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

Elliott, Robert (Servers)
2022-11-09T17:00:19Z

> 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.