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Date: Mon, 24 May 2004 17:10:48 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Ingo Molnar <mingo@elte.hu>
CC: Davide Libenzi <davidel@xmailserver.org>,
       Linux Kernel List <linux-kernel@vger.kernel.org>,
       rmk+lkml@arm.linux.org.uk
Subject: Re: scheduler: IRQs disabled over context switches
References: <20040523174359.A21153@flint.arm.linux.org.uk> <20040524083715.GA24967@elte.hu> <Pine.LNX.4.58.0405232340070.2676@bigblue.dev.mdolabs.com> <20040524090538.GA26183@elte.hu>
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Ingo Molnar wrote:
> * Davide Libenzi <davidel@xmailserver.org> wrote:
> 
> 
>>We used to do it in 2.4. What changed to make it fragile? The
>>threading (TLS) thing?
> 
> 
> it _should_ work, but in the past we only had trouble from such changes
> (at least in the O(1) tree of scheduling - 2.4 scheduler is OK.). We
> could try the patch below. It certainly boots on SMP x86. But it causes
> a 3.5% slowdown in lat_ctx so i'd not do it unless there are some really
> good reasons.
> 
> 	Ingo
> 
> --- linux/kernel/sched.c.orig	
> +++ linux/kernel/sched.c	
> @@ -247,9 +247,15 @@ static DEFINE_PER_CPU(struct runqueue, r
>   * Default context-switch locking:
>   */
>  #ifndef prepare_arch_switch
> -# define prepare_arch_switch(rq, next)	do { } while (0)
> -# define finish_arch_switch(rq, next)	spin_unlock_irq(&(rq)->lock)
> -# define task_running(rq, p)		((rq)->curr == (p))
> +# define prepare_arch_switch(rq, next)				\
> +		do {						\
> +			spin_lock(&(next)->switch_lock);	\
> +			spin_unlock(&(rq)->lock);		\

spin_unlock_irq?