linux-kernel - Re: [PATCH 0/2] jump label: 2.6.38 updates

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Date:	Fri, 11 Feb 2011 20:25:28 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jason Baron <jbaron@...hat.com>
Cc:	mathieu.desnoyers@...ymtl.ca, hpa@...or.com, rostedt@...dmis.org,
	mingo@...e.hu, tglx@...utronix.de, andi@...stfloor.org,
	roland@...hat.com, rth@...hat.com, masami.hiramatsu.pt@...achi.com,
	fweisbec@...il.com, avi@...hat.com, davem@...emloft.net,
	sam@...nborg.org, ddaney@...iumnetworks.com,
	michael@...erman.id.au, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] jump label: 2.6.38 updates

On Wed, 2011-01-05 at 10:43 -0500, Jason Baron wrote:
> Hi,
> 
> The first patch uses the storage space of the jump label key address
> as a pointer into the update table. In this way, we can find all
> the addresses that need to be updated without hashing.
> 
> The second patch introduces:
> 
> static __always_inline bool static_branch(struct jump_label_key *key);
> 
> instead of the old JUMP_LABEL(key, label) macro.
> 
> In this way, jump labels become really easy to use:
> 
> Define:
> 
>         struct jump_label_key jump_key;
> 
> Can be used as:
> 
>         if (static_branch(&jump_key))
>                 do unlikely code
> 
> enable/disale via:
> 
>         jump_label_enable(&jump_key);
>         jump_label_disable(&jump_key);
> 
> that's it!
> 
> For perf, which also uses jump labels, I've left the reference counting
> out of the jump label layer, thus removing the 'jump_label_inc()' and
> 'jump_label_dec()' interface. Hopefully, this is a more palatable solution.

Right, lets go with this. Maybe we'll manage to come up with something
saner than _else_atomic_read(), but for now its an improvement over what
we have.

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