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

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Message-ID: <BLU0-SMTP501881B538D618099DC9C396D00@phx.gbl>
Date:	Mon, 14 Feb 2011 11:14:03 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Jason Baron <jbaron@...hat.com>
CC:	Peter Zijlstra <peterz@...radead.org>, 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

* Jason Baron (jbaron@...hat.com) wrote:
> On Mon, Feb 14, 2011 at 04:57:04PM +0100, Peter Zijlstra wrote:
> > On Mon, 2011-02-14 at 10:51 -0500, Jason Baron wrote:
> > > On Sat, Feb 12, 2011 at 07:47:45PM +0100, Peter Zijlstra wrote:
> > > > On Fri, 2011-02-11 at 22:38 +0100, Peter Zijlstra wrote:
> > > > > 
> > > > > So why can't we make that jump_label_entry::refcount and
> > > > > jump_label_key::state an atomic_t and be done with it? 
> > > > 
> > > > So I had a bit of a poke at this because I didn't quite understand why
> > > > all that stuff was as it was. I applied both Jason's patches and then
> > > > basically rewrote kernel/jump_label.c just for kicks ;-)
> > > > 
> > > > I haven't tried compiling this, let alone running it, but provided I
> > > > didn't actually forget anything the storage per key is now 16 bytes when
> > > > modules are disabled and 24 * (1 + mods) bytes for when they are
> > > > enabled. The old code had 64 + 40 * mods bytes.
> > > > 
> > > > I still need to clean up the static_branch_else bits and look at !x86
> > > > aside from the already mentioned bits.. but what do people think?
> > > > 
> > > > ---
> > > 
> > > Generally, I really like this! Its the direction I think the jump label
> > > code should be going. The complete removal of the hash table, makes the
> > > design a lot better and simpler. We just need to get some of the details
> > > cleaned up, and of course we need this to compile :) But I don't see any
> > > fundamental problems with this approach. 
> > > 
> > > Things that still need to be sorted out:
> > > 
> > > 1) Since jump_label.h, are included in kernel.h, (indirectly via the
> > > dynamic_debug.h) the atomic_t definitions could be problematic, since
> > > atomic.h includes kernel.h indirectly...so we might need some header
> > > magic.
> > 
> > Yes, I remember running into that when I did the jump_label_ref stuff,
> > some head-scratching is in order there.
> > 
> 
> yes. i suspect this might be the hardest bit of this...

I remember that atomic_t is defined in types.h now rather than atomic.h.
Any reason why you should keep including atomic.h from jump_label.h ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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