On Tue, Jun 18, 2019 at 2:23 PM Rafael J. Wysocki <r...@rjwysocki.net> wrote: > > 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 <tr...@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.
Thanks for your input, Rafael! Your suggestion makes sense. I'll work on a patch for this. > > > 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. I'm still learning about kernel development. And Android has made missteps before. So I figured it's a good idea to ask first :) Thanks!