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SubjectRe: [PATCH] Prevent nested interrupts when the IRQ stack is near overflowing v2

On Thu, 25 Mar 2010, Linus Torvalds wrote:
> NOTE! Historically, the "fast" handlers also had a much faster irq
> response because they didn't do that whole MASK/ACK/END thing. So they'd
> just keep the CPU interrupts disabled, and ACK at the end, and I think
> we've even used AUTOEIO so that they didn't need any ACK at all, and we
> never touched the interrupt controller itself for them.

Btw, it was even more extreme than that. The fast irq handlers got a
totally separate kernel entry point, and wouldn't save all registers, only
the compiler-clobbered ones. Which is why they then had no "struct
pt_regs" etc.

And yes, it really mattered. Then later we got so bloated that it wasn't
much of an issue - and just made everything more complicated.


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