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

["Christophe Leroy (CS GROUP)" <chleroy@kernel.org>]

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 <sshegde@linux.ibm.com>

Reviewed-by: Christophe Leroy (CS GROUP) <chleroy@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) {