linux-kernel - Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

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Message-ID: <20170712115451.xxz3jkau7ape76n5@hirez.programming.kicks-ass.net>
Date:   Wed, 12 Jul 2017 13:54:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Frederic Weisbecker <fweisbec@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        "Li, Aubrey" <aubrey.li@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Aubrey Li <aubrey.li@...el.com>, tglx@...utronix.de,
        len.brown@...el.com, rjw@...ysocki.net, tim.c.chen@...ux.intel.com,
        arjan@...ux.intel.com, yang.zhang.wz@...il.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

On Tue, Jul 11, 2017 at 11:09:31AM -0700, Paul E. McKenney wrote:
> On Tue, Jul 11, 2017 at 06:34:22PM +0200, Peter Zijlstra wrote:

> > But I think we can at the very least do this; it only gets called from
> > kernel/sched/idle.c and both callsites have IRQs explicitly disabled by
> > that point.
> > 
> > 
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 51d4c3acf32d..dccf2dc8155a 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -843,13 +843,8 @@ static void rcu_eqs_enter(bool user)
> >   */
> >  void rcu_idle_enter(void)
> >  {
> > -	unsigned long flags;
> > -
> > -	local_irq_save(flags);
> 
> With this addition, I am all for it:
> 
> RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_idle_enter() invoked with irqs enabled!!!");
> 
> If you are OK with this addition, may I please have your Signed-off-by?

Sure,

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

> 
> >  	rcu_eqs_enter(false);
> > -	local_irq_restore(flags);
> >  }
> > -EXPORT_SYMBOL_GPL(rcu_idle_enter);
> > 
> >  #ifdef CONFIG_NO_HZ_FULL
> >  /**
> > 
>