* [PATCH v2 2/3] powerpc/irq: Make irqstats array based
2026-05-29 12:40 [PATCH v2 0/3] powerpc/irq: Use optimizations for /proc/interrupts Shrikanth Hegde
2026-05-29 12:40 ` [PATCH v2 1/3] powerpc/irq: Move __softirq_pending out of irq_stat Shrikanth Hegde
@ 2026-05-29 12:40 ` Shrikanth Hegde
2026-05-29 12:40 ` [PATCH v2 3/3] powerpc/irq: Suppress unlikely interrupt stats by default Shrikanth Hegde
2 siblings, 0 replies; 4+ messages in thread
From: Shrikanth Hegde @ 2026-05-29 12:40 UTC (permalink / raw)
To: christophe.leroy, maddy, linuxppc-dev, tglx
Cc: sshegde, linux-kernel, Christophe Leroy (CS GROUP)
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.
Reviewed-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
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 b4472288e0d4..5794adc2e8df 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -574,13 +574,13 @@ 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);
@@ -593,7 +593,7 @@ 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) {
--
2.47.3
^ permalink raw reply related [flat|nested] 4+ messages in thread* [PATCH v2 3/3] powerpc/irq: Suppress unlikely interrupt stats by default
2026-05-29 12:40 [PATCH v2 0/3] powerpc/irq: Use optimizations for /proc/interrupts Shrikanth Hegde
2026-05-29 12:40 ` [PATCH v2 1/3] powerpc/irq: Move __softirq_pending out of irq_stat Shrikanth Hegde
2026-05-29 12:40 ` [PATCH v2 2/3] powerpc/irq: Make irqstats array based Shrikanth Hegde
@ 2026-05-29 12:40 ` Shrikanth Hegde
2 siblings, 0 replies; 4+ messages in thread
From: Shrikanth Hegde @ 2026-05-29 12:40 UTC (permalink / raw)
To: christophe.leroy, maddy, linuxppc-dev, tglx; +Cc: sshegde, linux-kernel
Some interrupts are always zero and that is expected since they occur
very rarely and are mostly error indications. Don't print them by
default.
"MCE" - "Machine check exceptions"
"NMI" - "System Reset interrupts"
Print them if they occur once. Maintain a bitmap to know which
interrupts are to be printed.
Time taken to read /proc/interrupts 1000 times.
Base and v6 details can be found in cover-letter.
Base : 103us
v6 : 63us
v6+patch 1+2 : 57us
v6+patch 1+2+3 : 54us
Patch 3 shows an additional 5% gain compared to patch 1+2. So it does
make sense to print them only if they are ever set.
Note: Since /proc/interrupts depend on kconfig and arch dependent,
userspace tools don't make explicit assumptions.
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
arch/powerpc/include/asm/hardirq.h | 1 +
arch/powerpc/kernel/irq.c | 37 +++++++++++++++++++++++++++---
arch/powerpc/kernel/traps.c | 4 ++--
3 files changed, 37 insertions(+), 5 deletions(-)
diff --git a/arch/powerpc/include/asm/hardirq.h b/arch/powerpc/include/asm/hardirq.h
index 38098e35b241..be6cd5aab016 100644
--- a/arch/powerpc/include/asm/hardirq.h
+++ b/arch/powerpc/include/asm/hardirq.h
@@ -31,6 +31,7 @@ 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])
+void inc_irq_stat_and_enable(enum irq_stat_counts which);
#define __ARCH_IRQ_STAT
#define __ARCH_IRQ_EXIT_IRQS_DISABLED
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index e67a18f62142..0a6a0e707fe8 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -87,9 +87,13 @@ u32 tau_interrupts(unsigned long cpu);
struct irq_stat_info {
const char *symbol;
const char *text;
+ int optional;
};
-#define ISE(idx, sym, txt)[IRQ_COUNT_##idx] = { .symbol = sym, .text = txt}
+/* ISE - IRQ STAT ENABLED, ISC - IRQ STAT CONDITIONAL */
+#define ISE(idx, sym, txt)[IRQ_COUNT_##idx] = { .symbol = sym, .text = txt, .optional = 0}
+#define ISC(idx, sym, txt)[IRQ_COUNT_##idx] = { .symbol = sym, .text = txt, .optional = 1}
+
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"),
@@ -97,8 +101,8 @@ static struct irq_stat_info irq_stat_info[IRQ_COUNT_MAX] __ro_after_init = {
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"),
+ ISC(MCE, "MCE", " Machine check exceptions\n"),
+ ISC(NMI_SRESET, "NMI", " System Reset interrupts\n"),
#ifdef CONFIG_PPC_WATCHDOG
ISE(WATCHDOG, "WDG", " Watchdog soft-NMI interrupts\n"),
#endif
@@ -107,11 +111,25 @@ static struct irq_stat_info irq_stat_info[IRQ_COUNT_MAX] __ro_after_init = {
#endif
};
+/*
+ * Used for default disabled counters to increment the stats and to enable the
+ * entry for /proc/interrupts output.
+ */
+static DECLARE_BITMAP(irq_stat_count_show, IRQ_COUNT_MAX) __read_mostly;
+void inc_irq_stat_and_enable(enum irq_stat_counts which)
+{
+ __this_cpu_inc(irq_stat.counts[which]);
+ set_bit(which, irq_stat_count_show);
+}
+
int arch_show_interrupts(struct seq_file *p, int prec)
{
const struct irq_stat_info *info = irq_stat_info;
for (unsigned int i = 0; i < ARRAY_SIZE(irq_stat_info); i++, info++) {
+ if (info->optional && !test_bit(i, irq_stat_count_show))
+ continue;
+
seq_printf(p, "%*s:", prec, info->symbol);
irq_proc_emit_counts(p, &irq_stat.counts[i]);
seq_puts(p, info->text);
@@ -138,6 +156,19 @@ int arch_show_interrupts(struct seq_file *p, int prec)
return 0;
}
+static int __init irq_init_stats(void)
+{
+ struct irq_stat_info *info = irq_stat_info;
+
+ for (unsigned int i = 0; i < ARRAY_SIZE(irq_stat_info); i++, info++) {
+ if (info->optional == 0)
+ set_bit(i, irq_stat_count_show);
+ }
+
+ return 0;
+}
+late_initcall(irq_init_stats);
+
/*
* /proc/stat helpers
*/
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index a8f15154bd9a..3eacbd20fc80 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -459,7 +459,7 @@ DEFINE_INTERRUPT_HANDLER_NMI(system_reset_exception)
}
hv_nmi_check_nonrecoverable(regs);
- inc_irq_stat(NMI_SRESET);
+ inc_irq_stat_and_enable(IRQ_COUNT_NMI_SRESET);
/* See if any machine dependent calls */
if (ppc_md.system_reset_exception) {
@@ -816,7 +816,7 @@ static void __machine_check_exception(struct pt_regs *regs)
{
int recover = 0;
- inc_irq_stat(MCE);
+ inc_irq_stat_and_enable(IRQ_COUNT_MCE);
add_taint(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE);
--
2.47.3
^ permalink raw reply related [flat|nested] 4+ messages in thread