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

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Message-ID: <20101124190707.GG2815@redhat.com>
Date:	Wed, 24 Nov 2010 14:07:07 -0500
From:	Jason Baron <jbaron@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
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, Nov 24, 2010 at 07:39:30PM +0100, Peter Zijlstra wrote:
> 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?

perhaps, not. But I would like to better understand how expensive text
pokes are on some other arches such as powerpc first.

Obviously, I want the best implementation - the last posted version of
binary search, had a deadlock with the module_mutex, which I saw no
resolution for...

So, with this 1 additinal patch, we have a complete working implemenation of
jump labels within the current framework. We can iterate from there if ppl want
to simpify/optimize various parts. That's how I envision proceeding.

thanks,

-Jason
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