From patchwork Mon Apr 25 01:07:45 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Rafael J. Wysocki" X-Patchwork-Id: 8922431 X-Patchwork-Delegate: rjw@sisk.pl Return-Path: X-Original-To: patchwork-linux-pm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 885F89F372 for ; Mon, 25 Apr 2016 01:04:52 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 8ADDC20125 for ; Mon, 25 Apr 2016 01:04:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 62A0C20122 for ; Mon, 25 Apr 2016 01:04:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752523AbcDYBEt (ORCPT ); Sun, 24 Apr 2016 21:04:49 -0400 Received: from cloudserver094114.home.net.pl ([79.96.170.134]:45674 "HELO cloudserver094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752369AbcDYBEs (ORCPT ); Sun, 24 Apr 2016 21:04:48 -0400 Received: from 217.96.254.83.ipv4.supernova.orange.pl (217.96.254.83) (HELO vostro.rjw.lan) by serwer1319399.home.pl (79.96.170.134) with SMTP (IdeaSmtpServer v0.80.2) id a11e6b8d7563957f; Mon, 25 Apr 2016 03:04:45 +0200 From: "Rafael J. Wysocki" To: Linux PM list Cc: Linux Kernel Mailing List , Viresh Kumar , Chen Yu Subject: [PATCH] cpufreq: governor: Fix prev_load initialization in cpufreq_governor_start() Date: Mon, 25 Apr 2016 03:07:45 +0200 Message-ID: <5284094.6jVZZT3rEB@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/4.5.0-rc1+; KDE/4.11.5; x86_64; ; ) MIME-Version: 1.0 Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org X-Spam-Status: No, score=-7.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Rafael J. Wysocki The way cpufreq_governor_start() initializes j_cdbs->prev_load is questionable. First off, j_cdbs->prev_cpu_wall used as a denominator in the computation may be zero. The case this happens is when get_cpu_idle_time_us() returns -1 and get_cpu_idle_time_jiffy() used to return that number is called exactly at the jiffies_64 wrap time. It is rather hard to trigger that error, but it is not impossible and it will just crash the kernel then. Second, j_cdbs->prev_load is computed as the average load during the entire time since the system started and it may not reflect the load in the previous sampling period (as it is expected to). That doesn't play well with the way dbs_update() uses that value. Namely, if the update time delta (wall_time) happens do be greater than twice the sampling rate on the first invocation of it, the initial value of j_cdbs->prev_load (which may be completely off) will be returned to the caller as the current load (unless it is equal to zero and unless another CPU sharing the same policy object has a greater load value). For this reason, notice that the prev_load field of struct cpu_dbs_info is only used by dbs_update() and only in that one place, so if cpufreq_governor_start() is modified to always initialize it to 0, it will make dbs_update() always compute the actual load first time it checks the update time delta against the doubled sampling rate (after initialization) and there won't be any side effects of it. Consequently, modify cpufreq_governor_start() as described. Signed-off-by: Rafael J. Wysocki Acked-by: Viresh Kumar --- drivers/cpufreq/cpufreq_governor.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Index: linux-pm/drivers/cpufreq/cpufreq_governor.c =================================================================== --- linux-pm.orig/drivers/cpufreq/cpufreq_governor.c +++ linux-pm/drivers/cpufreq/cpufreq_governor.c @@ -508,12 +508,12 @@ static int cpufreq_governor_start(struct for_each_cpu(j, policy->cpus) { struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j); - unsigned int prev_load; j_cdbs->prev_cpu_idle = get_cpu_idle_time(j, &j_cdbs->prev_cpu_wall, io_busy); - - prev_load = j_cdbs->prev_cpu_wall - j_cdbs->prev_cpu_idle; - j_cdbs->prev_load = 100 * prev_load / (unsigned int)j_cdbs->prev_cpu_wall; + /* + * Make the first invocation of dbs_update() compute the load. + */ + j_cdbs->prev_load = 0; if (ignore_nice) j_cdbs->prev_cpu_nice = kcpustat_cpu(j).cpustat[CPUTIME_NICE];