Re: [PATCH 1/2] generic smp function call: add multiple queues forscaling

[Jeremy Fitzhardinge]

Andi Kleen wrote:
> Ah I see the locking is here. Never mind the earlier comment.
>
>   
> > +#define	NQUEUES	CONFIG_GENERIC_SMP_QUEUES
> > +#else
> > +#define	NQUEUES	1
> > +#endif
> > +
> > static DEFINE_PER_CPU(struct call_single_queue, call_single_queue);
> > -static LIST_HEAD(call_function_queue);
> > -__cacheline_aligned_in_smp DEFINE_SPINLOCK(call_function_lock);
> > +struct queue {
> > +	struct list_head list;
> > +	spinlock_t lock;
> > +};
> > +
> > +static __cacheline_aligned_in_smp struct queue 
> > call_function_queues[NQUEUES];
> >     
>
> Hmm are you sure this aligns the individual elements and not the whole
> array? 
>   

Hm, that's a point.  I guess the __cacheline_aligned_in_smp should be on 
the struct definition.

> > +static int __init init_smp_function_call(void)
> > +{
> > +	int i;
> > +
> > +	for(i = 0; i < NQUEUES; i++) {
> > +		INIT_LIST_HEAD(&call_function_queues[i].list);
> > +		spin_lock_init(&call_function_queues[i].lock);
> > +	}
> > +
> > +	return 0;
> > +}
> > +early_initcall(init_smp_function_call);
> >     
>
> You can avoid all that init gunk by using the [0 ... NQUEUES] = ..
> gcc extension in the initializer.
>   

Are you sure?  I tried using it, but couldn't work out how.  Remember 
the list head init needs to point to itself, which means it's not 
constant across the array.

   J
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