linux-kernel - Re: [PATCH] Force rcutorture tasks to spread over CPUs

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Message-ID: <20070627163025.GB8604@linux.vnet.ibm.com>
Date:	Wed, 27 Jun 2007 09:30:25 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, josh@...edesktop.org,
	dipankar@...ibm.com
Subject: Re: [PATCH] Force rcutorture tasks to spread over CPUs

On Wed, Jun 27, 2007 at 08:30:55AM +0200, Ingo Molnar wrote:
> 
> * Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > On Tue, 12 Jun 2007 21:28:04 -0700
> > "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> > 
> > > +	while (!startwriters)
> > > +		barrier();	/* Force scheduler to spread over CPUs. */
> > 
> > one wonders whether a cpu_relax() would be a bit nicer here.  That 
> > implicitly does a barrier().
> > 
> > This patch doesn't make much sense for non-SMP builds?
> 
> i think this patch should be unnecessary because we found the real SMP 
> balancing bug in the upstream scheduler causing this rcu problem, see:
> 
>  commit 92c4ca5c3a5e180e9762438db235f41d192cb955
>  Author: Christoph Lameter <clameter@....com>
>  Date:   Sat Jun 23 17:16:33 2007 -0700
> 
>      sched: fix next_interval determination in idle_balance()

Ingo is correct -- applying the above patch caused the scheduler to
correctly balance the rcutorture tasks, so that my patch to rcutorture
is no longer needed.  Which is a very good thing!  ;-)

							Thanx, Paul
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