linux-kernel - Re: [PATCH RFC V4 10/10] jump-label: initialize jump-label subsystem much earlier

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Message-ID: <20111013135945.GB2455@redhat.com>
Date:	Thu, 13 Oct 2011 09:59:47 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Steven Rostedt <rostedt@...dmis.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>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH RFC V4 10/10] jump-label: initialize jump-label subsystem
 much earlier

On Thu, Oct 13, 2011 at 12:43:48PM +0200, Peter Zijlstra wrote:
> On Wed, 2011-10-12 at 17:08 -0700, Jeremy Fitzhardinge wrote:
> > From: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> > 
> > Initialize jump_labels much earlier, we can use them.
> 
> We can use them, where? how? what?, that sentence just begs for more.
> 
> > diff --git a/init/main.c b/init/main.c
> > index 2a9b88a..f4094ed 100644
> > --- a/init/main.c
> > +++ b/init/main.c
> > @@ -637,6 +637,7 @@ asmlinkage void __init start_kernel(void)
> >  	acpi_early_init(); /* before LAPIC and SMP init */
> >  	sfi_init_late();
> >  
> > +	jump_label_init();
> >  	ftrace_init();
> >  
> >  	/* Do the rest non-__init'ed, we're now alive */
> 
> Can we push them much earlier still? If possible I'd like them to be
> before sched_init() so that I might use them there, if not possible, at
> the very least before enabling interrupts would be nice.
> 
> 

Yes, earlier still would be good. Also, it still bothers me a bit that
jump_label_inc()/dec() could be called and the branch not updated until
the jump label initialization. I feel like there should be a WARN() for
this case...ie:

jump_label_inc()/dec() {
	if (!jump_label_initialized)
		WARN("calling branch update before subsystem initialization");
}





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