Re: [patch v2 02/14] genirq/proc: Avoid formatting zero counts in /proc/interrupts

[Radu Rendec]

On Fri, 2026-03-20 at 14:21 +0100, Thomas Gleixner wrote:
> A large portion of interrupt count entries are zero. There is no point in
> formatting the zero value as it is way cheeper to just emit a constant
> string.
> 
> Collect the number of consecutive zero counts and emit them in one go
> before a non-zero count and at the end of the line.
> 
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxx>
> Reviewed-by: Dmitry Ilvokhin <d@xxxxxxxxxxxx>
> ---
> V2: Use sizeof() for ZSTR1_LEN - Dmitry
> ---
>  include/linux/interrupt.h |    1 +
>  kernel/irq/proc.c         |   42 +++++++++++++++++++++++++++++++++++++-----
>  2 files changed, 38 insertions(+), 5 deletions(-)
> 
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -864,6 +864,7 @@ static inline void init_irq_proc(void)
>  struct seq_file;
>  int show_interrupts(struct seq_file *p, void *v);
>  int arch_show_interrupts(struct seq_file *p, int prec);
> +void irq_proc_emit_counts(struct seq_file *p, unsigned int __percpu *cnts);
>  
>  extern int early_irq_init(void);
>  extern int arch_probe_nr_irqs(void);
> --- a/kernel/irq/proc.c
> +++ b/kernel/irq/proc.c
> @@ -450,6 +450,42 @@ int __weak arch_show_interrupts(struct s
>  # define ACTUAL_NR_IRQS irq_get_nr_irqs()
>  #endif
>  
> +#define ZSTR1 "          0"
> +#define ZSTR1_LEN	(sizeof(ZSTR1) - 1)
> +#define ZSTR16		ZSTR1 ZSTR1 ZSTR1 ZSTR1 ZSTR1 ZSTR1 ZSTR1 ZSTR1 \
> +			ZSTR1 ZSTR1 ZSTR1 ZSTR1 ZSTR1 ZSTR1 ZSTR1 ZSTR1
> +#define ZSTR256		ZSTR16 ZSTR16 ZSTR16 ZSTR16 ZSTR16 ZSTR16 ZSTR16 ZSTR16 \
> +			ZSTR16 ZSTR16 ZSTR16 ZSTR16 ZSTR16 ZSTR16 ZSTR16 ZSTR16
> +
> +static inline void irq_proc_emit_zero_counts(struct seq_file *p, unsigned int zeros)
> +{
> +	if (!zeros)
> +		return;
> +
> +	for (unsigned int n = min(zeros, 256); n; zeros -= n, n = min(zeros, 256))
> +		seq_write(p, ZSTR256, n * ZSTR1_LEN);
> +}
> +
> +static inline unsigned int irq_proc_emit_count(struct seq_file *p, unsigned int cnt,
> +					       unsigned int zeros)
> +{
> +	if (!cnt)
> +		return zeros + 1;
> +
> +	irq_proc_emit_zero_counts(p, zeros);
> +	seq_put_decimal_ull_width(p, " ", cnt, 10);
> +	return 0;
> +}
> +
> +void irq_proc_emit_counts(struct seq_file *p, unsigned int __percpu *cnts)
> +{
> +	unsigned int cpu, zeros = 0;
> +
> +	for_each_online_cpu(cpu)
> +		zeros = irq_proc_emit_count(p, per_cpu(*cnts, cpu), zeros);
> +	irq_proc_emit_zero_counts(p, zeros);
> +}
> +
>  int show_interrupts(struct seq_file *p, void *v)
>  {
>  	const unsigned int nr_irqs = irq_get_nr_irqs();
> @@ -485,11 +521,7 @@ int show_interrupts(struct seq_file *p,
>  		return 0;
>  
>  	seq_printf(p, "%*d:", prec, i);
> -	for_each_online_cpu(j) {
> -		unsigned int cnt = desc->kstat_irqs ? per_cpu(desc->kstat_irqs->cnt, j) : 0;
> -
> -		seq_put_decimal_ull_width(p, " ", cnt, 10);
> -	}
> +	irq_proc_emit_counts(p, &desc->kstat_irqs->cnt);
>  	seq_putc(p, ' ');
>  
>  	guard(raw_spinlock_irq)(&desc->lock);

Reviewed-by: Radu Rendec <radu@xxxxxxxxxx>