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

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Date:   Thu, 25 Jul 2019 18:59:59 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Keith Busch <keith.busch@...el.com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        linux-nvme <linux-nvme@...ts.infradead.org>,
        Mario Limonciello <Mario.Limonciello@...l.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Regression] Commit "nvme/pci: Use host managed power state for
 suspend" has problems

On Thu, Jul 25, 2019 at 4:02 PM Kai-Heng Feng
<kai.heng.feng@...onical.com> wrote:
>
> Hi Rafael,
>
> at 17:51, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>
> > Hi Keith,
> >
> > Unfortunately,
> >
> > commit d916b1be94b6dc8d293abed2451f3062f6af7551
> > Author: Keith Busch <keith.busch@...el.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.

It works for me on a XPS13 9360 too, only the 9380 is problematic.

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

I'll reply to Keith with that later.