From patchwork Sat Oct 22 12:45:25 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Leizhen (ThunderTown)" X-Patchwork-Id: 13015960 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 928A8C433FE for ; Sat, 22 Oct 2022 12:46:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229683AbiJVMqN (ORCPT ); Sat, 22 Oct 2022 08:46:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60218 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229766AbiJVMqL (ORCPT ); Sat, 22 Oct 2022 08:46:11 -0400 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 215B1FAA55; Sat, 22 Oct 2022 05:46:09 -0700 (PDT) Received: from dggpemm500022.china.huawei.com (unknown [172.30.72.55]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4Mvgtm0YkTz15LxN; Sat, 22 Oct 2022 20:41:20 +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, 22 Oct 2022 20:46:07 +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, 22 Oct 2022 20:46:07 +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 Subject: [PATCH v2 3/3] rcu: Add RCU stall diagnosis information Date: Sat, 22 Oct 2022 20:45:25 +0800 Message-ID: <20221022124525.2080-4-thunder.leizhen@huawei.com> X-Mailer: git-send-email 2.37.3.windows.1 In-Reply-To: <20221022124525.2080-1-thunder.leizhen@huawei.com> References: <20221022124525.2080-1-thunder.leizhen@huawei.com> MIME-Version: 1.0 X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org In some extreme cases, such as the I/O pressure test, the CPU usage may be 100%, causing RCU stall. In this case, the printed information about current is not useful. Displays the number and usage of hard interrupts, soft interrupts, and context switches that are generated within half of the CPU stall timeout, can help us make a general judgment. In other cases, we can preliminarily determine whether an infinite loop occurs when local_irq, local_bh or preempt is disabled. For example: 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) The example above shows that the number of hard and soft interrupts is small, there is zero context switching, and the system takes up a lot of time. We can quickly conclude that the current task is infinitely looped with preempt_disable(). The impact on system performance is negligible because snapshot is recorded only one time after 1/2 CPU stall timeout. Signed-off-by: Zhen Lei --- kernel/rcu/tree.c | 16 ++++++++++++++++ kernel/rcu/tree.h | 11 +++++++++++ kernel/rcu/tree_stall.h | 28 ++++++++++++++++++++++++++++ 3 files changed, 55 insertions(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 6bb8e72bc8151ef..56c49a3117e7a81 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -931,6 +931,22 @@ 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 (rdp->snap_record.gp_seq != rdp->gp_seq) { + u64 *cpustat; + struct rcu_snap_record *r; + + cpustat = kcpustat_cpu(rdp->cpu).cpustat; + + r = &rdp->snap_record; + r->cputime_irq = cpustat[CPUTIME_IRQ]; + r->cputime_softirq = cpustat[CPUTIME_SOFTIRQ]; + r->cputime_system = cpustat[CPUTIME_SYSTEM]; + r->nr_hardirqs = kstat_cpu_irqs_sum(rdp->cpu); + r->nr_softirqs = kstat_cpu_softirqs_sum(rdp->cpu); + r->nr_csw = nr_context_switches_cpu(rdp->cpu); + r->gp_seq = rdp->gp_seq; + } } return 0; diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index d4a97e40ea9c3e2..fb3121d15cca6f8 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -158,6 +158,16 @@ union rcu_noqs { u16 s; /* Set of bits, aggregate OR here. */ }; +struct rcu_snap_record { + unsigned long gp_seq; + u64 cputime_irq; + u64 cputime_softirq; + u64 cputime_system; + unsigned int nr_hardirqs; + unsigned int nr_softirqs; + unsigned long long nr_csw; +}; + /* Per-CPU data for read-copy update. */ struct rcu_data { /* 1) quiescent-state and grace-period handling : */ @@ -262,6 +272,7 @@ 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; int cpu; }; diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 5653560573e22d6..f8c9d0284d116a8 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -428,6 +428,32 @@ 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) +{ + u64 *cpustat; + unsigned long half_timeout; + struct rcu_snap_record *r; + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + + r = &rdp->snap_record; + if (r->gp_seq != rdp->gp_seq) + return; + + cpustat = kcpustat_cpu(cpu).cpustat; + half_timeout = rcu_jiffies_till_stall_check() / 2; + + pr_err(" hardirqs softirqs csw/system\n"); + pr_err(" number: %8d %10d %12lld\n", + kstat_cpu_irqs_sum(cpu) - r->nr_hardirqs, + kstat_cpu_softirqs_sum(cpu) - r->nr_softirqs, + nr_context_switches_cpu(cpu) - r->nr_csw); + pr_err("cputime: %8lld %10lld %12lld ==> %lld(ms)\n", + div_u64(cpustat[CPUTIME_IRQ] - r->cputime_irq, NSEC_PER_MSEC), + div_u64(cpustat[CPUTIME_SOFTIRQ] - r->cputime_softirq, NSEC_PER_MSEC), + div_u64(cpustat[CPUTIME_SYSTEM] - r->cputime_system, NSEC_PER_MSEC), + jiffies64_to_msecs(half_timeout)); +} + /* * Print out diagnostic information for the specified stalled CPU. * @@ -484,6 +510,8 @@ 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. */