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#1 2016-09-14 15:36:00

ayr0
Member
Registered: 2010-08-12
Posts: 94

Skylake power management linux 4.8

Hi all,

Working on getting power managment sorted out on my Skylake laptop.  With the stock 4.7 kernel, laptop will only go into PC2 (and not any deeper).  I installed linux-mainline-4.8rc6 (from AUR) and to my joy saw that laptop will go down to PC7
However, if I put the laptop to sleep and wake it again, I can no longer reach anything below PC2.

I'm aware of this thread: https://bbs.archlinux.org/viewtopic.php?id=214810
I put SATA in min_power mode, but still nothing deeper than PC2 (on 4.7).  GPU options at this point were simply the default options (and gpu spends most of its time in RC6).  Both cores spend almost all of their time in cc7.

The release notes about rc4 mention "skylake power management fix that came in as part of the
gpu updates".  However playing with intel gpu options in 4.7 doesn't seem to get me anywhere.

What I would like to figure out is
1. Why does sleeping/waking mess up power management in 4.8.  I don't see any anomalies in the system log.  Is there a way to see more detailed info about resuming (specifically info about sata and gpu waking up).  I'm using `journalctl  --system --since=today` to view the log.
2. Why can't I get 4.7 to go below PC2.
3. Is Powertop a reliable way to discern pstates?  Are there other methods?

Last edited by ayr0 (2016-09-14 15:38:43)

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#2 2016-09-15 09:47:43

firekage
Member
From: Eastern Europe, Poland
Registered: 2013-06-30
Posts: 617

Re: Skylake power management linux 4.8

I have a question - your laptop machine, based on Skylake, is maybe I7 with real 4 cores with HyperThreading?

I'm curious about power related topics because i own deskop based on Skylake I7-6700K and i from the beginning not able to use suspend/resume while HT is enabled in bios. After resuming all system is frozen, no logs at all.

Last edited by firekage (2016-09-15 09:47:58)

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#3 2016-09-15 12:58:31

R00KIE
Forum Fellow
From: Between a computer and a chair
Registered: 2008-09-14
Posts: 4,734

Re: Skylake power management linux 4.8

As a starting point run powertop and on the Tunables tab toggle all the "bad" settings and check if you can get into lower package c-states. If you can that means there is something else that is preventing the package from going into deeper c-states.

In my case I had to enable sata power management, for all channels that have connected devices, this allowed the package to go into PC6, then I had to also enable autosuspend for the built-in usb bluetooth card to be able to get into PC7. Even if I toggle all other tunables the package will not go lower than PC7.


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#4 2016-09-15 14:20:18

wast3
Member
Registered: 2012-01-26
Posts: 27
Website

Re: Skylake power management linux 4.8

ayr0 wrote:

3. Is Powertop a reliable way to discern pstates?  Are there other methods?

I'd try i7z

Last edited by wast3 (2016-09-15 14:20:28)

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#5 2016-09-15 16:29:51

ayr0
Member
Registered: 2010-08-12
Posts: 94

Re: Skylake power management linux 4.8

firekage wrote:

I have a question - your laptop machine, based on Skylake, is maybe I7 with real 4 cores with HyperThreading?

I'm curious about power related topics because i own deskop based on Skylake I7-6700K and i from the beginning not able to use suspend/resume while HT is enabled in bios. After resuming all system is frozen, no logs at all.

It's an i5-6300U.  My system suspend/resume is working fine.  It's just that after resuming, the processor can't reach deeper pstates again.

That is interesting about HT.  I didn't know it could interfere with sleep/resume.  I did get constant freezes a few days ago, but tracked that down to bad options for the i915 driver.

wast3 wrote:
ayr0 wrote:

3. Is Powertop a reliable way to discern pstates?  Are there other methods?

I'd try i7z

I'll give that a try, though IIRC, it only gives info on core states, not package states.

R00KIE wrote:

As a starting point run powertop and on the Tunables tab toggle all the "bad" settings and check if you can get into lower package c-states. If you can that means there is something else that is preventing the package from going into deeper c-states.

In my case I had to enable sata power management, for all channels that have connected devices, this allowed the package to go into PC6, then I had to also enable autosuspend for the built-in usb bluetooth card to be able to get into PC7. Even if I toggle all other tunables the package will not go lower than PC7.

All my setting are already good in powertop.  I can see that that the core c-states spend a lot of time in cc7 and that each core individually spends a good chunk of time in C-10SKL.  I'll have to double check the autosuspend (I have bluetooth disabled).
If I use my 4.8rc6 kernel, I can get down to PC6 and PC7 until I sleep.  Upon resume, I'm right back up to PC2.

What kind of hardware do you have on your sata channels?  I have a Sandisk Extreme Pro SSD on my sata channel.  Maybe it's dependent on the type of ssd?

Last edited by ayr0 (2016-09-15 16:48:39)

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#6 2016-09-15 20:32:54

R00KIE
Forum Fellow
From: Between a computer and a chair
Registered: 2008-09-14
Posts: 4,734

Re: Skylake power management linux 4.8

I have a Crucial MX200 SSD on one channel and the other is used by the DVD drive that came with the laptop, according to dmesg it is a PLDS DVD-RW DA8A6SH. The SSD link works at 6.0 Gbps and the DVD drive link works at 1.5 Gbps.


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#7 2016-09-26 19:23:44

ayr0
Member
Registered: 2010-08-12
Posts: 94

Re: Skylake power management linux 4.8

I started playing around with the Linux 4.8 kernel.  With 4.8rc6, I can get PC7, but only until the first suspend/resume cycle.  After resuming, PC2 is the best my laptop can do.  Still no luck with 4.7 kernel

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