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

[Boqun Feng]

On Sun, Feb 16, 2025 at 06:29:54PM -0800, Boqun Feng wrote:
> Hi Yongliang,
> 
> On Sun, Feb 16, 2025 at 04:41:09PM +0800, Yongliang Gao wrote:
> > From: Yongliang Gao <leonylgao@xxxxxxxxxxx>
> > 
> > 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@xxxxxxxxx>
> > Closes: https://lore.kernel.org/oe-kbuild-all/202501090842.SfI6QPGS-lkp@xxxxxxxxx/
> > Signed-off-by: Yongliang Gao <leonylgao@xxxxxxxxxxx>
> > Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@xxxxxxx>
> > 
> 
> 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()?
> 

Queued for further tests and reviews, but my question for x86
maintainers remains ;-)

Regards,
Boqun

> Regards,
> Boqun
> 
> > ---
> > Changes from v2:
> > - Add Reviewed-by 'Neeraj Upadhyay' information
> > - Link to v2: https://lore.kernel.org/all/20250109024652.1342595-1-leonylgao@xxxxxxxxx
> > 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
> > 
> > 
>