Re: [PATCH 2/3] powerpc/irq: Make irqstats array based

[Christophe Leroy (CS GROUP)]

Le 23/05/2026 à 19:40, Shrikanth Hegde a écrit :

Current irq_cpustat_t has separate member for handling each arch
specific interrupt type. The same can be achieved with array instead
indexed by corresponding irq counter type.

This helps to,

- Make it easy to integrate into genirq improvements by calling
   genirq provided irq_proc_emit_counts. That speeds up quite a bit
   by printing all 0's once as much as possible.

- Adding a new vector or software counter only requires to update the table
   and everything just works

- Remove ifdef usage a bit.

- Instead of going through each member, it simply becomes an array
   traversal.

Time taken to read /proc/interrupts 1000 times.
Base and v6 details can be found in cover-letter.
Base            :  103us
v6              :   63us
v6+this_patch   :   57us

A Decent 10% reduction can be seen in a system 240 CPUs. As the system
size increases the gain would be more as emitting 0 would reduce more
and more.

Signed-off-by: Shrikanth Hegde <sshe...@linux.ibm.com>

Reviewed-by: Christophe Leroy (CS GROUP) <chle...@kernel.org>

---
  arch/powerpc/include/asm/hardirq.h |  27 +++++---
  arch/powerpc/kernel/dbell.c        |   2 +-
  arch/powerpc/kernel/irq.c          | 107 ++++++++++-------------------
  arch/powerpc/kernel/time.c         |   6 +-
  arch/powerpc/kernel/traps.c        |  11 ++-
  arch/powerpc/kernel/watchdog.c     |   2 +-
  6 files changed, 64 insertions(+), 91 deletions(-)

diff --git a/arch/powerpc/include/asm/hardirq.h 
b/arch/powerpc/include/asm/hardirq.h
index bf3926a0c69c..38098e35b241 100644
--- a/arch/powerpc/include/asm/hardirq.h
+++ b/arch/powerpc/include/asm/hardirq.h
@@ -5,26 +5,33 @@
  #include <linux/threads.h>
  #include <linux/irq.h>

-typedef struct {

-       unsigned int timer_irqs_event;
-       unsigned int broadcast_irqs_event;
-       unsigned int timer_irqs_others;
-       unsigned int pmu_irqs;
-       unsigned int mce_exceptions;
-       unsigned int spurious_irqs;
-       unsigned int sreset_irqs;
+enum irq_stat_counts {
+       IRQ_COUNT_LOC_TIMER,
+       IRQ_COUNT_BCT_TIMER,
+       IRQ_COUNT_OTHER_TIMER,
+       IRQ_COUNT_SPURIOUS,
+       IRQ_COUNT_PMI,
+       IRQ_COUNT_MCE,
+       IRQ_COUNT_NMI_SRESET,
  #ifdef CONFIG_PPC_WATCHDOG
-       unsigned int soft_nmi_irqs;
+       IRQ_COUNT_WATCHDOG,
  #endif
  #ifdef CONFIG_PPC_DOORBELL
-       unsigned int doorbell_irqs;
+       IRQ_COUNT_DOORBELL,
  #endif
+       IRQ_COUNT_MAX,
+};
+
+typedef struct {
+       unsigned int counts[IRQ_COUNT_MAX];
  } ____cacheline_aligned irq_cpustat_t;

DECLARE_PER_CPU_SHARED_ALIGNED(irq_cpustat_t, irq_stat);

  DECLARE_PER_CPU(unsigned int, __softirq_pending);
  #define local_softirq_pending_ref       __softirq_pending

+#define inc_irq_stat(index) __this_cpu_inc(irq_stat.counts[IRQ_COUNT_##index])

+
  #define __ARCH_IRQ_STAT
  #define __ARCH_IRQ_EXIT_IRQS_DISABLED

diff --git a/arch/powerpc/kernel/dbell.c b/arch/powerpc/kernel/dbell.c

index 5712dd846263..f5e298a4c4c0 100644
--- a/arch/powerpc/kernel/dbell.c
+++ b/arch/powerpc/kernel/dbell.c
@@ -31,7 +31,7 @@ DEFINE_INTERRUPT_HANDLER_ASYNC(doorbell_exception)
                do_hard_irq_enable();

kvmppc_clear_host_ipi(smp_processor_id());

-       __this_cpu_inc(irq_stat.doorbell_irqs);
+       inc_irq_stat(DOORBELL);

smp_ipi_demux_relaxed(); /* already performed the barrier */ diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c

index f33df5e5c23f..e67a18f62142 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -84,79 +84,57 @@ u32 tau_interrupts(unsigned long cpu);
  #endif
  #endif /* CONFIG_PPC32 */

+struct irq_stat_info {

+       const char      *symbol;
+       const char      *text;
+};
+
+#define ISE(idx, sym, txt)[IRQ_COUNT_##idx] = { .symbol = sym, .text = txt}
+
+static struct irq_stat_info irq_stat_info[IRQ_COUNT_MAX] __ro_after_init = {
+       ISE(LOC_TIMER,          "LOC", "  Local timer interrupts for timer event 
device\n"),
+       ISE(BCT_TIMER,          "BCT", "  Broadcast timer interrupts for timer event 
device\n"),
+       ISE(OTHER_TIMER,        "LOC", "  Local timer interrupts for others\n"),
+       ISE(SPURIOUS,           "SPU", "  Spurious interrupts\n"),
+       ISE(PMI,                "PMI", "  Performance monitoring interrupts\n"),
+       ISE(MCE,                "MCE", "  Machine check exceptions\n"),
+       ISE(NMI_SRESET,         "NMI", "  System Reset interrupts\n"),
+#ifdef CONFIG_PPC_WATCHDOG
+       ISE(WATCHDOG,           "WDG", "  Watchdog soft-NMI interrupts\n"),
+#endif
+#ifdef CONFIG_PPC_DOORBELL
+       ISE(DOORBELL,           "DBL", "  Doorbell interrupts\n"),
+#endif
+};
+
  int arch_show_interrupts(struct seq_file *p, int prec)
  {
-       int j;
+       const struct irq_stat_info *info = irq_stat_info;
+
+       for (unsigned int i = 0; i < ARRAY_SIZE(irq_stat_info); i++, info++) {
+               seq_printf(p, "%*s:", prec, info->symbol);
+               irq_proc_emit_counts(p, &irq_stat.counts[i]);
+               seq_puts(p, info->text);
+       }

#if defined(CONFIG_PPC32) && defined(CONFIG_TAU_INT)

        if (tau_initialized) {
+               int j;
                seq_printf(p, "%*s:", prec, "TAU");
                for_each_online_cpu(j)
                        seq_put_decimal_ull_width(p, " ", tau_interrupts(j), 
10);
                seq_puts(p, "  PowerPC             Thermal Assist (cpu 
temp)\n");
        }
  #endif /* CONFIG_PPC32 && CONFIG_TAU_INT */
-
-       seq_printf(p, "%*s:", prec, "LOC");
-       for_each_online_cpu(j)
-               seq_put_decimal_ull_width(p, " ", per_cpu(irq_stat, 
j).timer_irqs_event, 10);
-        seq_printf(p, "  Local timer interrupts for timer event device\n");
-
-       seq_printf(p, "%*s:", prec, "BCT");
-       for_each_online_cpu(j)
-               seq_put_decimal_ull_width(p, " ", per_cpu(irq_stat, 
j).broadcast_irqs_event, 10);
-       seq_printf(p, "  Broadcast timer interrupts for timer event device\n");
-
-       seq_printf(p, "%*s:", prec, "LOC");
-       for_each_online_cpu(j)
-               seq_put_decimal_ull_width(p, " ", per_cpu(irq_stat, 
j).timer_irqs_others, 10);
-        seq_printf(p, "  Local timer interrupts for others\n");
-
-       seq_printf(p, "%*s:", prec, "SPU");
-       for_each_online_cpu(j)
-               seq_put_decimal_ull_width(p, " ", per_cpu(irq_stat, 
j).spurious_irqs, 10);
-       seq_printf(p, "  Spurious interrupts\n");
-
-       seq_printf(p, "%*s:", prec, "PMI");
-       for_each_online_cpu(j)
-               seq_put_decimal_ull_width(p, " ", per_cpu(irq_stat, 
j).pmu_irqs, 10);
-       seq_printf(p, "  Performance monitoring interrupts\n");
-
-       seq_printf(p, "%*s:", prec, "MCE");
-       for_each_online_cpu(j)
-               seq_put_decimal_ull_width(p, " ", per_cpu(irq_stat, 
j).mce_exceptions, 10);
-       seq_printf(p, "  Machine check exceptions\n");
-
  #ifdef CONFIG_PPC_BOOK3S_64
        if (cpu_has_feature(CPU_FTR_HVMODE)) {
+               int j;
                seq_printf(p, "%*s:", prec, "HMI");
                for_each_online_cpu(j)
                        seq_put_decimal_ull_width(p, " ", 
paca_ptrs[j]->hmi_irqs, 10);
                seq_printf(p, "  Hypervisor Maintenance Interrupts\n");
        }
  #endif
-
-       seq_printf(p, "%*s:", prec, "NMI");
-       for_each_online_cpu(j)
-               seq_put_decimal_ull_width(p, " ", per_cpu(irq_stat, 
j).sreset_irqs, 10);
-       seq_printf(p, "  System Reset interrupts\n");
-
-#ifdef CONFIG_PPC_WATCHDOG
-       seq_printf(p, "%*s:", prec, "WDG");
-       for_each_online_cpu(j)
-               seq_put_decimal_ull_width(p, " ", per_cpu(irq_stat, 
j).soft_nmi_irqs, 10);
-       seq_printf(p, "  Watchdog soft-NMI interrupts\n");
-#endif
-
-#ifdef CONFIG_PPC_DOORBELL
-       if (cpu_has_feature(CPU_FTR_DBELL)) {
-               seq_printf(p, "%*s:", prec, "DBL");
-               for_each_online_cpu(j)
-                       seq_put_decimal_ull_width(p, " ", per_cpu(irq_stat, 
j).doorbell_irqs, 10);
-               seq_printf(p, "  Doorbell interrupts\n");
-       }
-#endif
-
        return 0;
  }

@@ -165,24 +143,15 @@ int arch_show_interrupts(struct seq_file *p, int prec)

   */
  u64 arch_irq_stat_cpu(unsigned int cpu)
  {
-       u64 sum = per_cpu(irq_stat, cpu).timer_irqs_event;
+       irq_cpustat_t *p = per_cpu_ptr(&irq_stat, cpu);
+       u64 sum = 0;
+
+       for (unsigned int i = 0; i < ARRAY_SIZE(irq_stat_info); i++)
+               sum += p->counts[i];

- sum += per_cpu(irq_stat, cpu).broadcast_irqs_event;

-       sum += per_cpu(irq_stat, cpu).pmu_irqs;
-       sum += per_cpu(irq_stat, cpu).mce_exceptions;
-       sum += per_cpu(irq_stat, cpu).spurious_irqs;
-       sum += per_cpu(irq_stat, cpu).timer_irqs_others;
  #ifdef CONFIG_PPC_BOOK3S_64
        sum += paca_ptrs[cpu]->hmi_irqs;
  #endif
-       sum += per_cpu(irq_stat, cpu).sreset_irqs;
-#ifdef CONFIG_PPC_WATCHDOG
-       sum += per_cpu(irq_stat, cpu).soft_nmi_irqs;
-#endif
-#ifdef CONFIG_PPC_DOORBELL
-       sum += per_cpu(irq_stat, cpu).doorbell_irqs;
-#endif
-
        return sum;
  }

@@ -248,7 +217,7 @@ static void __do_irq(struct pt_regs *regs, unsigned long oldsp) /* And finally process it */

        if (unlikely(!irq))
-               __this_cpu_inc(irq_stat.spurious_irqs);
+               inc_irq_stat(SPURIOUS);
        else
                generic_handle_irq(irq);

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c

index 4bbeb8644d3d..44da7be36199 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -572,13 +572,13 @@ DEFINE_INTERRUPT_HANDLER_ASYNC(timer_interrupt)
        now = get_tb();
        if (now >= *next_tb) {
                evt->event_handler(evt);
-               __this_cpu_inc(irq_stat.timer_irqs_event);
+               inc_irq_stat(LOC_TIMER);
        } else {
                now = *next_tb - now;
                if (now > decrementer_max)
                        now = decrementer_max;
                set_dec_or_work(now);
-               __this_cpu_inc(irq_stat.timer_irqs_others);
+               inc_irq_stat(OTHER_TIMER);
        }

trace_timer_interrupt_exit(regs);

@@ -591,7 +591,7 @@ EXPORT_SYMBOL(timer_interrupt);
  void timer_broadcast_interrupt(void)
  {
        tick_receive_broadcast();
-       __this_cpu_inc(irq_stat.broadcast_irqs_event);
+       inc_irq_stat(BCT_TIMER);
  }
  #endif

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c

index cb8e9357383e..a8f15154bd9a 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -459,8 +459,7 @@ DEFINE_INTERRUPT_HANDLER_NMI(system_reset_exception)
        }

hv_nmi_check_nonrecoverable(regs);

-
-       __this_cpu_inc(irq_stat.sreset_irqs);
+       inc_irq_stat(NMI_SRESET);

/* See if any machine dependent calls */

        if (ppc_md.system_reset_exception) {
@@ -817,7 +816,7 @@ static void __machine_check_exception(struct pt_regs *regs)
  {
        int recover = 0;

- __this_cpu_inc(irq_stat.mce_exceptions);

+       inc_irq_stat(MCE);

add_taint(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE); @@ -1932,8 +1931,7 @@ DEFINE_INTERRUPT_HANDLER(vsx_unavailable_tm)

  DECLARE_INTERRUPT_HANDLER_NMI(performance_monitor_exception_nmi);
  DEFINE_INTERRUPT_HANDLER_NMI(performance_monitor_exception_nmi)
  {
-       __this_cpu_inc(irq_stat.pmu_irqs);
-
+       inc_irq_stat(PMI);
        perf_irq(regs);

return 0;

@@ -1943,8 +1941,7 @@ 
DEFINE_INTERRUPT_HANDLER_NMI(performance_monitor_exception_nmi)
  DECLARE_INTERRUPT_HANDLER_ASYNC(performance_monitor_exception_async);
  DEFINE_INTERRUPT_HANDLER_ASYNC(performance_monitor_exception_async)
  {
-       __this_cpu_inc(irq_stat.pmu_irqs);
-
+       inc_irq_stat(PMI);
        perf_irq(regs);
  }

diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c

index 764001deb060..f516eeccc9f6 100644
--- a/arch/powerpc/kernel/watchdog.c
+++ b/arch/powerpc/kernel/watchdog.c
@@ -381,7 +381,7 @@ DEFINE_INTERRUPT_HANDLER_NMI(soft_nmi_interrupt)
        if (!cpumask_test_cpu(cpu, &wd_cpus_enabled))
                return 0;

- __this_cpu_inc(irq_stat.soft_nmi_irqs);

+       inc_irq_stat(WATCHDOG);

tb = get_tb();

        if (tb - per_cpu(wd_timer_tb, cpu) >= wd_panic_timeout_tb) {