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

From: Sebastien Dugue <[email-masked]>
Date: Fri, 25 Jul 2008 10:47:30 +0200

On Fri, 25 Jul 2008 18:40:21 +1000 Benjamin Herrenschmidt <[email-masked]> wrote:

> On Fri, 2008-07-25 at 10:36 +0200, Sebastien Dugue wrote:
> > On Fri, 25 Jul 2008 18:27:20 +1000 Benjamin Herrenschmidt <[email-masked]> 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.

  Agreed. Will look into this in the next few days.

  Thanks,

  Sebastien.