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Date: Thu, 5 Feb 2009 01:12:42 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Alexey Zaytsev <alexey.zaytsev@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
       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: <20090205001242.GC15680@elte.hu>
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* Alexey Zaytsev <alexey.zaytsev@gmail.com> wrote:

> On Mon, Feb 2, 2009 at 12:52, 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.
> >
> > Which suggests that an initial preempt_count offset of 1 should suffice
> > to fix this issue and not confuse the softirq tracing, hmm?
> 
> Can't we just copy the preempt count when switching stacks?

that always has a dynamic cost and the thing is that after-switch we are 
fine with a constant count.

	Ingo