linux-kernel - Re: [PATCH RFC V2 3/5] jump_label: if a key has already been initialized, don't nop it out

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Date:	Mon, 03 Oct 2011 11:47:26 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jason Baron <jbaron@...hat.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	"David S. Miller" <davem@...emloft.net>,
	David Daney <david.daney@...ium.com>,
	Michael Ellerman <michael@...erman.id.au>,
	Jan Glauber <jang@...ux.vnet.ibm.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Xen Devel <xen-devel@...ts.xensource.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	peterz@...radead.org
Subject: Re: [PATCH RFC V2 3/5] jump_label: if a key has already been
 initialized, don't nop it out

On Mon, 2011-10-03 at 11:02 -0400, Jason Baron wrote:

> if (!enabled)
> 	arch_jump_label_transform(iter, JUMP_LABEL_DISABLE);
> 
> 
> > +		if (iterk == key)
> >  			continue;
> >  
> > -		key = (struct jump_label_key *)(unsigned long)iter->key;
> > -		atomic_set(&key->enabled, 0);
> > +		key = iterk;
> >  		key->entries = iter;
> >  #ifdef CONFIG_MODULES
> >  		key->next = NULL;
> > @@ -212,7 +208,7 @@ void jump_label_apply_nops(struct module *mod)
> >  		return;
> >  
> >  	for (iter = iter_start; iter < iter_stop; iter++)
> > -		arch_jump_label_text_poke_early(iter->code);
> > +		arch_jump_label_transform(iter, JUMP_LABEL_DISABLE);
> >  }
> >  
> >  static int jump_label_add_module(struct module *mod)
> > -- 
> > 1.7.6.2
> > 
> 
> hmmm...this is used on module load in smp - so this would introduce a number of
> calls to stop_machine() where we didn't have them before. Yes, module
> load is a very slow path to begin with, but I think its at least worth
> pointing out...

And it is a good point to point out. As stop_machine becomes noticeable
by users on large scale CPU boxes. Ideally, we want to avoid stopmachine
when we do not need it.

-- Steve


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