From: John Hawkes Date: Fri, 27 May 2005 19:53:00 +0000 (-0700) Subject: [PATCH] drop note_interrupt() for per-CPU for proper scaling X-Git-Tag: v2.6.12-rc6~128 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b60c1f6ffd88850079ae419aa933ab0eddbd5535;p=linux-2.6 [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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c index 06b5a63239..436c7d93c0 100644 --- a/kernel/irq/handle.c +++ b/kernel/irq/handle.c @@ -119,8 +119,6 @@ fastcall unsigned int __do_IRQ(unsigned int irq, struct pt_regs *regs) */ desc->handler->ack(irq); action_ret = handle_IRQ_event(irq, regs, desc->action); - if (!noirqdebug) - note_interrupt(irq, desc, action_ret); desc->handler->end(irq); return 1; }