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

Frederic Weisbecker
2022-11-09T15:20:31Z

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.

> + 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.

Thanks.