From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 96AC5C31E5D for ; Tue, 18 Jun 2019 23:15:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 603EB20873 for ; Tue, 18 Jun 2019 23:15:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=android.com header.i=@android.com header.b="RFEpZtIn" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729246AbfFRXP1 (ORCPT ); Tue, 18 Jun 2019 19:15:27 -0400 Received: from mail-ot1-f67.google.com ([209.85.210.67]:39448 "EHLO mail-ot1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726091AbfFRXP0 (ORCPT ); Tue, 18 Jun 2019 19:15:26 -0400 Received: by mail-ot1-f67.google.com with SMTP id r21so14381517otq.6 for ; Tue, 18 Jun 2019 16:15:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=android.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=CIsSf2GXvyDDqSHsag5yZpphi9br2QVejLk/bHmvVOU=; b=RFEpZtInek3Io86FQLQYPSGxY5DbPdOrWHexhniqE/836Q7GoKyLBn5C/t/u+NyiOm k91tU09m/SUR6H+dxUwX47Mx4GxGk1hO2WU7XCGEQgxBh6DQSwf6heoiugn9iNCP6o5F z0oWkzGRcr+eDW8VjYY3lDtJld2zAiNrHmEkRMTX8rm2qA96nYlH41u3teob2jmMXlYF t5acmoJ55ZKaiOWycmMm5ZqMgAzS36wBkDzLqNjJ6qe7bdv0/tAUs+OZeZdiAEyKUSx+ IoTYLES+7UrlT3ovI04C3hEM6/FCT+4dMoRFCP6QvEZZjdDVg+h4Mmak/08Vnz1J24dL PuuQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=CIsSf2GXvyDDqSHsag5yZpphi9br2QVejLk/bHmvVOU=; b=rjAd67wLNbw5Xt2gMgCejy318BtnwH8hoz0W/LExccytypHgwoWymtMFuIaYgmrH8l ApKzRG8qj8iHhqvSsGJPAlaGMK2WNgGWGi5xtBHVxMi6iD0VHOHhK7tUDsF/zpt3b3Z3 40cJsYevHL5mEQD6LY/aPguitmVj2tTy/sZIKS6SDz5+SfENL87NFvzch1ZtPEuKfPkF V/OOYsUwKs86P7FYWebcclAbM8EpOUy6EMHkq5kQXDPMaJmvSkbEOP/wlWZNN4QjdCNE cX7goF8PmA2M07AN1Gejy+b+f7yesiY8bUve4ar76P16zafv9X/DP+9RIQbVwOUlLU2O MBOw== X-Gm-Message-State: APjAAAWBFUFJofwSH/ID1myUa3+7i22WjfInKCYcfAgLPI0rHHPZIx+N Ibxpy0JPCQSOmakvdZ6w7IBgD/URPHnXne+YmyEFyw== X-Google-Smtp-Source: APXvYqwNQLjWPtV+R8pF+k88qhC8khbqFVOtcNqlqN3daCyPXfL1Az/KXqmwaSLH86Onsw0+GoRPuR0JCs8tLaQzTqk= X-Received: by 2002:a9d:5911:: with SMTP id t17mr17885454oth.159.1560899725814; Tue, 18 Jun 2019 16:15:25 -0700 (PDT) MIME-Version: 1.0 References: <20190618182502.GC203031@google.com> <4587569.x9DSL43cXO@kreacher> In-Reply-To: <4587569.x9DSL43cXO@kreacher> From: Tri Vo Date: Tue, 18 Jun 2019 16:15:14 -0700 Message-ID: Subject: Re: Alternatives to /sys/kernel/debug/wakeup_sources To: "Rafael J. Wysocki" Cc: Sandeep Patil , Viresh Kumar , Hridya Valsaraju , linux-pm@vger.kernel.org, kernel-team@android.com, gregkh@linuxfoundation.org, LKML Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 18, 2019 at 2:23 PM Rafael J. Wysocki 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 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!