linux-kernel - Re: CPU Hotplug rework

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Message-ID: <20120411010015.GA2402@linux.vnet.ibm.com>
Date:	Tue, 10 Apr 2012 18:00:22 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arjan van de Ven <arjan@...radead.org>,
	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Milton Miller <miltonm@....com>,
	"mingo@...e.hu" <mingo@...e.hu>, Tejun Heo <tj@...nel.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Linux PM mailing list <linux-pm@...r.kernel.org>
Subject: Re: CPU Hotplug rework

On Tue, Apr 10, 2012 at 08:37:18PM -0400, Steven Rostedt wrote:
> On Tue, 2012-04-10 at 17:28 -0700, Paul E. McKenney wrote:
> 
> > > Just to throw out the stupid silly approach.
> > > 
> > > What about creating a "__register_cpu_notifier()" that just does:
> > > 
> > > int __ref __register_cpu_notifier(struct notifier_block *nb)
> > > {
> > > 	return raw_notifier_chain_register(&cpu_chain, nb);
> > > }
> > > 
> > > Also making cpu_maps_update_begin/done() global (and probably rename
> > > them).
> 
> I just noticed that the cpu_maps_update_begin/done() are already global.
> 
> > > 
> > > and then in the above code do:
> > > 
> > > 	cpu_maps_update_begin();
> > > 	__register_cpu_notifier(nb);
> > > 	do_setup();
> > > 	cpu_maps_update_done();
> > > 
> > > 
> > > Just saying,
> > 
> > That does have some attractive properties, now that you mention it.  ;-)
> 
> Which property? Stupid or Silly ;-)

As with any piece of software, no matter how small, both.  ;-)

Of course, __register_cpu_notifier() would need lockdep checking to make
sure that it wasn't called without the benefit of cpu_maps_update_begin().
I might be missing something, but as long as that was in place, seems
like it is a lot simpler and easier to use than the alternatives that
Srivatsa and I were kicking around.

							Thanx, Paul

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