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 DCAD9C43613 for ; Wed, 19 Jun 2019 20:41:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A80402080C for ; Wed, 19 Jun 2019 20:41:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="c0ZMTdca" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726246AbfFSUlQ (ORCPT ); Wed, 19 Jun 2019 16:41:16 -0400 Received: from mail-ot1-f68.google.com ([209.85.210.68]:44668 "EHLO mail-ot1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726175AbfFSUlP (ORCPT ); Wed, 19 Jun 2019 16:41:15 -0400 Received: by mail-ot1-f68.google.com with SMTP id b7so388467otl.11 for ; Wed, 19 Jun 2019 13:41:15 -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=mpUwpi6ZiT7FkXDLHkwFe14AauTrVYWRjFSVpnxhQLU=; b=c0ZMTdcaJyks4wdvB1Rq6tA62+E/+cF9RAhLcN8ezYFiuZO0A1AhbhNzo3aUy8/mxZ dArKgmGkPzr7O2lBUDil6B3eBsM0BB4dK4DGNZmH/LzTRzkB90DRkHm3j5AtUJdlXx2d ZZQ11DcrVCVbxpalH09fZ5FXcHGLu1fKuLNeRYN+gnsBxq+QSw7dagXluvH/eYjNqZBr DFJ66MjwcJz68EvR6cX9N9qOqdvi7c5p6mnDbdbH4shTgfhrquK868NVivke/+xGUjf4 +msp8t2w1TcfLgAsw5P50Fqq7LK3m6YcFfGcy51AWI5rZPILzqY78BCzmClq9Pvd8/D6 ec1A== 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=mpUwpi6ZiT7FkXDLHkwFe14AauTrVYWRjFSVpnxhQLU=; b=Lw+XI8pbwpAJsDQN6W321N1Tct9Euc9nthyi+Hwk3RdtW/ogGCdXxX9gSRqPVK3Fdk ZrtXl4hjoHnn6ZIxWENpHiFoJkkN8PNQq4x/ZUWnet7XsIDG8RDwfmeeZxHvmTV7EiWd RA+SXGjX85/o0eRiVG5qIxe971mdkN0DhIFpY5zH6ez6LwoPeP3d/2/GJkOCREBBKnBD brPWowAYsjWgRkDOfFkTek9XSTJfj5DTXdhRMvOYIhAZJcHakIpBrEIiDNwXIM4xY0bl 0ivvHnkhkg5lldCg0XW4Of6tGyXBhlXRrNiJ+Uw1umoP1wXUNP7pkAx8TZMRCfpsuVd6 NKXA== X-Gm-Message-State: APjAAAVE6jYtPDQ92vyzU8adqcidVZfSkwwHbcrdvXo1T8k37Fj9B0Zk PiMIrcIheIrkyLQBwpMYDy3YlZi8c7L8JEHGDEE1Nw== X-Google-Smtp-Source: APXvYqzc1Dd4mob2T+s748nFLXyfVx+1T/mxSLN1akN+bwaEyK8Ck6yOMYt6tEnCE//WRs66k+/EcydYCR0SJstxyAw= X-Received: by 2002:a9d:1909:: with SMTP id j9mr5350706ota.139.1560976874737; Wed, 19 Jun 2019 13:41:14 -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: Saravana Kannan Date: Wed, 19 Jun 2019 13:40:38 -0700 Message-ID: Subject: Re: Alternatives to /sys/kernel/debug/wakeup_sources To: Joel Fernandes 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 1:09 PM 'Joel Fernandes' via kernel-team wrote: > > On Wed, Jun 19, 2019 at 3:59 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. -Saravana > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. >