Re: [PATCH] Cell SPU task notification

[Michael Ellerman <michael@ellerman.id.au>]

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> Subject: Enable SPU switch notification to detect currently active SPU tasks.
> 
> From: Maynard Johnson <maynardj@us.ibm.com>
> 
> This patch adds to the capability of spu_switch_event_register so that the
> caller is also notified of currently active SPU tasks.  It also exports
> spu_switch_event_register and spu_switch_event_unregister.

Hi Maynard,

It'd be really good if you could convince your mailer to send patches inline :)

> Index: linux-2.6.19-rc6-arnd1+patches/arch/powerpc/platforms/cell/spufs/sched.c
> ===================================================================
> --- linux-2.6.19-rc6-arnd1+patches.orig/arch/powerpc/platforms/cell/spufs/sched.c	2006-12-04 10:56:04.730698720 -0600
> +++ linux-2.6.19-rc6-arnd1+patches/arch/powerpc/platforms/cell/spufs/sched.c	2007-01-11 09:45:37.918333128 -0600
> @@ -46,6 +46,8 @@
>  
>  #define SPU_MIN_TIMESLICE 	(100 * HZ / 1000)
>  
> +int notify_active[MAX_NUMNODES];

You're basing the size of the array on MAX_NUMNODES
(1 << CONFIG_NODES_SHIFT), but then indexing it by spu->number.

It's quite possible we'll have a system with MAX_NUMNODES == 1, but > 1
spus, in which case this code is going to break. The PS3 is one such
system.

Instead I think you should have a flag in the spu struct.

>  #define SPU_BITMAP_SIZE (((MAX_PRIO+BITS_PER_LONG)/BITS_PER_LONG)+1)
>  struct spu_prio_array {
>  	unsigned long bitmap[SPU_BITMAP_SIZE];
> @@ -81,18 +83,45 @@
>  static void spu_switch_notify(struct spu *spu, struct spu_context *ctx)
>  {
>  	blocking_notifier_call_chain(&spu_switch_notifier,
> -			    ctx ? ctx->object_id : 0, spu);
> +				     ctx ? ctx->object_id : 0, spu);
> +}

Try not to make whitespace only changes in the same patch as actual code changes.

> +
> +static void notify_spus_active(void)
> +{
> +	int node;
> +	/* Wake up the active spu_contexts. When the awakened processes 
> +	 * sees their notify_active flag is set, they will call
> +	 * spu_notify_already_active().
> +	 */
> +	for (node = 0; node < MAX_NUMNODES; node++) {
> +		struct spu *spu;
> +		mutex_lock(&spu_prio->active_mutex[node]);
> +                list_for_each_entry(spu, &spu_prio->active_list[node], list) {
> +			struct spu_context *ctx = spu->ctx;
> +			wake_up_all(&ctx->stop_wq);
> +			notify_active[ctx->spu->number] = 1;
> +			smp_mb();
> +		}

I don't understand why you're setting the notify flag after you do the
wake_up_all() ?

You only need a smp_wmb() here.

Does the scheduler guarantee that ctxs won't swap nodes? Otherwise
between releasing the lock on one node and getting the lock on the next,
a ctx could migrate between them - which would cause either spurious
wake ups, or missing a ctx altogether. Although I'm not sure if it's
that important.

> +                mutex_unlock(&spu_prio->active_mutex[node]);
> +	}
> +	yield();
>  }
>  
>  int spu_switch_event_register(struct notifier_block * n)
>  {
> -	return blocking_notifier_chain_register(&spu_switch_notifier, n);
> +	int ret;
> +	ret = blocking_notifier_chain_register(&spu_switch_notifier, n);
> +	if (!ret)
> +		notify_spus_active();
> +	return ret;
>  }
> +EXPORT_SYMBOL_GPL(spu_switch_event_register);
>  
>  int spu_switch_event_unregister(struct notifier_block * n)
>  {
>  	return blocking_notifier_chain_unregister(&spu_switch_notifier, n);
>  }
> +EXPORT_SYMBOL_GPL(spu_switch_event_unregister);
>  
>  
>  static inline void bind_context(struct spu *spu, struct spu_context *ctx)
> @@ -250,6 +279,14 @@
>  	return spu_get_idle(ctx, flags);
>  }
>  
> +void spu_notify_already_active(struct spu_context *ctx)
> +{
> +	struct spu *spu = ctx->spu;
> +	if (!spu)
> +		return;
> +	spu_switch_notify(spu, ctx);
> +}
> +
>  /* The three externally callable interfaces
>   * for the scheduler begin here.
>   *
> Index: linux-2.6.19-rc6-arnd1+patches/arch/powerpc/platforms/cell/spufs/spufs.h
> ===================================================================
> --- linux-2.6.19-rc6-arnd1+patches.orig/arch/powerpc/platforms/cell/spufs/spufs.h	2007-01-08 18:18:40.093354608 -0600
> +++ linux-2.6.19-rc6-arnd1+patches/arch/powerpc/platforms/cell/spufs/spufs.h	2007-01-08 18:31:03.610345792 -0600
> @@ -183,6 +183,7 @@
>  void spu_yield(struct spu_context *ctx);
>  int __init spu_sched_init(void);
>  void __exit spu_sched_exit(void);
> +void spu_notify_already_active(struct spu_context *ctx);
>  
>  extern char *isolated_loader;
>  
> Index: linux-2.6.19-rc6-arnd1+patches/arch/powerpc/platforms/cell/spufs/run.c
> ===================================================================
> --- linux-2.6.19-rc6-arnd1+patches.orig/arch/powerpc/platforms/cell/spufs/run.c	2007-01-08 18:33:51.979311680 -0600
> +++ linux-2.6.19-rc6-arnd1+patches/arch/powerpc/platforms/cell/spufs/run.c	2007-01-11 10:17:20.777344984 -0600
> @@ -10,6 +10,8 @@
>  
>  #include "spufs.h"
>  
> +extern int notify_active[MAX_NUMNODES];
> +
>  /* interrupt-level stop callback function. */
>  void spufs_stop_callback(struct spu *spu)
>  {
> @@ -45,7 +47,9 @@
>  	u64 pte_fault;
>  
>  	*stat = ctx->ops->status_read(ctx);
> -	if (ctx->state != SPU_STATE_RUNNABLE)
> +	smp_mb();

And smp_rmb() should be sufficient here.

> +	if (ctx->state != SPU_STATE_RUNNABLE || notify_active[ctx->spu->number])
>  		return 1;
>  	spu = ctx->spu;
>  	pte_fault = spu->dsisr &
> @@ -319,6 +323,11 @@
>  		ret = spufs_wait(ctx->stop_wq, spu_stopped(ctx, &status));
>  		if (unlikely(ret))
>  			break;
> +		if (unlikely(notify_active[ctx->spu->number])) {
> +			notify_active[ctx->spu->number] = 0;
> +			if (!(status & SPU_STATUS_STOPPED_BY_STOP))
> +				spu_notify_already_active(ctx);
> +		}
>  		if ((status & SPU_STATUS_STOPPED_BY_STOP) &&
>  		    (status >> SPU_STOP_STATUS_SHIFT == 0x2104)) {
>  			ret = spu_process_callback(ctx);

cheers

-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person

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