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

[Jason Baron]

On Wed, Nov 24, 2010 at 04:11:18PM +0100, Peter Zijlstra 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.
> 
> But but but, you're doing a friggin stop_machine to poke text, that's
> way more expensive than anything else.
> 

Yes, but other arches do not require stop_machine(). Also, there is work
for x86 to make the code patching happen without stop_machine().

> You can do away with the hash by using the bsearch stuff Andi has been
> proposing.
> 
> Also, I'd actually like to have more than 1 bit of storage, I'm using it
> as a general refcount.
> 
> 

Not a problem, we can have a few fields, the first of which can be a
pointer, the rest can be used for other purposes.

thanks,

-Jason

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