linux-kernel - Re: [PATCH 2/2][RT] powerpc - Make the irq reverse mapping radix tree lockless

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Message-Id: <1216975221.11188.102.camel@pasglop>
Date:	Fri, 25 Jul 2008 18:40:21 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Sebastien Dugue <sebastien.dugue@...l.net>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Linux-rt <linux-rt-users@...r.kernel.org>,
	linux-ppc <linuxppc-dev@...abs.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <michael@...erman.id.au>,
	Tim Chavez <tinytim@...ibm.com>,
	Jean Pierre Dion <jean-pierre.dion@...l.net>,
	Gilles Carry <Gilles.Carry@....bull.net>
Subject: Re: [PATCH 2/2][RT] powerpc - Make the irq reverse mapping radix
	tree lockless

On Fri, 2008-07-25 at 10:36 +0200, Sebastien Dugue wrote:
> On Fri, 25 Jul 2008 18:27:20 +1000 Benjamin Herrenschmidt <benh@...nel.crashing.org> wrote:
> 
> > On Fri, 2008-07-25 at 09:49 +0200, Peter Zijlstra wrote:
> > > 
> > > 
> > > The only advantage of the concurrent radix tree over this model is that
> > > it can potentially do multiple modification operations at the same time.
> > 
> > Yup, we do not need that for the irq revmap... concurrent lookup is all we need.
> > 
> 
>   Shouldn't we care about concurrent insertion and deletion in the tree? I agree
> that concern might be a bit artificial but in theory that can happen.

Yes, we just need to protect it with a big hammer, like a spinlock, it's
not a performance critical code path.

Ben.


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