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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6EFDAC61DA4 for ; Wed, 22 Feb 2023 14:47:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231657AbjBVOrh (ORCPT ); Wed, 22 Feb 2023 09:47:37 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59486 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232169AbjBVOrZ (ORCPT ); Wed, 22 Feb 2023 09:47:25 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BF94E3BDAF for ; Wed, 22 Feb 2023 06:47:02 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 3544661464 for ; Wed, 22 Feb 2023 14:47:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 819ADC4339B; Wed, 22 Feb 2023 14:46:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1677077221; bh=Wy5hbT4ewIbxtuRGZo3BNmMi3nK/RbjQJn9sH1g4yFs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=FDmOTfUDDAvB318Tim6Svmwl4prd0CvCrO2yMhterj811AW25jGCizagfRmMU3PuO TtwrV6OOwv0mDAN5hY6twOv0xbamI50e31QG5hOBllfU0tfy1WiuNPI1PFNylJku9E QN4/p1q4Mkdo26fnClKlfGr9+zZk2dvpCo1jxbOYzQ+c677jHx0+V9SrSnUeintpfl JfyivG+S4iGlZNMP70TqKR+DSDUdc7Wbb+gTYayl3WGKBFkf2IXoLn4WuTbr4EivDM MdnybAwi2AGGOFmy382kl+pG1nF6aGuLLq2BGD/GXMWKOpgw5S3CvPPD7yfdLzqFb8 UabOOMYAYTN6w== From: Frederic Weisbecker To: Thomas Gleixner Cc: LKML , Frederic Weisbecker , Alexey Dobriyan , Wei Li , Peter Zijlstra , Mirsad Goran Todorovac , Yu Liao , Hillf Danton , Ingo Molnar Subject: [PATCH 2/8] timers/nohz: Only ever update sleeptime from idle exit Date: Wed, 22 Feb 2023 15:46:43 +0100 Message-Id: <20230222144649.624380-3-frederic@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230222144649.624380-1-frederic@kernel.org> References: <20230222144649.624380-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The idle and io sleeptime statistics appearing in /proc/stat can be currently updated from two sites: locally on idle exit and remotely by cpufreq. However there is no synchronization mechanism protecting concurrent updates. It is therefore possible to account the sleeptime twice, among all the possible broken scenarios. To prevent from breaking the sleeptime accounting source, restrict the sleeptime updates to the local idle exit site. If there is a delta to add since the last update, IO/Idle sleep time readers will now only compute the delta without actually writing it back to the internal idle statistic fields. This fixes a writer VS writer race. Note there are still two known reader VS writer races to handle. A subsequent patch will fix one. Reported-by: Yu Liao Acked-by: Peter Zijlstra (Intel) Cc: Hillf Danton Cc: Yu Liao Cc: Ingo Molnar Cc: Thomas Gleixner Cc: Wei Li Cc: Alexey Dobriyan Cc: Mirsad Goran Todorovac Signed-off-by: Frederic Weisbecker --- kernel/time/tick-sched.c | 103 ++++++++++++++++----------------------- 1 file changed, 41 insertions(+), 62 deletions(-) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index b0e3c9205946..9058b9eb8bc1 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -637,31 +637,21 @@ static void tick_nohz_update_jiffies(ktime_t now) touch_softlockup_watchdog_sched(); } -/* - * Updates the per-CPU time idle statistics counters - */ -static void -update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time) -{ - ktime_t delta; - - if (ts->idle_active) { - delta = ktime_sub(now, ts->idle_entrytime); - if (nr_iowait_cpu(cpu) > 0) - ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta); - else - ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); - ts->idle_entrytime = now; - } - - if (last_update_time) - *last_update_time = ktime_to_us(now); - -} - static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now) { - update_ts_time_stats(smp_processor_id(), ts, now, NULL); + ktime_t delta; + + if (WARN_ON_ONCE(!ts->idle_active)) + return; + + delta = ktime_sub(now, ts->idle_entrytime); + + if (nr_iowait_cpu(smp_processor_id()) > 0) + ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta); + else + ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); + + ts->idle_entrytime = now; ts->idle_active = 0; sched_clock_idle_wakeup_event(); @@ -674,6 +664,30 @@ static void tick_nohz_start_idle(struct tick_sched *ts) sched_clock_idle_sleep_event(); } +static u64 get_cpu_sleep_time_us(struct tick_sched *ts, ktime_t *sleeptime, + bool compute_delta, u64 *last_update_time) +{ + ktime_t now, idle; + + if (!tick_nohz_active) + return -1; + + now = ktime_get(); + if (last_update_time) + *last_update_time = ktime_to_us(now); + + if (ts->idle_active && compute_delta) { + ktime_t delta = ktime_sub(now, ts->idle_entrytime); + + idle = ktime_add(*sleeptime, delta); + } else { + idle = *sleeptime; + } + + return ktime_to_us(idle); + +} + /** * get_cpu_idle_time_us - get the total idle time of a CPU * @cpu: CPU number to query @@ -691,27 +705,9 @@ static void tick_nohz_start_idle(struct tick_sched *ts) u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time) { struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); - ktime_t now, idle; - - if (!tick_nohz_active) - return -1; - - now = ktime_get(); - if (last_update_time) { - update_ts_time_stats(cpu, ts, now, last_update_time); - idle = ts->idle_sleeptime; - } else { - if (ts->idle_active && !nr_iowait_cpu(cpu)) { - ktime_t delta = ktime_sub(now, ts->idle_entrytime); - - idle = ktime_add(ts->idle_sleeptime, delta); - } else { - idle = ts->idle_sleeptime; - } - } - - return ktime_to_us(idle); + return get_cpu_sleep_time_us(ts, &ts->idle_sleeptime, + !nr_iowait_cpu(cpu), last_update_time); } EXPORT_SYMBOL_GPL(get_cpu_idle_time_us); @@ -732,26 +728,9 @@ EXPORT_SYMBOL_GPL(get_cpu_idle_time_us); u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time) { struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); - ktime_t now, iowait; - if (!tick_nohz_active) - return -1; - - now = ktime_get(); - if (last_update_time) { - update_ts_time_stats(cpu, ts, now, last_update_time); - iowait = ts->iowait_sleeptime; - } else { - if (ts->idle_active && nr_iowait_cpu(cpu) > 0) { - ktime_t delta = ktime_sub(now, ts->idle_entrytime); - - iowait = ktime_add(ts->iowait_sleeptime, delta); - } else { - iowait = ts->iowait_sleeptime; - } - } - - return ktime_to_us(iowait); + return get_cpu_sleep_time_us(ts, &ts->iowait_sleeptime, + nr_iowait_cpu(cpu), last_update_time); } EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us); -- 2.34.1