Subject: Re: [PATCH 2.6.10-mm2] Use the new preemption code [2/3] Resend
From: Thomas Gleixner <tglx@linutronix.de>
Reply-To: tglx@linutronix.de
To: Ingo Molnar <mingo@elte.hu>
Cc: Russell King <rmk+lkml@arm.linux.org.uk>,
       LKML <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@osdl.org>
In-Reply-To: <20050110110252.GA1605@elte.hu>
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	 <20050110094624.A24919@flint.arm.linux.org.uk>
	 <1105351977.3058.2.camel@lap02.tec.linutronix.de>
	 <20050110110252.GA1605@elte.hu>
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Date: Mon, 10 Jan 2005 14:46:09 +0100
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On Mon, 2005-01-10 at 12:02, Ingo Molnar wrote:
> i wouldnt raise this issue if it was the name only, but there's more to
> preempt_schedule_irq() than its name: it gets called with irqs off and
> the scheduler returns with irqs off and with a guarantee that there is
> no (irq-generated) pending preemption request for this task right now. 
> I.e. the checks for need_resched can be skipped, and interrupts dont
> have to be disabled to do a safe return-to-usermode (as done on some
> architectures).
> 
> as far as i can see do_preempt_schedule() doesnt have these properties:
> what it guarantees is that it avoids the preemption recursion via the
> lowlevel code doing the PREEMPT_ACTIVE setting.
> 
> lets agree upon a single, common approach. I went for splitting up
> preempt_schedule() into two variants: the 'synchronous' one (called
> preempt_schedule()) is only called from syscall level and has no
> repeat-preemption and hence stack-recursion worries. The 'asynchronous'
> one (called preempt_schedule_irq()) is called from asynchronous contexts
> (hardirq events) and is fully ready to deal with all the reentrancy
> situations that may occur. It's careful about not re-enabling
> interrupts, etc.

Sure, I guessed that from your short description that it implies more
than the seperation I have done. I have no objection against your
approach at all.

tglx


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