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SubjectRe: [PATCH 0/2] jump label: 2.6.38 updates
* Peter Zijlstra (peterz@infradead.org) wrote:
> On Fri, 2011-02-11 at 16:13 -0500, Mathieu Desnoyers wrote:
> >
> > Thoughts ?
>
> #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
> +
> +struct jump_label_key {
> + void *ptr;
> +};
>
> struct jump_label_entry {
> struct hlist_node hlist;
> struct jump_entry *table;
> - int nr_entries;
> /* hang modules off here */
> struct hlist_head modules;
> unsigned long key;
> + u32 nr_entries;
> + int refcount;
> };
>
> #else
>
> +struct jump_label_key {
> + int state;
> +};
>
> #endif
>
> So why can't we make that jump_label_entry::refcount and
> jump_label_key::state an atomic_t and be done with it?
>
> Then the enabled case uses if (atomic_inc_return(&key->ptr->refcount) ==
> 1), and the disabled atomic_inc(&key->state).
>

OK, by "enabled" you mean #if defined(CC_HAVE_ASM_GOTO) &&
defined(CONFIG_JUMP_LABEL), and "disabled", the #else.

I guess the only downside is the extra volatile for the atomic_read for
the fallback case, which is not really much of problem realistically
speaking: anyway, the volatile is a good thing to have in the fallback
case to force the compiler to re-read the variable. Let's go with your
idea.

Thanks,

Mathieu


--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com


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