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/proc/stat: fix scalability of irq sum of all cpu

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In /proc/stat, the number of per-IRQ event is shown by making a sum each
irq's events on all cpus.  But we can make use of kstat_irqs().

kstat_irqs() do the same calculation, If !CONFIG_GENERIC_HARDIRQ,
it's not a big cost. (Both of the number of cpus and irqs are small.)

If a system is very big and CONFIG_GENERIC_HARDIRQ, it does

	for_each_irq()
		for_each_cpu()
			- look up a radix tree
			- read desc->irq_stat[cpu]
This seems not efficient. This patch adds kstat_irqs() for
CONFIG_GENRIC_HARDIRQ and change the calculation as

	for_each_irq()
		look up radix tree
		for_each_cpu()
			- read desc->irq_stat[cpu]

This reduces cost.

A test on (4096cpusp, 256 nodes, 4592 irqs) host (by Jack Steiner)

%time cat /proc/stat > /dev/null

Before Patch:	 2.459 sec
After Patch :	  .561 sec

[[email protected]: unexport kstat_irqs, coding-style tweaks]
[[email protected]: fix unused variable 'per_irq_sum']
Signed-off-by: KAMEZAWA Hiroyuki <[email protected]>
Tested-by: Jack Steiner <[email protected]>
Acked-by: Jack Steiner <[email protected]>
Cc: Yinghai Lu <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
KAMEZAWA Hiroyuki 2010-10-27 15:34:15 -07:00 • committed by Linus Torvalds
commit 478735e388
3 changed files with 21 additions and 8 deletions
Download patch file Download diff file Expand all files Collapse all files

10
fs/proc/stat.c
View file

@ -31,7 +31,6 @@ static int show_stat(struct seq_file *p, void *v)
u64 sum_softirq = 0;
unsigned int per_softirq_sums[NR_SOFTIRQS] = {0};
struct timespec boottime;
unsigned int per_irq_sum;
user = nice = system = idle = iowait =
irq = softirq = steal = cputime64_zero;
@ -108,13 +107,8 @@ static int show_stat(struct seq_file *p, void *v)
seq_printf(p, "intr %llu", (unsigned long long)sum);
/* sum again ? it could be updated? */
for_each_irq_nr(j) {
per_irq_sum = 0;
for_each_possible_cpu(i)
per_irq_sum += kstat_irqs_cpu(j, i);
seq_printf(p, " %u", per_irq_sum);
}
for_each_irq_nr(j)
seq_printf(p, " %u", kstat_irqs(j));
seq_printf(p,
"\nctxt %llu\n"