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

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Message-ID: <20131009145614.GA20828@localhost.localdomain>
Date:	Wed, 9 Oct 2013 16:56:19 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Thoughts on this RCU idle entry/exit patch?

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!
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