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 70017C43613 for ; Wed, 19 Jun 2019 20:52:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 373D42147A for ; Wed, 19 Jun 2019 20:52:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="isEfq6jw" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726379AbfFSUwP (ORCPT ); Wed, 19 Jun 2019 16:52:15 -0400 Received: from mail-qk1-f194.google.com ([209.85.222.194]:33038 "EHLO mail-qk1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726246AbfFSUwP (ORCPT ); Wed, 19 Jun 2019 16:52:15 -0400 Received: by mail-qk1-f194.google.com with SMTP id r6so495613qkc.0 for ; Wed, 19 Jun 2019 13:52:15 -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=z5rCzuSBrLaA6Op7MrdaVHZXcenmKCOz9zKA6giX+v0=; b=isEfq6jwPaqZYRufeqYVpJ4aUF6Eb6geHHhjFcA1KRzHKejvtKuLLqkcpIC5eGp9IL CL5KmPAcWju+EnTpWN3M64lTL/2QKtE/UZOmOn3pEn3cubJ+MUfD0QcGWyazytqFYmbZ d+H32Mpqyp8BdB9ZFBn9dRsK4qbKzYmySwFv/xBRxAHJ5vKUqA0NyC1t4FvA+HAY7l7K Rg5dLqeUzk2TFd+gkVR5XVmH9p/HijHY5ep7VD97WKpAUhk3ogXDCRdwCnC/1L6GZdgN +8hf6t60DlfUqIVIGTRQKBRLLHWG5b8KlCE5FFFv4WiAaViBYD5412kgCHPQz9X8vBOM Fmug== 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=z5rCzuSBrLaA6Op7MrdaVHZXcenmKCOz9zKA6giX+v0=; b=eNKEOosSdAy7PHv+eLMWfNtc5ra9nx6yMeIxsXNd5GP/VXVSJBjsg0Ha+KNk3ubUyP wNT9myq4Ph9d2fYkv52ZIBcipp/aX6Ol4O3Asr0yYnGJwfacwipzTjOC1DwoN76jJLGd 81kNjrolReldS5j1+2I6CdwZ9+Ch64rAg9b078wFIZcMsftEmHYob3vFs2PK07VUT2ya CrUTWYjMAsa4/Yn1QvlaQa/9BNh76TG+5R97sjlIFmlgBK0Uy0i4dK+pAaAK/CdgxgyS vyfqSS7u92Tn+/ISk6TdsvKzSE6mNqp6ClF5Er2sBTI13IELtSkpieT/Cf8CFDnlm0Oz FfOQ== X-Gm-Message-State: APjAAAUcByfzHn/lMXpzYkXwZ/1aTpWl8npU5RTQ+Kj9leSRu7cvkSCN fBzcxVtRtTrCD6LRH36nRzYw4PEmMtq0eUtFacopEQ== X-Google-Smtp-Source: APXvYqwkXi3xCG67StWJ97g9gbtDGdMv3fbCQX0ogpKxqIV6EucXjdPKsNGjHSyQ53Xs8SDPItZaYfdNbc5clFbMMoU= X-Received: by 2002:a05:620a:15b3:: with SMTP id f19mr37627773qkk.314.1560977534249; Wed, 19 Jun 2019 13:52:14 -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: From: Joel Fernandes Date: Wed, 19 Jun 2019 16:52:02 -0400 Message-ID: Subject: Re: Alternatives to /sys/kernel/debug/wakeup_sources To: Saravana Kannan Cc: Greg Kroah-Hartman , "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 4:41 PM 'Saravana Kannan' via kernel-team wrote: > > > On Wed, Jun 19, 2019, 11:55 AM 'Joel Fernandes' via kernel-team wrote: > > >> > > >> 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. > > > > > > > > > But this is not done in the UI thread context. So some thread running for more than 16ms shouldn't cause a frame drop. If it does, we have bigger problems. > > > > > > > Not really. That depends on the priority of the other thread and other > > things. It can obviously time share the same CPU as the UI thread if > > it is not configured correctly. Even with CFS it can reduce the time > > consumed by other "real-time" CFS threads. I am not sure what you are > > proposing, there are also (obviously) power issues with things running > > for long times pointlessly. We should try to do better if we can. As > > Greg said, some study/research can be done on the use case before > > settling for a solution (sysfs or other). > > > > Agree, power and optimization is good. Just saying that the UI example > is not a real one. If the UI thread is that poorly configured that > some thread running for a second can cause frame drops in a multicore > system, that's a problem with the UI framework design. We do know that historically there are problems with the UI thread's scheduling and folks are looking into DL scheduling for that. I was just giving UI thread as an example, there are also other low latency threads (audio etc). Anyway, I think we know the next steps here so we can park this discussion for now.