3-1505M v5 @ 2.80GHz

          Package   |             Core    |            CPU 0       CPU 4
                    |                     | C0 active   2.2%        0.2%
                    |                     | POLL        0.0%    0.0 ms  0.0%    0.0 ms
                    |                     | C1E-SKL     0.4%    0.3 ms  6.4%    2.9 ms
C2 (pc2)   39.7%    |                     |
C3 (pc3)    1.0%    | C3 (cc3)    0.2%    | C3-SKL      0.5%    0.2 ms  0.0%    0.0 ms
C6 (pc6)    8.7%    | C6 (cc6)   17.4%    | C6-SKL     12.2%    0.9 ms  8.6%   20.1 ms
C7 (pc7)    0.0%    | C7 (cc7)   64.2%    | C7s-SKL     0.0%    0.0 ms  0.0%    0.0 ms
C8 (pc8)   21.7%    |                     | C8-SKL     65.6%    1.8 ms  4.1%    2.7 ms
C9 (pc9)    0.0%    |                     | C9-SKL      0.0%    0.0 ms  0.0%    0.0 ms
C10 (pc10)  0.0%    |                     | C10-SKL    13.6%    6.3 ms 78.5%   25.2 ms

Re: My mobile part is seeing pc8

Date: 2016-04-14 07:29 am (UTC)
From: [personal profile] mikesart
I've got a Dell XPS 9350 laptop, and if powertop is telling the truth and I'm reading it correctly, it's doing c7 as well. Although my gpu is currently pegged at 100% since I'm still running kernel 4.5 w/ i915.enable_rc6=0 to workaround the gpu bug.

powertop and lscpi -vvv details here:

http://pastebin.com/vBu5pBq6

I've been shutting it down completely when not in use and this post has certainly convinced me to continue doing that.

Re: My mobile part is seeing pc8

Date: 2016-04-14 07:48 am (UTC)
From: (Anonymous)
Same for me.

Dell XPS 15 9550, Intel(R) Core(TM) i7-6700HQ CPU @ 2.60GHz

Re: My mobile part is seeing pc8

Date: 2016-04-19 12:11 pm (UTC)
From: (Anonymous)
If you happen to follow up can you give some details on your kernel and any configuration you did?

Re: My mobile part is seeing pc8

Date: 2016-08-11 01:19 am (UTC)
From: (Anonymous)
I have the same Chip i.e : http://ark.intel.com/products/89608/Intel-Xeon-Processor-E3-1505M-v5-8M-Cache-2_80-GHz - which seems to be the same architecture as the 6th Gen U and Y processors. (Despite Matthews edit, these do count amongst those effected)

I am currently running a 4.7 kernel on ubuntu 16.10 with some tlp tweaks. So whatever patches were in 4.7 they don't solve the issues for skylake.

P-states sits in c2 or c3 disabling ntel pstates and using acpi with conservative governor I have seen it in c7. But this means you don't get the boost states/higher frequency clocks. i.e 8k - 2.81k hz only when using ACPI without pstates module. The machine runs cool and well when using the acpi module rather than the pstates. i.e with the following kernel line:

pcie_aspm=force intel_pstate=disable drm.vblankoffdelay=1 i915.semaphores=1 i915_enable_rc6=1 i915_enable_fbc=1


I am using HP Zbook studio g3 with latest bios N82 Ver. 01.13 from the first of August. NVME and Sata drives.

I've had some weird issues include sound disappearing from Windows randomly, and squeeling beeps during post after a hard reset due to crash.

lshw for those interested :

aenertia@hurapaki:~$ sudo lshw
[sudo] password for aenertia:
hurapaki
description: Notebook
product: HP ZBook Studio G3 (M6V81AV)
vendor: HP
serial: #
width: 64 bits
capabilities: smbios-2.7 dmi-2.7 vsyscall32
configuration: administrator_password=disabled boot=normal chassis=notebook family=103C_5336AN frontpanel_password=disabled keyboard_password=disabled power-on_password=disabled sku=M6V81AV uuid=#
*-core
description: Motherboard
product: 80D4
vendor: HP
physical id: 0
version: KBC Version 11.62

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Matthew Garrett

About Matthew

Power management, mobile and firmware developer on Linux. Security developer at Google. Ex-biologist. @mjg59 on Twitter. Content here should not be interpreted as the opinion of my employer.

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