Re: scheduler: IRQs disabled over context switches

[Nick Piggin]

Ingo Molnar wrote:
> * Davide Libenzi <davidel@xxxxxxxxxxxxxxx> 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?
-
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