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Date: Sat, 31 Jan 2009 23:19:39 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Peter Zijlstra <peterz@infradead.org>,
       Alexey Zaytsev <alexey.zaytsev@gmail.com>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
       Nick Piggin <npiggin@suse.de>
Subject: Re: [git pull] scheduler fixes
Message-ID: <20090131221939.GD29364@elte.hu>
References: <20090130230936.GA7549@elte.hu> <1233421901.4787.27.camel@laptop> <1233422632.4787.31.camel@laptop> <f19298770901310949m7aabf7bcp219ae4cc5d1b363b@mail.gmail.com> <1233425327.4787.35.camel@laptop> <20090131212106.6e2e05b0@lxorguk.ukuu.org.uk>
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* Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:

> On Sat, 31 Jan 2009 19:08:47 +0100
> Peter Zijlstra <peterz@infradead.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