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Subject: Re: [PATCH] softirq: Avoid stack switch from ksoftirqd
From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
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Date: Wed, 02 Feb 2011 17:24:56 +0100
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On Wed, 2011-02-02 at 17:10 +0100, Thomas Gleixner wrote:
> ksoftirqd() calls do_softirq() which switches stacks on several
> architectures. That makes no sense at all. ksoftirqd's stack is
> sufficient.
> 
> Call __do_softirq() directly.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

> ---
>  kernel/softirq.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6-tip/kernel/softirq.c
> ===================================================================
> --- linux-2.6-tip.orig/kernel/softirq.c
> +++ linux-2.6-tip/kernel/softirq.c
> @@ -738,7 +738,10 @@ static int run_ksoftirqd(void * __bind_c
>  			   don't process */
>  			if (cpu_is_offline((long)__bind_cpu))
>  				goto wait_to_die;
> -			do_softirq();
> +			local_irq_disable();
> +			if (local_softirq_pending())
> +				__do_softirq();
> +			local_irq_enable();
>  			preempt_enable_no_resched();
>  			cond_resched();
>  			preempt_disable();