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

Thomas Gleixner
2026-03-31T07:25:54Z

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);

#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);