/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: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Tested-by: Jack Steiner <steiner@sgi.com>
Acked-by: Jack 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h
index c059044..8b9b890 100644
--- a/include/linux/kernel_stat.h
+++ b/include/linux/kernel_stat.h
@@ -33,6 +33,7 @@
#ifndef CONFIG_GENERIC_HARDIRQS
unsigned int irqs[NR_IRQS];
#endif
+ unsigned long irqs_sum;
unsigned int softirqs[NR_SOFTIRQS];
};
@@ -54,6 +55,7 @@
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 @@
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 @@
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: