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

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Message-ID: <1290612112.2072.484.camel@laptop>
Date:	Wed, 24 Nov 2010 16:21:52 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Jason Baron <jbaron@...hat.com>, mingo@...e.hu,
	mathieu.desnoyers@...ymtl.ca, 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 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.

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