Commit b60c1f6f authored by John Hawkes's avatar John Hawkes Committed by Linus Torvalds
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[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: default avatarJohn Hawkes <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 70ffc71c
...@@ -119,8 +119,6 @@ fastcall unsigned int __do_IRQ(unsigned int irq, struct pt_regs *regs) ...@@ -119,8 +119,6 @@ fastcall unsigned int __do_IRQ(unsigned int irq, struct pt_regs *regs)
*/ */
desc->handler->ack(irq); desc->handler->ack(irq);
action_ret = handle_IRQ_event(irq, regs, desc->action); action_ret = handle_IRQ_event(irq, regs, desc->action);
if (!noirqdebug)
note_interrupt(irq, desc, action_ret);
desc->handler->end(irq); desc->handler->end(irq);
return 1; return 1;
} }
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