Re: [PATCH 1/3] jump label: add enabled/disabled state to jump label key entries

[Peter Zijlstra <peterz@infradead.org>]

On Wed, 2010-11-24 at 10:15 -0500, Steven Rostedt wrote:
> On Wed, 2010-11-24 at 09:54 -0500, Jason Baron wrote:
> > On Wed, Nov 24, 2010 at 09:20:09AM +0100, Peter Zijlstra wrote:
> > > On Tue, 2010-11-23 at 16:27 -0500, Jason Baron wrote:
> > > >         struct hlist_head modules;
> > > >         unsigned long key;
> > > > +       u32 nr_entries : 31,
> > > > +              enabled :  1;
> > > >  }; 
> > > 
> > > I still don't see why you do this, why not simply mandate that the key
> > > is of type atomic_t* and use *key as enabled state?
> > > 
> > 
> > Because I want to use *key as a pointer directly to 'struct jump_label_entry'.
> > In this way jump_label_enable(), jump_label_disable(), become O(1) operations.
> > That way we don't need any hashing.
> 
> I'm curious, how are you going to get the keys to point to the jump
> label structures?

What jump label structure, we've got the section with:

 {key-address, text-address}

tuples, keep that sorted and binary search it,. voila!

You don't need extra data, but since we have to have some data to have a
key-address, use that storage for a simple refcount.