linux-kernel - Re: [PATCH 2/6] x86: allow to call text_poke

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Message-ID: <20131020154203.GN4118@linux.vnet.ibm.com>
Date:	Sun, 20 Oct 2013 08:42:03 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Petr Mladek <pmladek@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Kosina <jkosina@...e.cz>, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH 2/6] x86: allow to call text_poke_bp during boot

On Sat, Oct 19, 2013 at 06:02:39PM -0400, Steven Rostedt wrote:
> On Sat, 19 Oct 2013 14:33:50 -0700
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> 
> 
> > > > It's used to convert the calls to mcount to nops. But maybe a better
> > > > thing to do is to check if we only have a single CPU:
> > > > 
> > > > static void run_sync(void)
> > > > {
> > > > 	if (num_online_cpus() != 1)
> > > 
> > > Hmm, to be more robust to handle our future "ideal" machines, perhaps
> > > this should be:
> > > 
> > > 	/* Ideally we would like to run on zero CPUS! */
> > > 	if (num_online_cpus() < 2)
> > 
> 
> Bah! And for such a simple computation, I got it wrong.
> 
> 
> 	/* Ideally we would like to run on zero CPUS! */
> 	if (num_online_cpus > 1)
> 
> But I guess the question comes. If we are running on zero CPUS, should
> we perform the "on_each_cpu(do_sync_core, NULL, 1);" or not? Same goes
> with 5i-3 CPUS, or negative number CPUs. If we need to do on_each_cpu(),
> then I guess the != 1 will suffice.

Makes sense to me!  Whoever adds the ability to run on zero, negative,
or complex numbers of CPUs can adjust on_each_cpu() accordingly.

							Thanx, Paul

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