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

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Date:   Thu, 10 Nov 2022 16:27:35 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     "Elliott, Robert (Servers)" <elliott@....com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...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" <rcu@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 1/2] rcu: Add RCU stall diagnosis information



On 2022/11/10 0:55, Elliott, Robert (Servers) wrote:
> 
> 
>> b/Documentation/admin-guide/kernel-parameters.txt
>> index a465d5242774af8..2729f3ad11d108b 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -5082,6 +5082,12 @@
>>  			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.
> 
> This description should start with:
>     "In kernels built with CONFIG_RCU_CPU_STALL_TIME=y, "
> 
> Also, that parameter name seems like it contains a time value, but
> it's really just treated as zero vs. anything else. Consider renaming
> it to rcu_cpu_stall_cputime_en or describing the values in the
> description ("0 disables, all other values enable").
> 
>> diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
>> +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 */
> 
> That should be "unsigned long" to match the other patch

We have discussed this before. And you mentioned:

irqs_sumstruct kernel_stat {
        unsigned long irqs_sum;
        unsigned int softirqs[NR_SOFTIRQS];
};

The softirqs field is an unsigned int, so the new function doesn't have
this inconsistency.

> 
> 
>> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
>> +static void print_cpu_stat_info(int cpu)
>> +{
> ...
>> +	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",
> 
> Those should all start with "\t" to match other related prints.

Right, thanks.

> 
> 
> .
> 

-- 
Regards,
  Zhen Lei