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=-8.3 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL autolearn=ham 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 C5E14C31E5B for ; Wed, 19 Jun 2019 18:55:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 97E27214AF for ; Wed, 19 Jun 2019 18:55:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="UBkEObav" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726322AbfFSSz3 (ORCPT ); Wed, 19 Jun 2019 14:55:29 -0400 Received: from mail-qt1-f174.google.com ([209.85.160.174]:41809 "EHLO mail-qt1-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726265AbfFSSz3 (ORCPT ); Wed, 19 Jun 2019 14:55:29 -0400 Received: by mail-qt1-f174.google.com with SMTP id d17so265291qtj.8 for ; Wed, 19 Jun 2019 11:55:28 -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=VB4BzkBmAfnn9smG4QdujxZEKSCe7ZFO081CDJvGHOs=; b=UBkEObavWJUPzYWqrX4PkO/rtS4osV2M2qFRIsoTfseYCV36DPH/UIBpKLZIMe2iw4 yNQQLyfbGIzSwMus48MynBPRVNPcq5dCS6HyB+CDOJPwpvfi1Q1AMnWVHx99ohYV2alN tsZNZPSNqb0A9uU9djzwqkjOO/ZX1genqYCUsk28nZWO5UmaF86MRtlsXO1f/zxwdU9S LX7J5xrcA2ORQBpqlIS4uKsxn8HXexnyDiNnnaG0/Ist0tZe72mJR/OmRkoFk8fANuMo /gkCW0eJyjkpMRDDXIRmiuIVryJoC0KOzlDg9KsXSj2DUsGBURY4X4haTbg9VF17+BvG dpcQ== 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=VB4BzkBmAfnn9smG4QdujxZEKSCe7ZFO081CDJvGHOs=; b=Sl3MS4cibYtWYd65C1FUVwxOd4JXYXxQ8n22OJy4ReaTKJOLG5p/F0AQ0HMiU3Id2/ K7B4RIllsQ1m2xByjiSKrLOq3lNZpXwJsxaN2ucJX7KuEpuYKUfg9y7RLKmsSowrKV0n +xGUyHCmTpPQr9DhOYHt3ZENhzdXsQAh0KIRoqi5E5opZOXnC1SvWBf6RVi6wGuRWfxU XzuF5m7d7qo4BBBs2vP6e+gi6XyB+wzpnftJidfzP4I7Mme4zXlf7V+Lk6983VgQze0K YoS1iUptTIVZCvGmAy+43gQoLERAg8koU+eZ0aMWjsax6PVuAlZox//BqvQdBJnWVGPH pfDg== X-Gm-Message-State: APjAAAXBvmvF+G0zRElYTrUz/b0e97OW5u4ZlCP40nqCewIz5lXLKDdt 1JUxPQ1eNDvPepYhaAn2mCd5vlrxbjhIqPiHqr4d/g== X-Google-Smtp-Source: APXvYqzI72YXA5i3v4S/pD3+OnXPb177CrNmWqsRGDJ8mXeyyj5HcEGb9STWniYmYDfsjLVQoaFs8+vVn+k77sHoPCY= X-Received: by 2002:aed:2389:: with SMTP id j9mr81727583qtc.244.1560970527825; Wed, 19 Jun 2019 11:55:27 -0700 (PDT) MIME-Version: 1.0 References: <20190618182502.GC203031@google.com> <4587569.x9DSL43cXO@kreacher> <20190619170750.GB10107@kroah.com> <20190619183523.GA7018@kroah.com> In-Reply-To: <20190619183523.GA7018@kroah.com> From: Joel Fernandes Date: Wed, 19 Jun 2019 14:55:16 -0400 Message-ID: Subject: Re: Alternatives to /sys/kernel/debug/wakeup_sources To: Greg Kroah-Hartman Cc: "Rafael J. Wysocki" , Tri Vo , "Rafael J. Wysocki" , Sandeep Patil , Viresh Kumar , Hridya Valsaraju , Linux PM , "Cc: Android Kernel" , LKML , Alexei Starovoitov , Steven Rostedt , Alexei Starovoitov Content-Type: text/plain; charset="UTF-8" Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On Wed, Jun 19, 2019 at 2:35 PM Greg Kroah-Hartman wrote: > > On Wed, Jun 19, 2019 at 02:01:36PM -0400, Joel Fernandes wrote: > > On Wed, Jun 19, 2019 at 1:07 PM Greg Kroah-Hartman > > wrote: > > > > > > On Wed, Jun 19, 2019 at 12:53:12PM -0400, Joel Fernandes wrote: > > > > > It is conceivable to have a "wakeup_sources" directory under > > > > > /sys/power/ and sysfs nodes for all wakeup sources in there. > > > > > > > > One of the "issues" with this is, now if you have say 100 wake up > > > > sources, with 10 entries each, then we're talking about a 1000 sysfs > > > > files. Each one has to be opened, and read individually. This adds > > > > overhead and it is more convenient to read from a single file. The > > > > problem is this single file is not ABI. So the question I guess is, > > > > how do we solve this in both an ABI friendly way while keeping the > > > > overhead low. > > > > > > How much overhead? Have you measured it, reading from virtual files is > > > fast :) > > > > I measured, and it is definitely not free. If you create and read a > > 1000 files and just return a string back, it can take up to 11-13 > > milliseconds (did not lock CPU frequencies, was just looking for > > average ball park). This is assuming that the counter reading is just > > doing that, and nothing else is being done to return the sysfs data > > which is probably not always true in practice. > > > > Our display pipeline deadline is around 16ms at 60Hz. Conceivably, any > > CPU scheduling competion reading sysfs can hurt the deadline. There's > > also the question of power - we definitely have spent time in the past > > optimizing other virtual files such as /proc/pid/smaps for this reason > > where it spent lots of CPU time. > > smaps was "odd", but that was done after measurements were actually made > to prove it was needed. That hasn't happened yet :) > > And is there a reason you have to do this every 16ms? Not every, I was just saying whenever it happens and a frame delivery deadline is missed, then a frame drop can occur which can result in a poor user experience.