linux_dsm_epyc7002/include
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
..
acpi Merge branch 'misc' into release 2010-10-26 14:51:00 -04:00
asm-generic gpiolib: fix HAVE_GPIO_LIB leftovers in asm-generic/gpio.h 2010-10-27 18:03:06 -07:00
crypto Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2010-10-24 13:41:39 -07:00
drm Merge remote branch 'intel/drm-intel-next' of ../drm-next into drm-core-next 2010-10-26 09:23:22 +10:00
keys
linux /proc/stat: fix scalability of irq sum of all cpu 2010-10-27 18:03:13 -07:00
math-emu
media Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input 2010-10-25 07:59:01 -07:00
mtd
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next-2.6 2010-10-23 11:47:02 -07:00
pcmcia pcmcia: IOCARD is also required for using IRQs 2010-10-22 08:46:36 +02:00
rdma IB/core: Add VLAN support for IBoE 2010-10-25 10:20:39 -07:00
rxrpc
scsi Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/roland/infiniband 2010-10-26 17:54:22 -07:00
sound Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-2.6 2010-10-25 08:32:05 -07:00
trace writeback: do not sleep on the congestion queue if there are no congested BDIs or if significant congestion is not being encountered in the current zone 2010-10-26 16:52:07 -07:00
video Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-2.6 2010-10-25 08:32:05 -07:00
xen Merge branches 'upstream/xenfs' and 'upstream/core' of git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen 2010-10-26 18:20:19 -07:00
Kbuild