[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.

Re: EFI updates

Date: 2016-04-14 09:19 am (UTC)
From: [personal profile] gourdcaptain
Ah then that's probably not going to fly with the Lenovo ones. (In my defender for buying it, finding good 11 inch laptops these days is hard- netbooks have mostly died out in favor of tablets and such. Plus, I needed Skylake for hardware HEVC decoding since nothing in the relatively cheap laptop range is going to have a discrete card that can do that, and 1080p HEVC takes a fair chunk of CPU to decode.)

Re: EFI updates

Date: 2016-04-15 06:34 am (UTC)
From: (Anonymous)
Lenovo provides CD images, that boots and flash firmware without windows.
https://download.lenovo.com/pccbbs/mobiles/n1gur08w.txt

Re: EFI updates

Date: 2016-04-15 07:29 am (UTC)
From: [personal profile] gourdcaptain
Yeah, that's for a model that cost twice as much as the dinky little thing I'm using right now. I'm not seeing one listed for the Yoga 700 11-inch: http://support.lenovo.com/us/en/products/Laptops-and-netbooks/Yoga-Series/yoga-700-11isk?linkTrack=Homepage:Body_Search%20Products&beta=false

Re: EFI updates

Date: 2016-05-01 07:43 am (UTC)
From: [personal profile] gourdcaptain
Just to make google searches for this a bit more helpful, some experimentation later seems to link these random boot crashes to the i2c bus going funky when a bunch of stuff tries to hit it all at once during boot: https://bugzilla.kernel.org/show_bug.cgi?id=105251

Doing a weird workaround involving delaying loading hid_multitouch seems to cut down the boot failures by a fair amount: https://bugzilla.redhat.com/show_bug.cgi?id=1297188#c13
(NOTE: Still seem to happen a fair amount, did some statistical testing but still might be the placebo effect.)
Edited Date: 2016-05-09 08:36 pm (UTC)

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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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