linux-kernel - Re: [PATCH v6 1/2] rcu: Add RCU stall diagnosis information

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Date:   Thu, 10 Nov 2022 14:55:13 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Frederic Weisbecker <frederic@...nel.org>
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 v6 1/2] rcu: Add RCU stall diagnosis information



On 2022/11/9 23:20, Frederic Weisbecker wrote:
> On Wed, Nov 09, 2022 at 05:37:37PM +0800, Zhen Lei wrote:
>> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
>> index ed93ddb8203d42c..e1ff23b2a14d71d 100644
>> --- a/kernel/rcu/tree.c
>> +++ b/kernel/rcu/tree.c
>> @@ -866,6 +866,23 @@ 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) {
>> +			u64 *cpustat;
>> +			struct rcu_snap_record *rsrp;
>> +
>> +			cpustat = kcpustat_cpu(rdp->cpu).cpustat;
>> +
>> +			rsrp = &rdp->snap_record;
>> +			rsrp->cputime_irq     = cpustat[CPUTIME_IRQ];
>> +			rsrp->cputime_softirq = cpustat[CPUTIME_SOFTIRQ];
>> +			rsrp->cputime_system  = cpustat[CPUTIME_SYSTEM];
> 
> You need to use kcpustat_field(), otherwise you'll get stalled values on nohz_full CPUs.

OK, I'll update it. Thanks.

> 
>> +			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_stall.h b/kernel/rcu/tree_stall.h
>> index 5653560573e22d6..7b6afb9c7b96dbe 100644
>> --- a/kernel/rcu/tree_stall.h
>> +++ b/kernel/rcu/tree_stall.h
>> @@ -428,6 +428,33 @@ 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;
>> +	struct rcu_snap_record *rsrp;
>> +	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
>> +
>> +	if (!rcu_cpu_stall_cputime)
>> +		return;
>> +
>> +	rsrp = &rdp->snap_record;
>> +	if (rsrp->gp_seq != rdp->gp_seq)
>> +		return;
>> +
>> +	cpustat = kcpustat_cpu(cpu).cpustat;
>> +
>> +	pr_err("         hardirqs   softirqs   csw/system\n");
>> +	pr_err(" 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("cputime: %8lld %10lld %12lld   ==> %lld(ms)\n",
>> +		div_u64(cpustat[CPUTIME_IRQ] - rsrp->cputime_irq, NSEC_PER_MSEC),
>> +		div_u64(cpustat[CPUTIME_SOFTIRQ] - rsrp->cputime_softirq, NSEC_PER_MSEC),
>> +		div_u64(cpustat[CPUTIME_SYSTEM] - rsrp->cputime_system,
>> NSEC_PER_MSEC),
> 
> Same here.

OK

> 
> Thanks.
> .
> 

-- 
Regards,
  Zhen Lei