Re: [PATCH v3] rcu/cpu_stall_cputime: fix the hardirq count for x86 architecture

[Boqun Feng <boqun.feng@gmail.com>]

Hi Yongliang,

On Sun, Feb 16, 2025 at 04:41:09PM +0800, Yongliang Gao wrote:
> From: Yongliang Gao <leonylgao@tencent.com>
> 
> When counting the number of hardirqs in the x86 architecture,
> it is essential to add arch_irq_stat_cpu to ensure accuracy.
> 
> For example, a CPU loop within the rcu_read_lock function.
> 
> Before:
> [   70.910184] rcu: INFO: rcu_preempt self-detected stall on CPU
> [   70.910436] rcu:     3-....: (4999 ticks this GP) idle=***
> [   70.910711] rcu:              hardirqs   softirqs   csw/system
> [   70.910870] rcu:      number:        0        657            0
> [   70.911024] rcu:     cputime:        0          0         2498   ==> 2498(ms)
> [   70.911278] rcu:     (t=5001 jiffies g=3677 q=29 ncpus=8)
> 
> After:
> [   68.046132] rcu: INFO: rcu_preempt self-detected stall on CPU
> [   68.046354] rcu:     2-....: (4999 ticks this GP) idle=***
> [   68.046628] rcu:              hardirqs   softirqs   csw/system
> [   68.046793] rcu:      number:     2498        663            0
> [   68.046951] rcu:     cputime:        0          0         2496   ==> 2496(ms)
> [   68.047244] rcu:     (t=5000 jiffies g=3825 q=4 ncpus=8)
> 
> Fixes: be42f00b73a0 ("rcu: Add RCU stall diagnosis information")
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202501090842.SfI6QPGS-lkp@intel.com/
> Signed-off-by: Yongliang Gao <leonylgao@tencent.com>
> Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
> 

Thank you for the patch, I have one minor question to x86 maintainers
(Cced): does it make sense to fold the sum of arch_irq_stat_cpu() into
kstat_cpu_irqs_sum()?

Regards,
Boqun

> ---
> Changes from v2:
> - Add Reviewed-by 'Neeraj Upadhyay' information
> - Link to v2: https://lore.kernel.org/all/20250109024652.1342595-1-leonylgao@gmail.com
> Changes from v1:
> - Fix compilation error when using arm64-allnoconfig/riscv-randconfig. [kernel test robot]
> - Link to v1: https://lore.kernel.org/r/20250108065716.2888148-1-leonylgao%40gmail.com
> ---
> ---
>  kernel/rcu/tree.c       | 10 +++++++---
>  kernel/rcu/tree.h       |  2 +-
>  kernel/rcu/tree_stall.h |  4 ++--
>  3 files changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 475f31deed14..a0dab5923d03 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -781,6 +781,10 @@ static int rcu_watching_snap_save(struct rcu_data *rdp)
>  	return 0;
>  }
>  
> +#ifndef arch_irq_stat_cpu
> +#define arch_irq_stat_cpu(cpu) 0
> +#endif
> +
>  /*
>   * Returns positive if the specified CPU has passed through a quiescent state
>   * by virtue of being in or having passed through an dynticks idle state since
> @@ -916,9 +920,9 @@ static int rcu_watching_snap_recheck(struct rcu_data *rdp)
>  			rsrp->cputime_irq     = kcpustat_field(kcsp, CPUTIME_IRQ, cpu);
>  			rsrp->cputime_softirq = kcpustat_field(kcsp, CPUTIME_SOFTIRQ, cpu);
>  			rsrp->cputime_system  = kcpustat_field(kcsp, CPUTIME_SYSTEM, cpu);
> -			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->nr_hardirqs = kstat_cpu_irqs_sum(cpu) + arch_irq_stat_cpu(cpu);
> +			rsrp->nr_softirqs = kstat_cpu_softirqs_sum(cpu);
> +			rsrp->nr_csw = nr_context_switches_cpu(cpu);
>  			rsrp->jiffies = jiffies;
>  			rsrp->gp_seq = rdp->gp_seq;
>  		}
> diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
> index a9a811d9d7a3..1bba2225e744 100644
> --- a/kernel/rcu/tree.h
> +++ b/kernel/rcu/tree.h
> @@ -168,7 +168,7 @@ struct rcu_snap_record {
>  	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 */
> +	u64		nr_hardirqs;	/* Accumulated number of hard irqs */
>  	unsigned int	nr_softirqs;	/* Accumulated number of soft irqs */
>  	unsigned long long nr_csw;	/* Accumulated number of task switches */
>  	unsigned long   jiffies;	/* Track jiffies value */
> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> index 925fcdad5dea..56b21219442b 100644
> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -435,8 +435,8 @@ static void print_cpu_stat_info(int cpu)
>  	rsr.cputime_system  = kcpustat_field(kcsp, CPUTIME_SYSTEM, cpu);
>  
>  	pr_err("\t         hardirqs   softirqs   csw/system\n");
> -	pr_err("\t number: %8ld %10d %12lld\n",
> -		kstat_cpu_irqs_sum(cpu) - rsrp->nr_hardirqs,
> +	pr_err("\t number: %8lld %10d %12lld\n",
> +		kstat_cpu_irqs_sum(cpu) + arch_irq_stat_cpu(cpu) - rsrp->nr_hardirqs,
>  		kstat_cpu_softirqs_sum(cpu) - rsrp->nr_softirqs,
>  		nr_context_switches_cpu(cpu) - rsrp->nr_csw);
>  	pr_err("\tcputime: %8lld %10lld %12lld   ==> %d(ms)\n",
> -- 
> 2.39.3
> 
>