From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Sandeep Patil <sspatil@android.com>
Cc: Tri Vo <trong@android.com>,
viresh.kumar@linaro.org, Hridya Valsaraju <hridya@google.com>,
linux-pm@vger.kernel.org, kernel-team@android.com,
gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org
Subject: Re: Alternatives to /sys/kernel/debug/wakeup_sources
Date: Tue, 18 Jun 2019 23:23:00 +0200 [thread overview]
Message-ID: <4587569.x9DSL43cXO@kreacher> (raw)
In-Reply-To: <20190618182502.GC203031@google.com>
On Tuesday, June 18, 2019 10:17:16 PM CEST Sandeep Patil wrote:
>
> Hi Rafael, Viresh etc.
>
> On Tue, Jun 11, 2019 at 10:31:16AM -0700, Tri Vo wrote:
> > On Tue, Jun 4, 2019 at 5:23 PM Tri Vo <trong@android.com> wrote:
> > >
> > > Hello Rafael,
> > >
> > > Currently, Android reads wakeup sources statistics from
> > > /sys/kernel/debug/wakeup_sources in production environment. This
> > > information is used, for example, to report which wake lock prevents
> > > the device from suspending.
>
> Android's usage of the 'wakeup_sources' from debugfs can is linked at[1].
> Basically, android's battery stats implementation to plot history for suspend
> blocking wakeup sources over device's boot cycle. This is used both for power
> specific bug reporting but also is one of the stats that will be used towards
> attributing the battery consumption to specific processes over the period of
> time.
>
> Android depended on the out-of-tree /proc/wakelocks before and now relies on
> wakeup_sources debugfs entry heavily for the aforementioned use cases.
>
> > >
> > > Android userspace reading wakeup_sources is not ideal because:
> > > - Debugfs API is not stable, i.e. Android tools built on top of it are
> > > not guaranteed to be backward/forward compatible.
> > > - This file requires debugfs to be mounted, which itself is
> > > undesirable for security reasons.
> > >
> > > To address these problems, we want to contribute a way to expose these
> > > statistics that doesn't depend on debugfs.
> > >
> > > Some initial thoughts/questions: Should we expose the stats in sysfs?
> > > Or maybe implement eBPF-based solution? What do you think?
>
> We are going through Android's out-of-tree kernel dependencies along with
> userspace APIs that are not necessarily considered "stable and forever
> supported" upstream. The debugfs dependencies showed up on our radar as a
> result and so we are wondering if we should worry about changes in debugfs
> interface and hence the question(s) below.
>
> So, can we rely on /d/wakeup_sources to be considered a userspace API and
> hence maintained stable as we do for other /proc and /sys entries?
>
> If yes, then we will go ahead and add tests for this in LTP or
> somewhere else suitable.
No, debugfs is not ABI.
> If no, then we would love to hear suggestions for any changes that need to be
> made or we simply just move the debugfs entry into somewhere like
> /sys/power/ ?
No, moving that entire file from debugfs into sysfs is not an option either.
The statistics for the wakeup sources associated with devices are already there
under /sys/devices/.../power/ , but I guess you want all wakeup sources?
That would require adding a kobject to struct wakeup_source and exposing
all of the statistics as separate attributes under it. In which case it would be
good to replace the existing wakeup statistics under /sys/devices/.../power/
with symbolic links to the attributes under the wakeup_source kobject.
> As a side effect, if the entry moves out of debugfs, Android can run without
> mounting debugfs in production that I assume is a good thing.
And really Android developers might have thought about this a bit earlier.
Thanks!
next prev parent reply other threads:[~2019-06-18 21:23 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CANA+-vCThdRivg7nrMK5QoFu8SGUzEVSvSyp0H2CPyy9==Tqog@mail.gmail.com>
[not found] ` <CANA+-vARQ9Ao=W1oEArrAQ0sqh757orq=-=kytdVPhstm-3E9w@mail.gmail.com>
2019-06-18 20:17 ` Alternatives to /sys/kernel/debug/wakeup_sources Sandeep Patil
2019-06-18 21:23 ` Rafael J. Wysocki [this message]
2019-06-18 23:15 ` Tri Vo
2019-06-18 23:52 ` Joel Fernandes
2019-06-19 8:35 ` Rafael J. Wysocki
2019-06-19 10:33 ` Joel Fernandes
2019-06-19 16:51 ` Sandeep Patil
2019-06-19 16:53 ` Joel Fernandes
2019-06-19 17:07 ` Greg Kroah-Hartman
2019-06-19 18:01 ` Joel Fernandes
2019-06-19 18:31 ` Tri Vo
2019-06-19 18:35 ` Greg Kroah-Hartman
2019-06-19 18:55 ` Joel Fernandes
[not found] ` <CAGETcx-ZZRc_jtBws2cFTe1wjiWeBowdqfqOhcCJV_7AUyBEVw@mail.gmail.com>
2019-06-19 20:09 ` Joel Fernandes
2019-06-19 20:40 ` Saravana Kannan
2019-06-19 20:52 ` Joel Fernandes
2019-06-24 1:48 ` Tri Vo
2019-06-24 7:36 ` Greg Kroah-Hartman
2019-06-24 12:27 ` Joel Fernandes
2019-06-24 21:55 ` Rafael J. Wysocki
2019-06-24 22:14 ` Tri Vo
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