[PATCH 1/3 v2] softirq: Introduce statistics for softirq

Keika Kobayashi
2008-11-22T04:25:53Z

Statistics for softirq doesn't exist.
It will be helpful like statistics for interrupts.
This patch introduces counting the number of softirq,
which will be exported in /proc/softirqs.

When softirq handler consumes much CPU time,
/proc/stat is like the following.

$ while :; do cat /proc/stat | head -n1 ; sleep 10 ; done
cpu 88 0 408 739665 583 28 2 0 0
cpu 450 0 1090 740970 594 28 1294 0 0
^^^^
softirq

In such a situation,
/proc/softirqs shows us which softirq handler is invoked.
We can see the increase rate of softirqs.

<before>
$ cat /proc/softirqs
CPU0 CPU1 CPU2 CPU3
HI 0 0 0 0
TIMER 462850 462805 462782 462718
NET_TX 0 0 0 365
NET_RX 2472 2 2 40
BLOCK 0 0 381 1164
TASKLET 0 0 0 224
SCHED 462654 462689 462698 462427
RCU 3046 2423 3367 3173

<after>
$ cat /proc/softirqs
CPU0 CPU1 CPU2 CPU3
HI 0 0 0 0
TIMER 463361 465077 465056 464991
NET_TX 53 0 1 365
NET_RX 3757 2 2 40
BLOCK 0 0 398 1170
TASKLET 0 0 0 224
SCHED 463074 464318 464612 463330
RCU 3505 2948 3947 3673

When CPU TIME of softirq is high,
the rates of increase is the following.
TIMER : 220/sec : CPU1-3
NET_TX : 5/sec : CPU0
NET_RX : 120/sec : CPU0
SCHED : 40-200/sec : all CPU
RCU : 45-58/sec : all CPU

The rates of increase in an idle mode is the following.
TIMER : 250/sec
SCHED : 250/sec
RCU : 2/sec

It seems many softirqs for receiving packets and rcu are invoked.
This gives us help for checking system.

Signed-off-by: Keika Kobayashi <kobayashi.kk@ncos.nec.co.jp>
Reviewed-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
---
include/linux/kernel_stat.h | 12 ++++++++++++
kernel/softirq.c | 1 +
2 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h
index 4a145ca..57c1643 100644
--- a/include/linux/kernel_stat.h
+++ b/include/linux/kernel_stat.h
@@ -5,6 +5,7 @@
#include <linux/threads.h>
#include <linux/percpu.h>
#include <linux/cpumask.h>
+#include <linux/interrupt.h>
#include <asm/irq.h>
#include <asm/cputime.h>

@@ -29,6 +30,7 @@ struct cpu_usage_stat {
struct kernel_stat {
struct cpu_usage_stat cpustat;
unsigned int irqs[NR_IRQS];
+ unsigned int softirqs[NR_SOFTIRQS];
};

DECLARE_PER_CPU(struct kernel_stat, kstat);
@@ -52,6 +54,16 @@ static inline unsigned int kstat_irqs_cpu(unsigned int irq, int cpu)
return kstat_cpu(cpu).irqs[irq];
}

+static inline void kstat_incr_softirqs_this_cpu(unsigned int irq)
+{
+ kstat_this_cpu.softirqs[irq]++;
+}
+
+static inline unsigned int kstat_softirqs_cpu(unsigned int irq, int cpu)
+{
+ return kstat_cpu(cpu).softirqs[irq];
+}
+
/*
* Number of interrupts per specific IRQ source, since bootup
*/
diff --git a/kernel/softirq.c b/kernel/softirq.c
index e7c69a7..088e179 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -208,6 +208,7 @@ restart:
do {
if (pending & 1) {
int prev_count = preempt_count();
+ kstat_incr_softirqs_this_cpu(h - softirq_vec);

h->action(h);

--
1.5.0.6