From: <ha...@sg...> - 2005-05-25 23:20:07
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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 <ha...@sg...> --- Index: linux/kernel/irq/handle.c =================================================================== --- linux.orig/kernel/irq/handle.c 2005-03-01 23:38:37.000000000 -0800 +++ linux/kernel/irq/handle.c 2005-05-18 11:02:18.000000000 -0700 @@ -118,8 +118,6 @@ */ 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; } |