linux/kernel/irq
KAMEZAWA Hiroyuki 478735e388 /proc/stat: fix scalability of irq sum of all cpu
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

[akpm@linux-foundation.org: unexport kstat_irqs, coding-style tweaks]
[akpm@linux-foundation.org: fix unused variable 'per_irq_sum']
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>
2010-10-27 18:03:13 -07:00
..
Kconfig genirq: Remove the now unused sparse irq leftovers 2010-10-12 16:53:44 +02:00
Makefile genirq: Remove the now unused sparse irq leftovers 2010-10-12 16:53:44 +02:00
autoprobe.c genirq: Provide compat handling for chip->set_type() 2010-10-04 12:43:47 +02:00
chip.c genirq: Sanitize dynamic irq handling 2010-10-12 16:53:44 +02:00
devres.c devres/irq: Fix devm_irq_match comment 2010-02-11 16:01:02 +01:00
dummychip.c genirq: Fix CONFIG_GENIRQ_NO_DEPRECATED=y build 2010-10-12 21:59:55 +02:00
handle.c genirq: Distangle kernel/irq/handle.c 2010-10-12 16:39:05 +02:00
internals.h genirq: Remove the now unused sparse irq leftovers 2010-10-12 16:53:44 +02:00
irqdesc.c /proc/stat: fix scalability of irq sum of all cpu 2010-10-27 18:03:13 -07:00
manage.c genirq: Provide compat handling for chip->set_wake() 2010-10-04 12:43:48 +02:00
migration.c genirq: Provide compat handling for chip->set_affinity() 2010-10-04 12:43:46 +02:00
pm.c genirq: Convert irq_desc.lock to raw_spinlock 2009-12-14 23:55:33 +01:00
proc.c genirq: Prepare proc for real sparse irq support 2010-10-12 16:39:07 +02:00
resend.c genirq: Provide compat handling for chip->retrigger() 2010-10-04 12:43:50 +02:00
spurious.c genirq: Provide config option to disable deprecated code 2010-10-04 13:40:24 +02:00