linux-kernel - Re: [PATCH RFC] Priority boosting for preemptible RCU

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Message-ID: <20070824172759.GC8589@linux.vnet.ibm.com>
Date:	Fri, 24 Aug 2007 10:27:59 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Gautham R Shenoy <ego@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	mingo@...e.hu, akpm@...ux-foundation.org, dipankar@...ibm.com,
	josht@...ux.vnet.ibm.com, tytso@...ibm.com, dvhltc@...ibm.com,
	tglx@...utronix.de
Subject: Re: [PATCH RFC] Priority boosting for preemptible RCU

On Fri, Aug 24, 2007 at 01:51:21PM +0530, Gautham R Shenoy wrote:
> On Thu, Aug 23, 2007 at 08:55:26AM -0700, Paul E. McKenney wrote:
> > > Even if we use another cpumask_t, whenever a cpu goes down or comes up,
> > > that will be reflected in this map, no? So what's the additional
> > > advantage of using it?
> > 
> > The additional map allows the code to use something other than the
> > lock_cpu_hotplug/unlock_cpu_hotplug, and also is robust against any
> > changes to the hotplug synchronization mechanism.  Might well be
> > better just to use the current hotplug synchronization mechanism,
> > but I was feeling paranoid.  ;-)
> 
> If it was doing something more complicated in the critical section other
> than summing stuff up, I would probably recommend going for another map
> instead of using the current hotplug synchronization. But for this case
> the current hotplug synchronization would work just fine.
> 
> I can very well understand your paranoia, but let me assure you, you are
> not the only one ;-)

OK, will try to keep an open mind...  ;-)

							Thanx, Paul
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