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Date: Tue, 5 Mar 2002 00:43:25 +0000
From: Russell King <rmk@arm.linux.org.uk>
To: Robert Love <rml@tech9.net>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] 2.5: preemptive kernel on UP
Message-ID: <20020305004325.C32309@flint.arm.linux.org.uk>
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In-Reply-To: <1015287099.865.3.camel@phantasy>; from rml@tech9.net on Mon, Mar 04, 2002 at 07:11:23PM -0500
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On Mon, Mar 04, 2002 at 07:11:23PM -0500, Robert Love wrote:
> During 2.5.5-pre, an optimization was made that removed schedule_tail
> from UP kernels.  This causes the initial preempt_count of a new task,
> which starts at 1, to never decrement to zero and thus never become
> preemptible.
> 
> Thanks to everyone who pointed out the lousy performance - it took
> awhile to find but it should be fixed now.  Please comment if not.
> 
> Patch is against 2.5.6-pre2 and is critical for all UP+preempt users.
> 
> 	Robert Love
> 
> diff -urN linux-2.5.6-pre2/arch/alpha/kernel/entry.S linux/arch/alpha/kernel/entry.S
> --- linux-2.5.6-pre2/arch/alpha/kernel/entry.S	Fri Mar  1 17:21:14 2002
> +++ linux/arch/alpha/kernel/entry.S	Mon Mar  4 17:49:27 2002
> @@ -495,7 +495,7 @@
>  	ret	$31,($26),1
>  .end alpha_switch_to
>  
> -#ifdef CONFIG_SMP
> +#ifdef CONFIG_SMP || CONFIG_PREEMPT

Surely you really don't mean this?

-- 
Russell King (rmk@arm.linux.org.uk)                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html

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