Date: Wed, 25 May 2005 05:24:00 -0700
From: Andrew Morton <akpm@osdl.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: nickpiggin@yahoo.com.au, linux-kernel@vger.kernel.org
Subject: Re: [patch] remove set_tsk_need_resched() from init_idle()
Message-Id: <20050525052400.46bccf26.akpm@osdl.org>
In-Reply-To: <20050524154230.GA17814@elte.hu>
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	<42934748.8020501@yahoo.com.au>
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	<20050524154230.GA17814@elte.hu>
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Ingo Molnar <mingo@elte.hu> wrote:
>
> ..
>
> this patch (ontop of the current -mm scheduler patchset) tweaks 
> cpu_idle() semantics a bit: it changes the idle loops (that do 
> preemption) to call the first schedule() unconditionally.
> 
> the advantage is that as a result we dont have to set the idle thread's 
> NEED_RESCHED flag in init_idle(), which in turn makes cond_resched() 
> even more of an invariant: it can be called even from init code without 
> it having any effect. A cond resched in the init codepath hangs 
> otherwise.
> 
> this patch, while having no negative side-effects, enables wider use of 
> cond_resched()s. (which might happen in the stock kernel too, but it's 
> particulary important for voluntary-preempt) (note that for now this 
> patch only covers architectures that use kernel/Kconfig.preempt, but all 
> other architectures will work just fine too.)
> 
> --- linux/arch/x86_64/kernel/process.c.orig
> +++ linux/arch/x86_64/kernel/process.c
> @@ -162,6 +162,8 @@ EXPORT_SYMBOL_GPL(cpu_idle_wait);
>   */
>  void cpu_idle (void)
>  {
> +	set_tsk_need_resched(current);
> +
>  	/* endless idle loop with no priority at all */
>  	while (1) {
>  		while (!need_resched()) {

ia64 needed this treatment also to fix a hang during boot.  u o me 3 hrs.

Are all the other architectures busted as well?
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