linux-kernel - Re: [PATCH tip/core/rcu 01/23] rcu: Move RCU grace-period initialization into a kthread

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Message-ID: <20120906170047.GI2448@linux.vnet.ibm.com>
Date:	Thu, 6 Sep 2012 10:00:47 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, 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 01/23] rcu: Move RCU grace-period
 initialization into a kthread

On Thu, Sep 06, 2012 at 03:32:22PM +0200, Peter Zijlstra wrote:
> On Thu, 2012-08-30 at 11:18 -0700, Paul E. McKenney wrote:
> > +static int rcu_gp_kthread(void *arg)
> > +{
> > +       unsigned long flags;
> > +       struct rcu_data *rdp;
> > +       struct rcu_node *rnp;
> > +       struct rcu_state *rsp = arg;
> > +
> > +       for (;;) {
> > +
> > +               /* Handle grace-period start. */
> > +               rnp = rcu_get_root(rsp);
> > +               for (;;) {
> > +                       wait_event_interruptible(rsp->gp_wq, rsp->gp_flags);
> > +                       if (rsp->gp_flags)
> > +                               break;
> > +                       flush_signals(current);
> > +               }
> > +               raw_spin_lock_irqsave(&rnp->lock, flags); 
> 
> You're in a kthread, it should be impossible for IRQs to be disabled
> here, no? Similar for most (all) other sites in this function.
> 
> Using the unconditional IRQ disable/enable is generally faster.

I suppose I could see my way to using raw_spin_lock_irq() here.  ;-)

							Thanx, Paul

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