[Regression] Commit "nvme/pci: Use host managed power state for suspend" has problems

[kai.heng.feng@canonical.com (Kai-Heng Feng)]

at 01:03, Rafael J. Wysocki <rafael@kernel.org> wrote:

> On Thu, Jul 25, 2019@6:24 PM <Mario.Limonciello@dell.com> wrote:
>> +Rajat
>>
>>> -----Original Message-----
>>> From: Kai-Heng Feng <kai.heng.feng at canonical.com>
>>> Sent: Thursday, July 25, 2019 9:03 AM
>>> To: Rafael J. Wysocki
>>> Cc: Keith Busch; Christoph Hellwig; Sagi Grimberg; linux-
>>> nvme at lists.infradead.org; Limonciello, Mario; Linux PM; LKML
>>> Subject: Re: [Regression] Commit "nvme/pci: Use host managed power  
>>> state for
>>> suspend" has problems
>>>
>>>
>>> [EXTERNAL EMAIL]
>>>
>>> Hi Rafael,
>>>
>>>@17:51, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
>>>
>>>> Hi Keith,
>>>>
>>>> Unfortunately,
>>>>
>>>> commit d916b1be94b6dc8d293abed2451f3062f6af7551
>>>> Author: Keith Busch <keith.busch at intel.com>
>>>> Date:   Thu May 23 09:27:35 2019 -0600
>>>>
>>>>     nvme-pci: use host managed power state for suspend
>>>>
>>>> doesn't universally improve things.  In fact, in some cases it makes
>>>> things worse.
>>>>
>>>> For example, on the Dell XPS13 9380 I have here it prevents the  
>>>> processor
>>>> package
>>>> from reaching idle states deeper than PC2 in suspend-to-idle (which, of
>>>> course, also
>>>> prevents the SoC from reaching any kind of S0ix).
>>>>
>>>> That can be readily explained too.  Namely, with the commit above the
>>>> NVMe device
>>>> stays in D0 over suspend/resume, so the root port it is connected to  
>>>> also
>>>> has to stay in
>>>> D0 and that "blocks" package C-states deeper than PC2.
>>>>
>>>> In order for the root port to be able to go to D3, the device connected
>>>> to it also needs
>>>> to go into D3, so it looks like (at least on this particular machine,  
>>>> but
>>>> maybe in
>>>> general), both D3 and the NVMe-specific PM are needed.
>>
>> Well this is really unfortunate to hear.  I recall that with some disks  
>> we were
>> seeing problems where NVME specific PM wasn't working when the disk was  
>> in D3.
>>
>> On your specific disk, it would be good to know if just removing the  
>> pci_save_state(pdev)
>> call helps.
>
> Yes, it does help.
>
>> If so, :
>> * that might be a better option to add as a parameter.
>> * maybe we should double check all the disks one more time with that  
>> tweak.
>
> At this point it seems so.
>
>>>> I'm not sure what to do here, because evidently there are systems where
>>>> that commit
>>>> helps.  I was thinking about adding a module option allowing the user to
>>>> override the
>>>> default behavior which in turn should be compatible with 5.2 and earlier
>>>> kernels.
>>>
>>> I just briefly tested s2i on XPS 9370, and the power meter shows a  
>>> 0.8~0.9W
>>> power consumption so at least I don?t see the issue on XPS 9370.
>>
>> To me that confirms NVME is down, but it still seems higher than I would  
>> have
>> expected.  We should be more typically in the order of ~0.3W I think.

 From what I?ve observed, ~0.8W s2idle is already better than Windows (~1W).
0.3W is what I see during S5.

>
> It may go to PC10, but not reach S0ix.
>
> Anyway, I run the s2idle tests under turbostat which then tells me
> what has happened more precisely.

The XPS 9370 at my hand does reach to s0ix during s2idle:
# cat /sys/kernel/debug/pmc_core/slp_s0_residency_usec
15998400

So I think keep the root port in D0 is not the culprit here.
Maybe something is wrong on the ASPM settings?

Kai-Heng