linux-kernel - Re: [PATCH tip/core/rcu 08/15] rcu: Apply for_each_rcu_flavor() to increment_cpu_stall

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Message-ID: <20120904224442.GS2593@linux.vnet.ibm.com>
Date:	Tue, 4 Sep 2012 15:44:42 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, sbw@....edu, patches@...aro.org
Subject: Re: [PATCH tip/core/rcu 08/15] rcu: Apply for_each_rcu_flavor() to
 increment_cpu_stall_ticks()

On Fri, Aug 31, 2012 at 11:15:16AM -0700, Josh Triplett wrote:
> On Thu, Aug 30, 2012 at 11:56:21AM -0700, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> > 
> > The increment_cpu_stall_ticks() function listed each RCU flavor
> > explicitly, with an ifdef to handle preemptible RCU.  This commit
> > therefore applies for_each_rcu_flavor() to save a line of code.
> 
> And also mysteriously changes __get_cpu_var to __this_cpu_var without
> documenting that (or the reason for it) in the commit message. :)

Good point!  The change is needed because of the need to switch from
using the given rcu_data per-CPU variable directly to accessing it via
each rcu_state structure's ->rda pointer.  Will update the commit log.

							Thanx, Paul

> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > ---
> >  kernel/rcutree_plugin.h |    9 ++++-----
> >  1 files changed, 4 insertions(+), 5 deletions(-)
> > 
> > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
> > index 3ea60c9..139a803 100644
> > --- a/kernel/rcutree_plugin.h
> > +++ b/kernel/rcutree_plugin.h
> > @@ -2196,11 +2196,10 @@ static void zero_cpu_stall_ticks(struct rcu_data *rdp)
> >  /* Increment ->ticks_this_gp for all flavors of RCU. */
> >  static void increment_cpu_stall_ticks(void)
> >  {
> > -	__get_cpu_var(rcu_sched_data).ticks_this_gp++;
> > -	__get_cpu_var(rcu_bh_data).ticks_this_gp++;
> > -#ifdef CONFIG_TREE_PREEMPT_RCU
> > -	__get_cpu_var(rcu_preempt_data).ticks_this_gp++;
> > -#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
> > +	struct rcu_state *rsp;
> > +
> > +	for_each_rcu_flavor(rsp)
> > +		__this_cpu_ptr(rsp->rda)->ticks_this_gp++;
> >  }
> >  
> >  #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
> > -- 
> > 1.7.8
> > 
> 

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