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Message-ID: <Z8h_Joy5zCuDpHbw@tardis>
Date: Wed, 5 Mar 2025 08:43:18 -0800
From: Boqun Feng <boqun.feng@...il.com>
To: Yongliang Gao <leonylgao@...il.com>
Cc: Neeraj.Upadhyay@....com, paulmck@...nel.org, frederic@...nel.org,
thunder.leizhen@...wei.com, frankjpliu@...cent.com,
kernelxing@...cent.com, rcu@...r.kernel.org,
linux-kernel@...r.kernel.org, Yongliang Gao <leonylgao@...cent.com>,
kernel test robot <lkp@...el.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v3] rcu/cpu_stall_cputime: fix the hardirq count for x86
architecture
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@...cent.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@...el.com>
> > Closes: https://lore.kernel.org/oe-kbuild-all/202501090842.SfI6QPGS-lkp@intel.com/
> > Signed-off-by: Yongliang Gao <leonylgao@...cent.com>
> > Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@....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()?
>
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@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
> >
> >
>
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