linux-kernel - Re: [PATCH v7 4/6] rcu: Add RCU stall diagnosis information

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Message-ID: <20221116223942.GA838972@lothringen>
Date:   Wed, 16 Nov 2022 23:39:42 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Zhen Lei <thunder.leizhen@...wei.com>
Cc:     "Paul E . McKenney" <paulmck@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org, Robert Elliott <elliott@....com>
Subject: Re: [PATCH v7 4/6] rcu: Add RCU stall diagnosis information

On Fri, Nov 11, 2022 at 09:07:07PM +0800, Zhen Lei wrote:
> @@ -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 */

This should be under #ifdef CONFIG_RCU_CPU_STALL_CPUTIME

> +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   ==> %lld(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),
> +		jiffies64_to_msecs(jiffies - rsrp->jiffies));

jiffies_to_msecs() should be enough.

Thanks.