From patchwork Sat Nov 19 09:25:03 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Leizhen (ThunderTown)" X-Patchwork-Id: 13049661 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 759CDC433FE for ; Sat, 19 Nov 2022 09:26:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232812AbiKSJ0u (ORCPT ); Sat, 19 Nov 2022 04:26:50 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46784 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229515AbiKSJ0s (ORCPT ); Sat, 19 Nov 2022 04:26:48 -0500 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DC3E2776F2; Sat, 19 Nov 2022 01:26:47 -0800 (PST) Received: from dggpemm500023.china.huawei.com (unknown [172.30.72.54]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4NDp8v1PHczqSNy; Sat, 19 Nov 2022 17:22:55 +0800 (CST) Received: from dggpemm500006.china.huawei.com (7.185.36.236) by dggpemm500023.china.huawei.com (7.185.36.83) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Sat, 19 Nov 2022 17:26:46 +0800 Received: from thunder-town.china.huawei.com (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Sat, 19 Nov 2022 17:26:45 +0800 From: Zhen Lei To: "Paul E . McKenney" , Frederic Weisbecker , Neeraj Upadhyay , "Josh Triplett" , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , , CC: Zhen Lei , Robert Elliott Subject: [PATCH v8 1/6] genirq: Fix the return type of kstat_cpu_irqs_sum() Date: Sat, 19 Nov 2022 17:25:03 +0800 Message-ID: <20221119092508.1766-2-thunder.leizhen@huawei.com> X-Mailer: git-send-email 2.37.3.windows.1 In-Reply-To: <20221119092508.1766-1-thunder.leizhen@huawei.com> References: <20221119092508.1766-1-thunder.leizhen@huawei.com> MIME-Version: 1.0 X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org The type of member irqs_sum is unsigned long, so kstat_cpu_irqs_sum() should also return unsigned long. Otherwise, the value maybe truncated. Fixes: f2c66cd8eedd ("/proc/stat: scalability of irq num per cpu") Reported-by: Elliott, Robert (Servers) Signed-off-by: Zhen Lei --- include/linux/kernel_stat.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h index ddb5a358fd829f4..90e2fdc17d79ff8 100644 --- a/include/linux/kernel_stat.h +++ b/include/linux/kernel_stat.h @@ -75,7 +75,7 @@ extern unsigned int kstat_irqs_usr(unsigned int irq); /* * Number of interrupts per cpu, since bootup */ -static inline unsigned int kstat_cpu_irqs_sum(unsigned int cpu) +static inline unsigned long kstat_cpu_irqs_sum(unsigned int cpu) { return kstat_cpu(cpu).irqs_sum; } From patchwork Sat Nov 19 09:25:04 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Leizhen (ThunderTown)" X-Patchwork-Id: 13049663 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 6100EC43217 for ; Sat, 19 Nov 2022 09:26:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232804AbiKSJ0u (ORCPT ); Sat, 19 Nov 2022 04:26:50 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46804 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232036AbiKSJ0t (ORCPT ); Sat, 19 Nov 2022 04:26:49 -0500 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BF918776FE; Sat, 19 Nov 2022 01:26:48 -0800 (PST) Received: from dggpemm500024.china.huawei.com (unknown [172.30.72.53]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4NDpDt6t8GzRp9g; Sat, 19 Nov 2022 17:26:22 +0800 (CST) Received: from dggpemm500006.china.huawei.com (7.185.36.236) by dggpemm500024.china.huawei.com (7.185.36.203) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Sat, 19 Nov 2022 17:26:46 +0800 Received: from thunder-town.china.huawei.com (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Sat, 19 Nov 2022 17:26:46 +0800 From: Zhen Lei To: "Paul E . McKenney" , Frederic Weisbecker , Neeraj Upadhyay , "Josh Triplett" , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , , CC: Zhen Lei , Robert Elliott Subject: [PATCH v8 2/6] sched: Add helper kstat_cpu_softirqs_sum() Date: Sat, 19 Nov 2022 17:25:04 +0800 Message-ID: <20221119092508.1766-3-thunder.leizhen@huawei.com> X-Mailer: git-send-email 2.37.3.windows.1 In-Reply-To: <20221119092508.1766-1-thunder.leizhen@huawei.com> References: <20221119092508.1766-1-thunder.leizhen@huawei.com> MIME-Version: 1.0 X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org Similar to kstat_cpu_irqs_sum(), it counts the sum of all software interrupts on a specified CPU. Signed-off-by: Zhen Lei --- include/linux/kernel_stat.h | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h index 90e2fdc17d79ff8..898076e173a928a 100644 --- a/include/linux/kernel_stat.h +++ b/include/linux/kernel_stat.h @@ -67,6 +67,17 @@ static inline unsigned int kstat_softirqs_cpu(unsigned int irq, int cpu) return kstat_cpu(cpu).softirqs[irq]; } +static inline unsigned int kstat_cpu_softirqs_sum(int cpu) +{ + int i; + unsigned int sum = 0; + + for (i = 0; i < NR_SOFTIRQS; i++) + sum += kstat_softirqs_cpu(i, cpu); + + return sum; +} + /* * Number of interrupts per specific IRQ source, since bootup */ From patchwork Sat Nov 19 09:25:05 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Leizhen (ThunderTown)" X-Patchwork-Id: 13049664 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 823FFC4332F for ; Sat, 19 Nov 2022 09:27:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233420AbiKSJ0v (ORCPT ); Sat, 19 Nov 2022 04:26:51 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46810 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233351AbiKSJ0u (ORCPT ); Sat, 19 Nov 2022 04:26:50 -0500 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 57254776F1; Sat, 19 Nov 2022 01:26:49 -0800 (PST) Received: from dggpemm500021.china.huawei.com (unknown [172.30.72.53]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4NDpDv544NzRpBC; Sat, 19 Nov 2022 17:26:23 +0800 (CST) Received: from dggpemm500006.china.huawei.com (7.185.36.236) by dggpemm500021.china.huawei.com (7.185.36.109) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Sat, 19 Nov 2022 17:26:47 +0800 Received: from thunder-town.china.huawei.com (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Sat, 19 Nov 2022 17:26:47 +0800 From: Zhen Lei To: "Paul E . McKenney" , Frederic Weisbecker , Neeraj Upadhyay , "Josh Triplett" , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , , CC: Zhen Lei , Robert Elliott Subject: [PATCH v8 3/6] sched: Add helper nr_context_switches_cpu() Date: Sat, 19 Nov 2022 17:25:05 +0800 Message-ID: <20221119092508.1766-4-thunder.leizhen@huawei.com> X-Mailer: git-send-email 2.37.3.windows.1 In-Reply-To: <20221119092508.1766-1-thunder.leizhen@huawei.com> References: <20221119092508.1766-1-thunder.leizhen@huawei.com> MIME-Version: 1.0 X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org Returns the number of context switches on the specified CPU, which can be used to diagnose rcu stall. Signed-off-by: Zhen Lei --- include/linux/kernel_stat.h | 1 + kernel/sched/core.c | 5 +++++ 2 files changed, 6 insertions(+) diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h index 898076e173a928a..9935f7ecbfb9e31 100644 --- a/include/linux/kernel_stat.h +++ b/include/linux/kernel_stat.h @@ -52,6 +52,7 @@ DECLARE_PER_CPU(struct kernel_cpustat, kernel_cpustat); #define kstat_cpu(cpu) per_cpu(kstat, cpu) #define kcpustat_cpu(cpu) per_cpu(kernel_cpustat, cpu) +extern unsigned long long nr_context_switches_cpu(int cpu); extern unsigned long long nr_context_switches(void); extern unsigned int kstat_irqs_cpu(unsigned int irq, int cpu); diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 5800b0623ff3068..a0d19f67f2046d9 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5229,6 +5229,11 @@ bool single_task_running(void) } EXPORT_SYMBOL(single_task_running); +unsigned long long nr_context_switches_cpu(int cpu) +{ + return cpu_rq(cpu)->nr_switches; +} + unsigned long long nr_context_switches(void) { int i; From patchwork Sat Nov 19 09:25:06 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Leizhen (ThunderTown)" X-Patchwork-Id: 13049666 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 A348BC43219 for ; Sat, 19 Nov 2022 09:27:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233638AbiKSJ0x (ORCPT ); Sat, 19 Nov 2022 04:26:53 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46820 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233499AbiKSJ0v (ORCPT ); Sat, 19 Nov 2022 04:26:51 -0500 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1EAE5776F2; Sat, 19 Nov 2022 01:26:50 -0800 (PST) Received: from dggpemm500020.china.huawei.com (unknown [172.30.72.54]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4NDp9h4p2HzFqQx; Sat, 19 Nov 2022 17:23:36 +0800 (CST) Received: from dggpemm500006.china.huawei.com (7.185.36.236) by dggpemm500020.china.huawei.com (7.185.36.49) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Sat, 19 Nov 2022 17:26:48 +0800 Received: from thunder-town.china.huawei.com (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Sat, 19 Nov 2022 17:26:47 +0800 From: Zhen Lei To: "Paul E . McKenney" , Frederic Weisbecker , Neeraj Upadhyay , "Josh Triplett" , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , , CC: Zhen Lei , Robert Elliott Subject: [PATCH v8 4/6] rcu: Add RCU stall diagnosis information Date: Sat, 19 Nov 2022 17:25:06 +0800 Message-ID: <20221119092508.1766-5-thunder.leizhen@huawei.com> X-Mailer: git-send-email 2.37.3.windows.1 In-Reply-To: <20221119092508.1766-1-thunder.leizhen@huawei.com> References: <20221119092508.1766-1-thunder.leizhen@huawei.com> MIME-Version: 1.0 X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org Because RCU CPU stall warnings are driven from the scheduling-clock interrupt handler, a workload consisting of a very large number of short-duration hardware interrupts can result in misleading stall-warning messages. On systems supporting only a single level of interrupts, that is, where interrupts handlers cannot be interrupted, this can produce misleading diagnostics. The stack traces will show the innocent-bystander interrupted task, not the interrupts that are at the very least exacerbating the stall. This situation can be improved by displaying the number of interrupts and the CPU time that they have consumed. Diagnosing other types of stalls can be eased by also providing the count of softirqs and the CPU time that they consumed as well as the number of context switches and the task-level CPU time consumed. Consider the following output given this change: rcu: INFO: rcu_preempt self-detected stall on CPU rcu: 0-....: (1250 ticks this GP) rcu: hardirqs softirqs csw/system rcu: number: 624 45 0 rcu: cputime: 69 1 2425 ==> 2500(ms) This output shows that the number of hard and soft interrupts is small, there are no context switches, and the system takes up a lot of time. This indicates that the current task is looping with preemption disabled. The impact on system performance is negligible because snapshot is recorded only once for all continuous RCU stalls. This added debugging information is suppressed by default and can be enabled by building the kernel with CONFIG_RCU_CPU_STALL_CPUTIME=y or by booting with rcupdate.rcu_cpu_stall_cputime=1. Signed-off-by: Zhen Lei Reviewed-by: Mukesh Ojha Signed-off-by: Paul E. McKenney --- .../admin-guide/kernel-parameters.txt | 6 ++++ kernel/rcu/Kconfig.debug | 13 ++++++++ kernel/rcu/rcu.h | 1 + kernel/rcu/tree.c | 18 +++++++++++ kernel/rcu/tree.h | 19 ++++++++++++ kernel/rcu/tree_stall.h | 31 +++++++++++++++++++ kernel/rcu/update.c | 2 ++ 7 files changed, 90 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 811b2e6d4672685..ee7d9d962591c5d 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -5084,6 +5084,12 @@ rcupdate.rcu_cpu_stall_timeout to be used (after conversion from seconds to milliseconds). + rcupdate.rcu_cpu_stall_cputime= [KNL] + Provide statistics on the cputime and count of + interrupts and tasks during the sampling period. For + multiple continuous RCU stalls, all sampling periods + begin at half of the first RCU stall timeout. + rcupdate.rcu_expedited= [KNL] Use expedited grace-period primitives, for example, synchronize_rcu_expedited() instead diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug index 1b0c41d490f0588..ea654fdae9a06e0 100644 --- a/kernel/rcu/Kconfig.debug +++ b/kernel/rcu/Kconfig.debug @@ -95,6 +95,19 @@ config RCU_EXP_CPU_STALL_TIMEOUT says to use the RCU_CPU_STALL_TIMEOUT value converted from seconds to milliseconds. +config RCU_CPU_STALL_CPUTIME + bool "Provide additional RCU stall debug information" + depends on RCU_STALL_COMMON + default n + help + Collect statistics during the sampling period, such as the number of + (hard interrupts, soft interrupts, task switches) and the cputime of + (hard interrupts, soft interrupts, kernel tasks) are added to the + RCU stall report. For multiple continuous RCU stalls, all sampling + periods begin at half of the first RCU stall timeout. + The boot option rcupdate.rcu_cpu_stall_cputime has the same function + as this one, but will override this if it exists. + config RCU_TRACE bool "Enable tracing for RCU" depends on DEBUG_KERNEL diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index 65704cbc9df7b3d..70c79adfdc7046c 100644 --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -224,6 +224,7 @@ extern int rcu_cpu_stall_ftrace_dump; extern int rcu_cpu_stall_suppress; extern int rcu_cpu_stall_timeout; extern int rcu_exp_cpu_stall_timeout; +extern int rcu_cpu_stall_cputime; int rcu_jiffies_till_stall_check(void); int rcu_exp_jiffies_till_stall_check(void); diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 3ccad468887eb1a..219b4b516f3878f 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -866,6 +866,24 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) rdp->rcu_iw_gp_seq = rnp->gp_seq; irq_work_queue_on(&rdp->rcu_iw, rdp->cpu); } + + if (rcu_cpu_stall_cputime && rdp->snap_record.gp_seq != rdp->gp_seq) { + int cpu = rdp->cpu; + struct rcu_snap_record *rsrp; + struct kernel_cpustat *kcsp; + + kcsp = &kcpustat_cpu(cpu); + + rsrp = &rdp->snap_record; + rsrp->cputime_irq = kcpustat_field(kcsp, CPUTIME_IRQ, cpu); + rsrp->cputime_softirq = kcpustat_field(kcsp, CPUTIME_SOFTIRQ, cpu); + rsrp->cputime_system = kcpustat_field(kcsp, CPUTIME_SYSTEM, cpu); + rsrp->nr_hardirqs = kstat_cpu_irqs_sum(rdp->cpu); + rsrp->nr_softirqs = kstat_cpu_softirqs_sum(rdp->cpu); + rsrp->nr_csw = nr_context_switches_cpu(rdp->cpu); + rsrp->jiffies = jiffies; + rsrp->gp_seq = rdp->gp_seq; + } } return 0; diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index fcb5d696eb1700d..192536916f9a607 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -158,6 +158,23 @@ union rcu_noqs { u16 s; /* Set of bits, aggregate OR here. */ }; +/* + * Record the snapshot of the core stats at half of the first RCU stall timeout. + * The member gp_seq is used to ensure that all members are updated only once + * during the sampling period. The snapshot is taken only if this gp_seq is not + * equal to rdp->gp_seq. + */ +struct rcu_snap_record { + unsigned long gp_seq; /* Track rdp->gp_seq counter */ + u64 cputime_irq; /* Accumulated cputime of hard irqs */ + u64 cputime_softirq;/* Accumulated cputime of soft irqs */ + u64 cputime_system; /* Accumulated cputime of kernel tasks */ + unsigned long nr_hardirqs; /* Accumulated number of hard irqs */ + unsigned int nr_softirqs; /* Accumulated number of soft irqs */ + unsigned long long nr_csw; /* Accumulated number of task switches */ + unsigned long jiffies; /* Track jiffies value */ +}; + /* Per-CPU data for read-copy update. */ struct rcu_data { /* 1) quiescent-state and grace-period handling : */ @@ -262,6 +279,8 @@ struct rcu_data { short rcu_onl_gp_flags; /* ->gp_flags at last online. */ unsigned long last_fqs_resched; /* Time of last rcu_resched(). */ unsigned long last_sched_clock; /* Jiffies of last rcu_sched_clock_irq(). */ + struct rcu_snap_record snap_record; /* Snapshot of core stats at half of */ + /* the first RCU stall timeout */ long lazy_len; /* Length of buffered lazy callbacks. */ int cpu; diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 5653560573e22d6..6de15fb10bc4761 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -428,6 +428,35 @@ static bool rcu_is_rcuc_kthread_starving(struct rcu_data *rdp, unsigned long *jp return j > 2 * HZ; } +static void print_cpu_stat_info(int cpu) +{ + struct rcu_snap_record rsr, *rsrp; + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + struct kernel_cpustat *kcsp = &kcpustat_cpu(cpu); + + if (!rcu_cpu_stall_cputime) + return; + + rsrp = &rdp->snap_record; + if (rsrp->gp_seq != rdp->gp_seq) + return; + + rsr.cputime_irq = kcpustat_field(kcsp, CPUTIME_IRQ, cpu); + rsr.cputime_softirq = kcpustat_field(kcsp, CPUTIME_SOFTIRQ, cpu); + rsr.cputime_system = kcpustat_field(kcsp, CPUTIME_SYSTEM, cpu); + + pr_err("\t hardirqs softirqs csw/system\n"); + pr_err("\t number: %8ld %10d %12lld\n", + kstat_cpu_irqs_sum(cpu) - rsrp->nr_hardirqs, + kstat_cpu_softirqs_sum(cpu) - rsrp->nr_softirqs, + nr_context_switches_cpu(cpu) - rsrp->nr_csw); + pr_err("\tcputime: %8lld %10lld %12lld ==> %d(ms)\n", + div_u64(rsr.cputime_irq - rsrp->cputime_irq, NSEC_PER_MSEC), + div_u64(rsr.cputime_softirq - rsrp->cputime_softirq, NSEC_PER_MSEC), + div_u64(rsr.cputime_system - rsrp->cputime_system, NSEC_PER_MSEC), + jiffies_to_msecs(jiffies - rsrp->jiffies)); +} + /* * Print out diagnostic information for the specified stalled CPU. * @@ -484,6 +513,8 @@ static void print_cpu_stall_info(int cpu) data_race(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart, rcuc_starved ? buf : "", falsepositive ? " (false positive?)" : ""); + + print_cpu_stat_info(cpu); } /* Complain about starvation of grace-period kthread. */ diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index a05e23648c6b99f..76f9848a21cd5be 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -508,6 +508,8 @@ int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; module_param(rcu_cpu_stall_timeout, int, 0644); int rcu_exp_cpu_stall_timeout __read_mostly = CONFIG_RCU_EXP_CPU_STALL_TIMEOUT; module_param(rcu_exp_cpu_stall_timeout, int, 0644); +int rcu_cpu_stall_cputime __read_mostly = IS_ENABLED(CONFIG_RCU_CPU_STALL_CPUTIME); +module_param(rcu_cpu_stall_cputime, int, 0644); #endif /* #ifdef CONFIG_RCU_STALL_COMMON */ // Suppress boot-time RCU CPU stall warnings and rcutorture writer stall From patchwork Sat Nov 19 09:25:07 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Leizhen (ThunderTown)" X-Patchwork-Id: 13049665 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 6D46AC433FE for ; Sat, 19 Nov 2022 09:27:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233728AbiKSJ0y (ORCPT ); Sat, 19 Nov 2022 04:26:54 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46838 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233522AbiKSJ0w (ORCPT ); Sat, 19 Nov 2022 04:26:52 -0500 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0626A78195; Sat, 19 Nov 2022 01:26:51 -0800 (PST) Received: from dggpemm500022.china.huawei.com (unknown [172.30.72.55]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4NDpDm0DC4zHvlP; Sat, 19 Nov 2022 17:26:16 +0800 (CST) Received: from dggpemm500006.china.huawei.com (7.185.36.236) by dggpemm500022.china.huawei.com (7.185.36.162) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Sat, 19 Nov 2022 17:26:49 +0800 Received: from thunder-town.china.huawei.com (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Sat, 19 Nov 2022 17:26:48 +0800 From: Zhen Lei To: "Paul E . McKenney" , Frederic Weisbecker , Neeraj Upadhyay , "Josh Triplett" , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , , CC: Zhen Lei , Robert Elliott Subject: [PATCH v8 5/6] doc: Document CONFIG_RCU_CPU_STALL_CPUTIME=y stall information Date: Sat, 19 Nov 2022 17:25:07 +0800 Message-ID: <20221119092508.1766-6-thunder.leizhen@huawei.com> X-Mailer: git-send-email 2.37.3.windows.1 In-Reply-To: <20221119092508.1766-1-thunder.leizhen@huawei.com> References: <20221119092508.1766-1-thunder.leizhen@huawei.com> MIME-Version: 1.0 X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org This commit doucments how to quickly determine the bug causing a given RCU CPU stall fault warning based on the output information provided by CONFIG_RCU_CPU_STALL_CPUTIME=y. [ paulmck: Apply wordsmithing. ] Signed-off-by: Zhen Lei Signed-off-by: Paul E. McKenney --- Documentation/RCU/stallwarn.rst | 88 +++++++++++++++++++++++++++++++++ 1 file changed, 88 insertions(+) diff --git a/Documentation/RCU/stallwarn.rst b/Documentation/RCU/stallwarn.rst index dfa4db8c0931eaf..c1e92dfef40d501 100644 --- a/Documentation/RCU/stallwarn.rst +++ b/Documentation/RCU/stallwarn.rst @@ -390,3 +390,91 @@ for example, "P3421". It is entirely possible to see stall warnings from normal and from expedited grace periods at about the same time during the same run. + +RCU_CPU_STALL_CPUTIME +===================== + +In kernels built with CONFIG_RCU_CPU_STALL_CPUTIME=y or booted with +rcupdate.rcu_cpu_stall_cputime=1, the following additional information +is supplied with each RCU CPU stall warning:: + +rcu: hardirqs softirqs csw/system +rcu: number: 624 45 0 +rcu: cputime: 69 1 2425 ==> 2500(ms) + +These statistics are collected during the sampling period. The values +in row "number:" are the number of hard interrupts, number of soft +interrupts, and number of context switches on the stalled CPU. The +first three values in row "cputime:" indicate the CPU time in +milliseconds consumed by hard interrupts, soft interrupts, and tasks +on the stalled CPU. The last number is the measurement interval, again +in milliseconds. Because user-mode tasks normally do not cause RCU CPU +stalls, these tasks are typically kernel tasks, which is why only the +system CPU time are considered. + +The sampling period is shown as follows: +:<------------first timeout---------->:<-----second timeout----->: +:<--half timeout-->:<--half timeout-->: : +: :<--first period-->: : +: :<-----------second sampling period---------->: +: : : : +: snapshot time point 1st-stall 2nd-stall + + +The following describes four typical scenarios: + +1. A CPU looping with interrupts disabled.:: + + rcu: hardirqs softirqs csw/system + rcu: number: 0 0 0 + rcu: cputime: 0 0 0 ==> 2500(ms) + + Because interrupts have been disabled throughout the measurement + interval, there are no interrupts and no context switches. + Furthermore, because CPU time consumption was measured using interrupt + handlers, the system CPU consumption is misleadingly measured as zero. + This scenario will normally also have "(0 ticks this GP)" printed on + this CPU's summary line. + +2. A CPU looping with bottom halves disabled. + + This is similar to the previous example, but with non-zero number of + and CPU time consumed by hard interrupts, along with non-zero CPU + time consumed by in-kernel execution.:: + + rcu: hardirqs softirqs csw/system + rcu: number: 624 0 0 + rcu: cputime: 49 0 2446 ==> 2500(ms) + + The fact that there are zero softirqs gives a hint that these were + disabled, perhaps via local_bh_disable(). It is of course possible + that there were no softirqs, perhaps because all events that would + result in softirq execution are confined to other CPUs. In this case, + the diagnosis should continue as shown in the next example. + +3. A CPU looping with preemption disabled. + + Here, only the number of context switches is zero.:: + + rcu: hardirqs softirqs csw/system + rcu: number: 624 45 0 + rcu: cputime: 69 1 2425 ==> 2500(ms) + + This situation hints that the stalled CPU was looping with preemption + disabled. + +4. No looping, but massive hard and soft interrupts.:: + + rcu: hardirqs softirqs csw/system + rcu: number: xx xx 0 + rcu: cputime: xx xx 0 ==> 2500(ms) + + Here, the number and CPU time of hard interrupts are all non-zero, + but the number of context switches and the in-kernel CPU time consumed + are zero. The number and cputime of soft interrupts will usually be + non-zero, but could be zero, for example, if the CPU was spinning + within a single hard interrupt handler. + + If this type of RCU CPU stall warning can be reproduced, you can + narrow it down by looking at /proc/interrupts or by writing code to + trace each interrupt, for example, by referring to show_interrupts(). From patchwork Sat Nov 19 09:25:08 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Leizhen (ThunderTown)" X-Patchwork-Id: 13049667 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 9CA7AC4167E for ; Sat, 19 Nov 2022 09:27:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233765AbiKSJ0z (ORCPT ); Sat, 19 Nov 2022 04:26:55 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46840 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233543AbiKSJ0w (ORCPT ); Sat, 19 Nov 2022 04:26:52 -0500 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8AD9B781B5; Sat, 19 Nov 2022 01:26:51 -0800 (PST) Received: from dggpemm500023.china.huawei.com (unknown [172.30.72.53]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4NDp9k0rHfzFqQy; Sat, 19 Nov 2022 17:23:38 +0800 (CST) Received: from dggpemm500006.china.huawei.com (7.185.36.236) by dggpemm500023.china.huawei.com (7.185.36.83) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Sat, 19 Nov 2022 17:26:49 +0800 Received: from thunder-town.china.huawei.com (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Sat, 19 Nov 2022 17:26:49 +0800 From: Zhen Lei To: "Paul E . McKenney" , Frederic Weisbecker , Neeraj Upadhyay , "Josh Triplett" , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , , CC: Zhen Lei , Robert Elliott Subject: [PATCH v8 6/6] rcu: Align the output of RCU stall Date: Sat, 19 Nov 2022 17:25:08 +0800 Message-ID: <20221119092508.1766-7-thunder.leizhen@huawei.com> X-Mailer: git-send-email 2.37.3.windows.1 In-Reply-To: <20221119092508.1766-1-thunder.leizhen@huawei.com> References: <20221119092508.1766-1-thunder.leizhen@huawei.com> MIME-Version: 1.0 X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org The time stamps is added to the output when CONFIG_PRINTK_TIME=y, which will cause the alignment function to fail. So replace pr_cont() with pr_err(), which also decouples the printing of subfunctions. Before: [ 37.567343] rcu: INFO: rcu_preempt self-detected stall on CPU [ 37.567839] rcu: 0-....: (1500 ticks this GP) idle=*** [ 37.568270] (t=1501 jiffies g=4717 q=28 ncpus=4) [ 37.568668] CPU: 0 PID: 313 Comm: test0 Not tainted 6.1.0-rc4 #8 After: [ 36.762074] rcu: INFO: rcu_preempt self-detected stall on CPU [ 36.762543] rcu: 0-....: (1499 ticks this GP) idle=*** [ 36.763003] rcu: (t=1500 jiffies g=5097 q=27 ncpus=4) [ 36.763522] CPU: 0 PID: 313 Comm: test0 Not tainted 6.1.0-rc4 #9 Signed-off-by: Zhen Lei --- kernel/rcu/tree_stall.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 6de15fb10bc4761..f360894f5599d9d 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -619,7 +619,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) for_each_possible_cpu(cpu) totqlen += rcu_get_n_cbs_cpu(cpu); - pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu ncpus=%d)\n", + pr_err("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu ncpus=%d)\n", smp_processor_id(), (long)(jiffies - gps), (long)rcu_seq_current(&rcu_state.gp_seq), totqlen, rcu_state.n_online_cpus); if (ndetected) { @@ -680,7 +680,7 @@ static void print_cpu_stall(unsigned long gps) raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags); for_each_possible_cpu(cpu) totqlen += rcu_get_n_cbs_cpu(cpu); - pr_cont("\t(t=%lu jiffies g=%ld q=%lu ncpus=%d)\n", + pr_err("\t(t=%lu jiffies g=%ld q=%lu ncpus=%d)\n", jiffies - gps, (long)rcu_seq_current(&rcu_state.gp_seq), totqlen, rcu_state.n_online_cpus);