linux-kernel - Re: Thoughts on this RCU idle entry/exit patch?

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Message-ID: <20131009150829.GW5790@linux.vnet.ibm.com>
Date:	Wed, 9 Oct 2013 08:08:29 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Thoughts on this RCU idle entry/exit patch?

On Wed, Oct 09, 2013 at 04:56:19PM +0200, Frederic Weisbecker wrote:
> On Tue, Oct 08, 2013 at 02:12:18PM -0700, Paul E. McKenney wrote:
> > On Tue, Oct 08, 2013 at 10:34:28PM +0200, Frederic Weisbecker wrote:
> > > So I wonder, do we want to continue to allow this nesting? I remember that DYNTICK_TASK_NEST_*
> > > stuff is there to protects against non finishing interrupts on some archs (I also remember that
> > > this, or at least a practical scenario for this, was hard to really define though :o)
> > > But then wouldn't it involve other kind of scenario like this?
> > > 
> > >        rcu_irq_enter()
> > >            rcu_eqs_enter()
> > >            rcu_eqs_exit()
> > >            ...
> > > 
> > > Anyway, that's just random thougths on further simplifications, in any case, this
> > > patch looks good.
> > 
> > Yep, if no task-level nesting is ever required, things could be a bit
> > simpler.  I would be a bit slow about making such a change, though.
> > After all, the need to deal with Hotel California interrupts means that
> > handling nesting isn't that big of a deal comparatively.  ;-)
> 
> Right, well ideally it would be even best to fix the corner case(s) if there aren't
> that many of them. I mean calling rcu_irq_exit() from the end of those half interrupts
> I guess. It would make it much simpler than this complicated nesting handled on the core code.
> But I agree there is a bit of unknown out there, so yeah lets be prudent :)
> 
> > May I add your Reviewed-by?
> 
> Sure, thanks!

Done!

							Thanx, Paul

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