linux-kernel - Re: [PATCH] context_tracking: New context tracking susbsystem

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Date:	Thu, 29 Nov 2012 03:36:27 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Li Zhong <zhong@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Gilad.Ben-Yossef.gilad@...yossef.com
Subject: Re: [PATCH] context_tracking: New context tracking susbsystem

On Thu, Nov 29, 2012 at 11:30:19AM +0100, Frederic Weisbecker wrote:
> 2012/11/29 Li Zhong <zhong@...ux.vnet.ibm.com>:
> > On Tue, 2012-11-27 at 19:33 +0100, Frederic Weisbecker wrote:
> > [....]
> >> -
> >> -     WARN_ON_ONCE(!current->mm);
> >> -
> >> -     local_irq_save(flags);
> >> -     rdtp = &__get_cpu_var(rcu_dynticks);
> >> -     if (!rdtp->ignore_user_qs && !rdtp->in_user) {
> >> -             rdtp->in_user = true;
> >> -             rcu_eqs_enter(true);
> >> -     }
> >
> > It seems to me that ignore_user_qs and in_user defined in struct
> > rcu_dynticks are no longer needed?
> >
> > If so, then maybe we could remove them, code below:
> >
> > ==========
> > diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> > index e441b77..b8fae5d 100644
> > --- a/kernel/rcutree.c
> > +++ b/kernel/rcutree.c
> > @@ -2719,9 +2719,6 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
> >         rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
> >         WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
> >         WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
> > -#ifdef CONFIG_RCU_USER_QS
> > -       WARN_ON_ONCE(rdp->dynticks->in_user);
> > -#endif
> >         rdp->cpu = cpu;
> >         rdp->rsp = rsp;
> >         rcu_boot_init_nocb_percpu_data(rdp);
> > diff --git a/kernel/rcutree.h b/kernel/rcutree.h
> > index 4b69291..6f21f2e 100644
> > --- a/kernel/rcutree.h
> > +++ b/kernel/rcutree.h
> > @@ -102,10 +102,6 @@ struct rcu_dynticks {
> >                                     /* idle-period nonlazy_posted snapshot. */
> >         int tick_nohz_enabled_snap; /* Previously seen value from sysfs. */
> >  #endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */
> > -#ifdef CONFIG_RCU_USER_QS
> > -       bool ignore_user_qs;        /* Treat userspace as extended QS or not */
> > -       bool in_user;               /* Is the CPU in userland from RCU POV? */
> > -#endif
> >  };
> >
> >  /* RCU's kthread states for tracing. */
> >
> >
> 
> Good point. Paul, do you prefer to fold these changes into my patch or
> do we add a new one? In any case Li we need your Signed-off-by tag.

A separate patch works fine here because there should be no complaints
from compilers or tests about these.  Zhong, please do send with your
Signed-off-by, and I will queue them.

							Thanx, Paul

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