[linux-audio-dev] Re: [announce] [patch] Voluntary Kernel Preemption Patch

[Andrew Morton]

Andrea Arcangeli <andrea at suse.de> wrote:
>
> On Mon, Jul 12, 2004 at 05:08:44PM -0700, Andrew Morton wrote:
> > of code then it's pretty obvious what's happening.  If the trace is due to
> > a long irq-off time then it will point up into the offending
> > local_irq_enable().
> 
> schedule should be called with irq enabled, and I noticed here it's not
> (jnz work_resched is executed with irq off so there is a window for
> schedule to be called with irq off):
> 
> Index: linux-2.5/arch/i386/kernel/entry.S
> ===================================================================
> RCS file: /home/andrea/crypto/cvs/linux-2.5/arch/i386/kernel/entry.S,v
> retrieving revision 1.86
> diff -u -p -r1.86 entry.S
> --- linux-2.5/arch/i386/kernel/entry.S	23 May 2004 05:03:15 -0000	1.86
> +++ linux-2.5/arch/i386/kernel/entry.S	13 Jul 2004 04:21:55 -0000
> @@ -302,6 +310,7 @@ work_pending:
>  	testb $_TIF_NEED_RESCHED, %cl
>  	jz work_notifysig
>  work_resched:
> +	sti
>  	call schedule
>  	cli				# make sure we don't miss an interrupt
>  					# setting need_resched or sigpending

sys_sched_yield() also calls schedule() with local interrupts disabled. 
It's a bit grubby, but saves a few cycles.  Nick and Ingo prefer it that way.