Commit f2c66cd8 authored by KAMEZAWA Hiroyuki's avatar KAMEZAWA Hiroyuki Committed by Linus Torvalds

/proc/stat: scalability of irq num per cpu

/proc/stat shows the total number of all interrupts to each cpu.  But when
the number of IRQs are very large, it take very long time and 'cat
/proc/stat' takes more than 10 secs.  This is because sum of all irq
events are counted when /proc/stat is read.  This patch adds "sum of all
irq" counter percpu and reduce read costs.

The cost of reading /proc/stat is important because it's used by major
applications as 'top', 'ps', 'w', etc....

A test on a mechin (4096cpu, 256 nodes, 4592 irqs) shows

 %time cat /proc/stat > /dev/null
 Before Patch:  12.627 sec
 After  Patch:  2.459 sec
Signed-off-by: default avatarKAMEZAWA Hiroyuki <>
Tested-by: default avatarJack Steiner <>
Acked-by: default avatarJack Steiner <>
Cc: Yinghai Lu <>
Cc: Ingo Molnar <>
Cc: Thomas Gleixner <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 19cd56c4
......@@ -52,9 +52,7 @@ static int show_stat(struct seq_file *p, void *v)
guest = cputime64_add(guest, kstat_cpu(i).cpustat.guest);
guest_nice = cputime64_add(guest_nice,
for_each_irq_nr(j) {
sum += kstat_irqs_cpu(j, i);
sum += kstat_cpu_irqs_sum(i);
sum += arch_irq_stat_cpu(i);
for (j = 0; j < NR_SOFTIRQS; j++) {
......@@ -33,6 +33,7 @@ struct kernel_stat {
unsigned int irqs[NR_IRQS];
unsigned long irqs_sum;
unsigned int softirqs[NR_SOFTIRQS];
......@@ -54,6 +55,7 @@ static inline void kstat_incr_irqs_this_cpu(unsigned int irq,
struct irq_desc *desc)
static inline unsigned int kstat_irqs_cpu(unsigned int irq, int cpu)
......@@ -65,8 +67,9 @@ static inline unsigned int kstat_irqs_cpu(unsigned int irq, int cpu)
extern unsigned int kstat_irqs_cpu(unsigned int irq, int cpu);
#define kstat_irqs_this_cpu(DESC) \
#define kstat_incr_irqs_this_cpu(irqno, DESC) \
#define kstat_incr_irqs_this_cpu(irqno, DESC) do {\
kstat_this_cpu.irqs_sum++; } while (0)
......@@ -94,6 +97,13 @@ static inline unsigned int kstat_irqs(unsigned int irq)
return sum;
* Number of interrupts per cpu, since bootup
static inline unsigned int kstat_cpu_irqs_sum(unsigned int cpu)
return kstat_cpu(cpu).irqs_sum;
* Lock/unlock the current runqueue - to extract task statistics:
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