mjg59 | Skylake's power management under Linux is dreadful and you shouldn't buy one until it's fixed

(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.

Flat | Top-Level Comments Only

FYI: Since EFI can directly run Portable Executables (.exe) you can just drop the .exe from your vendor in your EFI system partition and run it from the EFI menu, no need to boot windows. I've done this on my Dell XPS 13 system multiple times now.

That's a thing you can do? I've been digging everywhere on ways to install UEFI updates on this thing, and it hasn't come up. Not that I'm disbelieving you, it just seems amazingly poorly documented. And it's the same EXE update files they have for Windows?

Dell's firmware update binaries are very magic.

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.)

Lenovo provides CD images, that boots and flash firmware without windows.
https://download.lenovo.com/pccbbs/mobiles/n1gur08w.txt

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

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 2016-05-09 20:36 (UTC)

There was a new UEFI update for the laptop released a few days ago. Windows install only. So after going to the trouble of installing Windows 10 to an external USB drive to boot off of and run the update (I really didn't feel like repartitioning the drive or having to image and restore it) that actualy worked to do the update.

But it's still 0x74 microcode. (facepalm)

On the XPS 13, how are you dropping into the efi shell to execute these?
I always imagined they'd have windows software that would hamper this, even if it can run .exe

can you write/share a relevant tutorial for this process, as I will need to do this until Dell publishes the files for fwupdate.

in this generation:
xps 9350: https://secure-lvfs.rhcloud.com/lvfs/device/33773727-8ee7-4d81-9fa0-57e8d889e1fa
precision 5510: https://secure-lvfs.rhcloud.com/lvfs/device/124c207d-5db8-4d95-bd31-34fd971b34f9

Otherwise put the .EXE from support.dell.com on a FAT32 USB key or on the ESP and select flash BIOS from the F12 POST menu.

Thank you,

I found instructions for flashing the .exe, but you gave me .cab files. How can I flash .cabs?

Can still do the .exe method on the 9350?

Just hit F12 at boot and choose "BIOS Update" from the menu.

I found what he's talking about. It's on the Arch wiki for the curious

http://hgdev.co/install-bios-update-under-linux-on-the-dell-xps-13-9343-2015/

I'll have to try this on my 9350 when I get it tomorrow.
Does anyone know how I can check the microcode version?

9350 has updates at LVFS that can be applied as capsules.
https://secure-lvfs.rhcloud.com/lvfs/device/33773727-8ee7-4d81-9fa0-57e8d889e1fa

Skylake's power management under Linux is dreadful and you shouldn't buy one until it's fixed

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