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

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Date:	Wed, 24 Nov 2010 19:39:30 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jason Baron <jbaron@...hat.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Steven Rostedt <rostedt@...dmis.org>, mingo@...e.hu,
	hpa@...or.com, 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 1/3] jump label: add enabled/disabled state to jump
 label key entries

On Wed, 2010-11-24 at 13:24 -0500, Jason Baron wrote:
> By storing the state of the jump label with each key, we make
> sure that when modules are added, they are updated to the correct
> state. For example, if the kmalloc tracepoint is enabled and
> a module is added which has kmalloc, we make sure that the tracepoint
> is properly enabled on module load.
> 
> Also, if jump_label_enable(key), is called but the key has not yet
> been added to the hashtable of jump label keys, add 'key' to the table.
> In this way, if key value has its state updated, but we have not
> yet encountered a JUMP_LABEL() definition for it (if its located in
> a module), we ensure that the jump label is set to the correct
> state when it finally is encountered.
> 
> When modules are unloaded, we traverse the jump label hashtable,
> and remove any entries that have a key value that is contained
> by that module's text section. In this way key values are properly
> unregistered, and can be re-used.

So why again are we adding all this complexity? Does this really need to
be optimized in the face of how expensive text pokes are?
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