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[209.132.180.67]) by mx.google.com with ESMTP id a8si13909281ple.243.2019.06.18.14.23.09; Tue, 18 Jun 2019 14:23:24 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730445AbfFRVXF (ORCPT + 99 others); Tue, 18 Jun 2019 17:23:05 -0400 Received: from cloudserver094114.home.pl ([79.96.170.134]:41810 "EHLO cloudserver094114.home.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730102AbfFRVXE (ORCPT ); Tue, 18 Jun 2019 17:23:04 -0400 Received: from 79.184.254.20.ipv4.supernova.orange.pl (79.184.254.20) (HELO kreacher.localnet) by serwer1319399.home.pl (79.96.170.134) with SMTP (IdeaSmtpServer 0.83.267) id fbe5a615d4df22c3; Tue, 18 Jun 2019 23:23:01 +0200 From: "Rafael J. Wysocki" To: Sandeep Patil Cc: Tri Vo , viresh.kumar@linaro.org, Hridya Valsaraju , 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 Message-ID: <4587569.x9DSL43cXO@kreacher> In-Reply-To: <20190618182502.GC203031@google.com> References: <20190618182502.GC203031@google.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 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!