On Wed, 12 Jul 2006 18:45:08 +0200
Martin Peschke <[email protected]> wrote:
> On Wed, 2006-07-12 at 09:10 -0700, Andrew Morton wrote:
> > On Wed, 12 Jul 2006 14:27:39 +0200
> > Martin Peschke <[email protected]> wrote:
> >
> > > +#define statistic_ptr(stat, cpu) \
> > > + ((struct percpu_data*)((stat)->data))->ptrs[(cpu)]
> >
> > This would be the only part of the kernel which uses percpu_data directly -
> > everything else uses the APIs (ie: per_cpu_ptr()). How come?
>
> The API, i.e. per_cpu_ptr(), doesn't allow to assign a value to any of
> the pointers in struct percpu_data. I need that capability because I
> make use of cpu hotplug notifications to fix per-cpu data at run time.
Fair enough, I guess.
> With regard to memory footprint this is much more efficient than using
> alloc_percpu().
How much storage are we talking about here? I find it a bit hard to work
that out.
> Is it be preferable to add something like set_per_cpu_ptr() to the API?
hm. Add a generic extension to a generic interface within a specific
subsystem versus doing it generically. Hard call ;)
I'd suggest that you:
- Create a new __alloc_percpu_mask(size_t size, cpumask_t cpus)
- Make that function use your newly added
percpu_data_populate(struct percpu_data *p, int cpu, size_t size, gfp_t gfp);
(maybe put `size' into 'struct percpu_data'?)
- implement __alloc_percpu() as __alloc_percpu_mask(size, cpu_possible_map)
- hack around madly until it compiles on uniprocessor.
-
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