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Commit f2c66cd8 authored by KAMEZAWA Hiroyuki's avatar KAMEZAWA Hiroyuki Committed by Linus Torvalds
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/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 <kamezawa.hiroyu@jp.fujitsu.com>
Tested-by: default avatarJack Steiner <steiner@sgi.com>
Acked-by: default avatarJack Steiner <steiner@sgi.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 19cd56c4

fs/proc/stat.c

+1 −3
Original line number Diff line number Diff line
@@ -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,

			kstat_cpu(i).cpustat.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++) {

include/linux/kernel_stat.h

+12 −2
Original line number Diff line number Diff line
@@ -33,6 +33,7 @@ struct kernel_stat { 
#ifndef CONFIG_GENERIC_HARDIRQS

       unsigned int irqs[NR_IRQS];

#endif

	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)

{

	kstat_this_cpu.irqs[irq]++;

	kstat_this_cpu.irqs_sum++;

}



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) \

	((DESC)->kstat_irqs[smp_processor_id()])

#define kstat_incr_irqs_this_cpu(irqno, DESC) \

	((DESC)->kstat_irqs[smp_processor_id()]++)

#define kstat_incr_irqs_this_cpu(irqno, DESC) do {\

	((DESC)->kstat_irqs[smp_processor_id()]++);\

	kstat_this_cpu.irqs_sum++; } while (0)



#endif
@@ -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: