linux-kernel - Re: [git pull] scheduler fixes

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Message-ID: <20090131221939.GD29364@elte.hu>
Date:	Sat, 31 Jan 2009 23:19:39 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Alexey Zaytsev <alexey.zaytsev@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: [git pull] scheduler fixes


* Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> On Sat, 31 Jan 2009 19:08:47 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Sat, 2009-01-31 at 20:49 +0300, Alexey Zaytsev wrote:
> > > 
> > > And answering an earlier question, this happens only on i386 and only
> > > with 4K stacks because x86_64 dosn't have a separate softirq stack,
> > > so the preempt count diring the soft irq is at least IRQ_EXIT_OFFSET.
> > 
> > What do the other 30 odd architectures that Linux supports do? Is i386 
> > 4k really the _only_ with separate softirq stacks?
> 
> x86-64 and some of the other platforms could do with IRQ stacks but that 
> is another story.

64-bit x86 already has IRQ stacks [16K large, per CPU], separate from the 
8K syscall/process stack.

The question here is that on 64-bit hardirqs and softirqs share the same 
stack (it's large enough). On 32-bit we have them separated.

	Ingo
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