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SubjectRe: [PATCH 0/2] jump label: 2.6.38 updates
* Jason Baron (jbaron@redhat.com) wrote:
> On Fri, Feb 11, 2011 at 05:20:25PM -0500, Mathieu Desnoyers wrote:
> > * 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
> >
>
> ok, I'll try and re-spin the interface based around atomic_t, if we are all
> agreed...there was also a circular dependency issue with atomic.h including
> kernel.h which included jump_label.h, and that was why we had a separate,
> jump_label_ref.h header file, but hopefully I can be resolve that in a clean
> way.

See spinlocks ?

jump_label_types.h (structure definitions, includes types.h,
included from kernel.h)
jump_label.h (prototypes, inline functions, includes atomic.h)

Thanks,

Mathieu

>
> thanks,
>
> -Jason

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


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