linux-kernel - Re: [PATCH] Prevent nested interrupts when the IRQ stack is near overflowing v2

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Date:	Thu, 25 Mar 2010 09:17:13 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Thomas Gleixner <tglx@...utronix.de>
cc:	Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
	LKML <linux-kernel@...r.kernel.org>, jesse.brandeburg@...el.com
Subject: Re: [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.

		Linus
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