linux-kernel - Re: 3.0-git15 Atomic scheduling in pidmap

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Message-ID: <20110824235702.GC2417@linux.vnet.ibm.com>
Date:	Wed, 24 Aug 2011 16:57:02 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Josh Boyer <jwboyer@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: 3.0-git15 Atomic scheduling in pidmap_init

On Thu, Aug 25, 2011 at 01:34:24AM +0200, Frederic Weisbecker wrote:
> On Wed, Aug 24, 2011 at 04:12:55PM -0700, Paul E. McKenney wrote:
> > Indeed, this was a bogus patch.  The version I posted on the -rcu git
> > tree a few days ago has the correct "rdp->qs_pending = 0".  I thought
> > that I had chased down all the bogus copies, but obviously not.  :-(
> 
> Ah ok.
> 
> > > Should it perhaps set it to 1 only if we have rnp->gpnum > rnp->completed ?
> > 
> > I would rather keep it simple.  If rnp->gpnum > rnp->completed, then
> > the newly onlined CPU will notice and adjust appropriately soon enough.
> 
> Ah, just to ensure I understood well is that because rcu_pending() (called
> from tick) would detect rnp->gpnum != rdp->gpnum and thus trigger the softirq
> that notes the new gpnum and toggles  qs_pending?

Yep, that is the theory, anyway.  ;-)

							Thanx, Paul

> > > >  			rdp->passed_quiesc_completed = rnp->completed - 1;
> > > >  		}
> > > >  		raw_spin_unlock(&rnp->lock); /* irqs already disabled. */
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