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[209.132.180.67]) by mx.google.com with ESMTP id y34si10527448plb.186.2019.06.24.07.11.18; Mon, 24 Jun 2019 07:11:34 -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; dkim=pass header.i=@google.com header.s=20161025 header.b="izv8/ISA"; 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; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728547AbfFXM1e (ORCPT + 99 others); Mon, 24 Jun 2019 08:27:34 -0400 Received: from mail-qt1-f196.google.com ([209.85.160.196]:39361 "EHLO mail-qt1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728355AbfFXM1e (ORCPT ); Mon, 24 Jun 2019 08:27:34 -0400 Received: by mail-qt1-f196.google.com with SMTP id i34so14190501qta.6 for ; Mon, 24 Jun 2019 05:27:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=8pxgU2+2zAe7XjIsxn6dDw49AVrZSbjiR8p9fg9h61c=; b=izv8/ISAHD8c9UNVkM0cWQvNgJp3wRoXCluQG17yMRfV2pDdp1/uWG9IXPpDE/XYKH CQELaE70QgG60CSIem6+F6R2WvEQaZnzaFC1s3chbLxM9lxC2EBLHJWA9yMJ1J5AHz3P 7Zpy0MkZGWg/jnMkdoP+RjTjqsNzWfhxRh/xufz46CJ8Bi0bpWfwAGQ9z4+84AQcvFFV 7NSNuj1D+TU3msKRtqeLsf8HA47QG7I/FJcR/P/ZoG073n9/Vgaj78HN3O0I2bM28Q3P qcnLqv41V8hfaMJFwessbe/ky89XOtoWX4bZ9dD7wVAZ6zUgQjHis6jvi1iyT9uLt35P zlgA== 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=8pxgU2+2zAe7XjIsxn6dDw49AVrZSbjiR8p9fg9h61c=; b=rdXUMaWwcmz8KtRq5seeo+0weFShNED2Ys/twED2+GIYl8K/9D7GFSMVzuUnO4OtZa 4TGJXeTHVhDBIITNiKY95gRZqjgEr5nXu8eeKcGtTi+n+74XYfCOm7F/BulM2UeId1U1 4WcQkwGMzxWIBfr5+MJrLD3bSvO3tVUbnQiBpAhZ1PZenlVIok34RxPVEb4KdvnYpn0q QVPV0wcPQsW9gz40sDTh3vuVhTsKUxXHh4C1pDwtuA+N/zXFg+W34aSnFBr2V7X9FHik G5go0uiuPZrYJ7FkW2fwreHqJzKeN7F5P1ENYQYjkdRzjTWlw7yl8QmSioKQZxoDq97D G1DQ== X-Gm-Message-State: APjAAAXsnulDYc+5v6IHgAS+Eg7n6X9JjyhPJEvnjhAMDh22AyA559GH uMe81bDStXEy0wWSuyFdFqakzpo5UZq/ObvlPG0eBw== X-Received: by 2002:aed:21f0:: with SMTP id m45mr114648286qtc.391.1561379252759; Mon, 24 Jun 2019 05:27:32 -0700 (PDT) MIME-Version: 1.0 References: <20190618182502.GC203031@google.com> <4587569.x9DSL43cXO@kreacher> <20190624073659.GA13957@kroah.com> In-Reply-To: <20190624073659.GA13957@kroah.com> From: Joel Fernandes Date: Mon, 24 Jun 2019 08:27:21 -0400 Message-ID: Subject: Re: Alternatives to /sys/kernel/debug/wakeup_sources To: Greg Kroah-Hartman Cc: Tri Vo , "Rafael J. Wysocki" , "Rafael J. Wysocki" , Sandeep Patil , Viresh Kumar , Hridya Valsaraju , Linux PM , "Cc: Android Kernel" , 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 Mon, Jun 24, 2019 at 3:37 AM Greg Kroah-Hartman wrote: > > On Sun, Jun 23, 2019 at 06:48:43PM -0700, Tri Vo wrote: > > On Wed, Jun 19, 2019 at 1:35 AM Rafael J. Wysocki wrote: > > > > > > On Wed, Jun 19, 2019 at 1:52 AM Joel Fernandes wrote: > > > > > > > > On Tue, Jun 18, 2019 at 7:15 PM Tri Vo wrote: > > > > [snip] > > > > > > > > > > > > > > > > > > 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. > > > > > > > > Does that entail making each wake up source, a new sysfs node under a > > > > particular device, and then adding stats under that new node? > > > > > > Not under a device, because there are wakeup source objects without > > > associated devices. > > > > > > It is conceivable to have a "wakeup_sources" directory under > > > /sys/power/ and sysfs nodes for all wakeup sources in there. > > > > > > Then, instead of exposing wakeup statistics directly under > > > /sys/devices/.../power/, there can be symbolic links from there to the > > > new wakeup source nodes under "wakeup_sources" (so as to avoid > > > exposing the same data in two different places in sysfs, which may be > > > confusing). > > > > This may be a dumb question. Is it appropriate to make symbolic links > > in sysfs from one attribute to another attribute? For example, > > /sys/devices/.../power/wakeup_count -> > > /sys/power/wakeup_sources/.../wakeup_count. > > Why? would you want that? This sounds like what Rafael suggested (quoted above), right?