Re: [patch V4 05/15] x86/irq: Suppress unlikely interrupt stats by default

Radu Rendec
2026-03-31T21:13:00Z

On Tue, 2026-03-31 at 09:25 +0200, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@kernel.org>
>
> Unlikely interrupt counters like the spurious vector and the synthetic APIC
> ICR read retry show up in /proc/interrupts with all counts 0 most of the
> time.
>
> As these are events which should never happen, suppress them by default and
> enable them for output when they actually happen.
>
> This requires a seperate bitmap as the description array is marked
> __ro_after_init. With that bitmap in place it becomes RO data.
>
> Signed-off-by: Thomas Gleixner <tglx@kernel.org>
> ---
> V4: Fix the bad idea of writing to __ro_after_init marked data
> V3: New patch
> ---
>  arch/x86/include/asm/hardirq.h |    1 +
>  arch/x86/kernel/apic/apic.c    |    2 +-
>  arch/x86/kernel/apic/ipi.c     |    2 +-
>  arch/x86/kernel/irq.c          |   28 ++++++++++++++++++----------
>  4 files changed, 21 insertions(+), 12 deletions(-)
> --- a/arch/x86/include/asm/hardirq.h
> +++ b/arch/x86/include/asm/hardirq.h
> @@ -68,6 +68,7 @@ DECLARE_PER_CPU_ALIGNED(struct pi_desc,
>  #define __ARCH_IRQ_STAT
>
>  #define inc_irq_stat(index) this_cpu_inc(irq_stat.counts[IRQ_COUNT_##index])
> +void irq_stat_inc_and_enable(enum irq_stat_counts which);

This is just a matter of style but for symmetry with inc_irq_stat(), I
would prepend '__' to the function name and create a wrapper macro that
adds the 'IRQ_COUNT_' prefix.

And for consistency (you also have inc_perf_irq_stat()) I would call it
inc_and_enable_irq_stat().

And yes, my comments above are totally bike shedding :)

>  #ifdef CONFIG_X86_LOCAL_APIC
>  #define inc_perf_irq_stat() inc_irq_stat(APIC_PERF)
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -2108,7 +2108,7 @@ static noinline void handle_spurious_int
>
>   trace_spurious_apic_entry(vector);
>
> - inc_irq_stat(SPURIOUS);
> + irq_stat_inc_and_enable(IRQ_COUNT_SPURIOUS);
>
>   /*
>   * If this is a spurious interrupt then do not acknowledge
> --- a/arch/x86/kernel/apic/ipi.c
> +++ b/arch/x86/kernel/apic/ipi.c
> @@ -120,7 +120,7 @@ u32 apic_mem_wait_icr_idle_timeout(void)
>   for (cnt = 0; cnt < 1000; cnt++) {
>   if (!(apic_read(APIC_ICR) & APIC_ICR_BUSY))
>   return 0;
> - inc_irq_stat(ICR_READ_RETRY);
> + irq_stat_inc_and_enable(IRQ_COUNT_ICR_READ_RETRY);
>   udelay(100);
>   }
>   return APIC_ICR_BUSY;
> --- a/arch/x86/kernel/irq.c
> +++ b/arch/x86/kernel/irq.c
> @@ -68,19 +68,24 @@ struct irq_stat_info {
>   const char *text;
>  };
>
> +#define DEFAULT_SUPPRESSED_VECTOR UINT_MAX
> +
>  #define ISS(idx, sym, txt) [IRQ_COUNT_##idx] = { .symbol = sym, .text = txt }
>
>  #define ITS(idx, sym, txt) [IRQ_COUNT_##idx] = \
>   { .skip_vector = idx## _VECTOR, .symbol = sym, .text = txt }
>
> -static struct irq_stat_info irq_stat_info[IRQ_COUNT_MAX] __ro_after_init = {
> +#define IDS(idx, sym, txt) [IRQ_COUNT_##idx] = \
> + { .skip_vector = DEFAULT_SUPPRESSED_VECTOR, .symbol = sym, .text = txt }
> +
> +static const struct irq_stat_info irq_stat_info[IRQ_COUNT_MAX] = {
>   ISS(NMI, "NMI", "  Non-maskable interrupts\n"),
>  #ifdef CONFIG_X86_LOCAL_APIC
>   ISS(APIC_TIMER, "LOC", "  Local timer interrupts\n"),
> - ISS(SPURIOUS, "SPU", "  Spurious interrupts\n"),
> + IDS(SPURIOUS, "SPU", "  Spurious interrupts\n"),
>   ISS(APIC_PERF, "PMI", "  Performance monitoring interrupts\n"),
>   ISS(IRQ_WORK, "IWI", "  IRQ work interrupts\n"),
> - ISS(ICR_READ_RETRY, "RTR", "  APIC ICR read retries\n"),
> + IDS(ICR_READ_RETRY, "RTR", "  APIC ICR read retries\n"),
>   ISS(X86_PLATFORM_IPI, "PLT", "  Platform interrupts\n"),
>  #endif
>  #ifdef CONFIG_SMP
> @@ -121,29 +126,32 @@ static struct irq_stat_info irq_stat_inf
>  #endif
>  };
>
> +static DECLARE_BITMAP(irq_stat_count_show, IRQ_COUNT_MAX) __read_mostly;
> +
>  static int __init irq_init_stats(void)
>  {
> - struct irq_stat_info *info = irq_stat_info;
> + const struct irq_stat_info *info = irq_stat_info;
>
>   for (unsigned int i = 0; i < ARRAY_SIZE(irq_stat_info); i++, info++) {
> - if (info->skip_vector && test_bit(info->skip_vector, system_vectors))
> - info->skip_vector = 0;
> + if (!info->skip_vector || (info->skip_vector != DEFAULT_SUPPRESSED_VECTOR &&
> +    test_bit(info->skip_vector, system_vectors)))
> + set_bit(i, irq_stat_count_show);
>   }
>
>  #ifdef CONFIG_X86_LOCAL_APIC
>   if (!x86_platform_ipi_callback)
> - irq_stat_info[IRQ_COUNT_X86_PLATFORM_IPI].skip_vector = 1;
> + clear_bit(IRQ_COUNT_X86_PLATFORM_IPI, irq_stat_count_show);
>  #endif
>
>  #ifdef CONFIG_X86_POSTED_MSI
>   if (!posted_msi_enabled())
> - irq_stat_info[IRQ_COUNT_POSTED_MSI_NOTIFICATION].skip_vector = 1;
> + clear_bit(IRQ_COUNT_POSTED_MSI_NOTIFICATION, irq_stat_count_show);
>  #endif
>
>  #ifdef CONFIG_X86_MCE_AMD
>   if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
>       boot_cpu_data.x86_vendor != X86_VENDOR_HYGON)
> - irq_stat_info[IRQ_COUNT_DEFERRED_VECTOR].skip_vector = 1;
> + clear_bit(IRQ_COUNT_DEFERRED_ERROR, irq_stat_count_show);
>  #endif
>   return 0;
>  }
> @@ -168,7 +176,7 @@ int arch_show_interrupts(struct seq_file
>   const struct irq_stat_info *info = irq_stat_info;
>
>   for (unsigned int i = 0; i < ARRAY_SIZE(irq_stat_info); i++, info++) {
> - if (info->skip_vector)
> + if (!test_bit(i, irq_stat_count_show))
>   continue;
>
>   seq_printf(p, "%*s:", prec, info->symbol);

Reviewed-by: Radu Rendec <radu@rendec.net>