[PATCH] drop note_interrupt() for per-CPU for proper scaling
authorJohn Hawkes <hawkes@sgi.com>
Fri, 27 May 2005 19:53:00 +0000 (12:53 -0700)
committerLinus Torvalds <torvalds@ppc970.osdl.org>
Sat, 28 May 2005 18:14:00 +0000 (11:14 -0700)
commitb60c1f6ffd88850079ae419aa933ab0eddbd5535
treed0f12a263ea1fe3b434de6a5d338509e238d46b3
parent70ffc71c5c42c8ac62d951e80d9799bd5764f2f5
[PATCH] drop note_interrupt() for per-CPU for proper scaling

The "unhandled interrupts" catcher, note_interrupt(), increments a global
desc->irq_count and grossly damages scaling of very large systems, e.g.,
>192p ia64 Altix, because of this highly contented cacheline, especially
for timer interrupts.  384p is severely crippled, and 512p is unuseable.

All calls to note_interrupt() can be disabled by booting with "noirqdebug",
but this disables the useful interrupt checking for all interrupts.

I propose eliminating note_interrupt() for all per-CPU interrupts.  This
was the behavior of linux-2.6.10 and earlier, but in 2.6.11 a code
restructuring added a call to note_interrupt() for per-CPU interrupts.
Besides, note_interrupt() is a bit racy for concurrent CPU calls anyway, as
the desc->irq_count++ increment isn't atomic (which, if done, would make
scaling even worse).

Signed-off-by: John Hawkes <hawkes@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
kernel/irq/handle.c