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

Kai-Heng Feng
2019-07-25T14:02:47Z

Hi Rafael,

at 17:51, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:

> Hi Keith,
>
> Unfortunately,
>
> commit d916b1be94b6dc8d293abed2451f3062f6af7551
> Author: Keith Busch <keith.busch@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.
>
> 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.

Can you please provide the output of `nvme id-ctrl /dev/nvme*` and I’ll
test the NVMe controller on XPS 9380.

Kai-Heng

>
> Cheers,
> Rafael