linux-kernel - Re: [PATCH v5 1/4] PM: Add a sysfs file to represent time spent in hardware sleep state

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Message-ID: <CAJZ5v0iia9__-jWmawvsxninoTM5ZRtqhyUJme=noZMZJdUBrA@mail.gmail.com>
Date:   Fri, 31 Mar 2023 20:07:03 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     "Limonciello, Mario" <mario.limonciello@....com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Sven van Ashbrook <svenva@...omium.org>,
        John Stultz <jstultz@...gle.com>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Raul Rangel <rrangel@...omium.org>,
        David E Box <david.e.box@...el.com>,
        Rajat Jain <rajatja@...gle.com>,
        S-k Shyam-sundar <Shyam-sundar.S-k@....com>,
        Hans de Goede <hdegoede@...hat.com>,
        linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v5 1/4] PM: Add a sysfs file to represent time spent in
 hardware sleep state

On Fri, Mar 31, 2023 at 8:05 PM Limonciello, Mario
<mario.limonciello@....com> wrote:
>
> On 3/31/2023 13:01, Rafael J. Wysocki wrote:
> > On Thu, Mar 30, 2023 at 9:45 PM Mario Limonciello
> > <mario.limonciello@....com> wrote:
> >>
> >> Userspace can't easily discover how much of a sleep cycle was spent in a
> >> hardware sleep state without using kernel tracing and vendor specific sysfs
> >> or debugfs files.
> >>
> >> To make this information more discoverable, introduce a new sysfs file
> >> to represent the time spent in a sleep state.
> >
> > This is only in the most recent suspend-resume cycle, isn't it?
>
> Yes; that's correct.
>
> >
> > Wouldn't it be useful to have another attribute printing the
> > accumulated total HW sleep time?
> >
>
> I had considered this; but I didn't think it was actually very useful
> because userspace will get control at the end of every cycle and can
> accumulate those numbers if desirable.

Unless "user space" in question is actually a human, that is.