[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.

Nasty issues with Linux 4.2, Skylake and NVMe

Date: 2016-04-13 10:06 pm (UTC)
From: (Anonymous)
Until Linux Mint 18 will be released I thought it would be OK to go with the current release - 17.3. It's OK most of the time, until it breaks in various ways.

Mainboard: ASUS Z170-DELUXE
CPU: Intel Core i3-6320 3.90 GHz (Skylake)
SSD: Samsung 950 Pro 256GB M.2
Linux kernel: 4.2.x

Trying kernel 4.4 (available from Ubuntu) renders an unbootable system due to some strange issues configuring GRUB I think - I just didn't have the time to investigate in detail, although I tried chrooting and updating grub from a live session, without success.

I might as well consider another distro if kernel 4.5 or newer fixes these issues. Sometimes the system freezes so badly not even the (hardware) reset button doesn't work. Other times the NVMe controller simply throws in the towel [1] and I get left with some partially running programs, everything running from RAM, because the storage disappears until I reset the PC.

It's been two and a half terrible months since I got this new PC and lacking the time to find out answers it's frustrating I have no idea who to blame. So I guess I might as well blame myself for going with "the latest and greatest" from Intel without properly researching compatibility.

[1] http://pastebin.com/2djDSh3m
From: (Anonymous)
I had the same issue, you can resolve it by adding `nvme` to `/etc/initramfs-tools/modules` and then running `sudo update-initramfs -u`. While this works, I found that because of incompatibilities with mesa and the kernel, a lot of video glitches occur even at 4.5.


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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