On Friday 30 November 2007 17:43:06 Christoph Lameter wrote:
> Support an option
>
> CONFIG_PERCPU_ZERO_BASED
>
> that makes offsets for per cpu variables start at zero.
>
> If a percpu area starts at zero then
>
> 1. We do not need RELOC_HIDE anymore
Hi Christoph,
Why do you think this is true? You're still doing arithmetic on variable
addresses beyond the bound of the variable.
> 2. Indexes off the per cpu area for each processor are small
>
> 3. The percpu area "addresses" are offsets and we can then
> have allocpercpu/cpu_alloc in the future also use these
> offsets so that percpu functions can take any type of
> percpu address if it is provided by a percpu variable
> or a pointer obtained via allocpercpu/cpu_alloc.
This last point is orthogonal to offsetting at zero though...
> +#ifdef CONFIG_PERCPU_ZERO_BASED
> +extern char __per_cpu_load[];
> +extern char ____per_cpu_size[];
> +#define __per_cpu_size ((unsigned long)&____per_cpu_size)
> +#define __per_cpu_start ((char *)0)
> +#define __per_cpu_end ((char *)__per_cpu_size)
> +#else
> extern char __per_cpu_start[], __per_cpu_end[];
> +#define __per_cpu_load __per_cpu_start
> +#define __per_cpu_size (__per_cpu_end - __per_cpu_start)
> +#endif
Hmm, can't you just define __per_cpu_start and __per_cpu_end in the linker
script and fold this code back together again?
> for_each_possible_cpu(i) {
> - start = (unsigned long) &__per_cpu_start + per_cpu_offset(i);
> - end = (unsigned long) &__per_cpu_start + PERCPU_ENOUGH_ROOM
> + start = (unsigned long) __per_cpu_start + per_cpu_offset(i);
> + end = (unsigned long) __per_cpu_start + PERCPU_ENOUGH_ROOM
> + per_cpu_offset(i);
I found the original clearer; why change it?
Cheers,
Rusty.
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