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

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Message-ID: <MW5PR84MB18423CA291ABCD3DCCE3D416AB3E9@MW5PR84MB1842.NAMPRD84.PROD.OUTLOOK.COM>
Date:   Wed, 9 Nov 2022 16:55:45 +0000
From:   "Elliott, Robert (Servers)" <elliott@....com>
To:     Zhen Lei <thunder.leizhen@...wei.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



> 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


> 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.