Re: [PATCH tip/core/rcu 1/1] Tiny RCU changes for 3.9

[Paul E. McKenney]

On Mon, Jan 07, 2013 at 08:22:50PM -0800, Josh Triplett wrote:
> On Mon, Jan 07, 2013 at 02:19:15PM -0800, Paul E. McKenney wrote:
> > On Mon, Jan 07, 2013 at 09:56:06AM -0800, Josh Triplett wrote:
> > > On Mon, Jan 07, 2013 at 08:57:48AM -0800, Paul E. McKenney wrote:
> > > > On Mon, Jan 07, 2013 at 07:58:10AM -0800, Josh Triplett wrote:
> > > > > This patch seems reasonable to me, but the repeated use of #if
> > > > > defined(CONFIG_SMP) || defined(CONFIG_RCU_TRACE) seems somewhat
> > > > > annoying, and fragile if you ever decide to change the conditions.  How
> > > > > about defining an appropriate symbol in Kconfig for stall warnings, and
> > > > > using that?
> > > > 
> > > > But I only just removed the config option for SMP RCU stall warnings.  ;-)
> > > > 
> > > > But I must agree that "defined(CONFIG_SMP) || defined(CONFIG_RCU_TRACE)"
> > > > is a bit obscure.  The rationale is that RCU stall warnings are
> > > > unconditionally enabled in SMP kernels, but don't want to be in
> > > > TINY_RCU kernels due to size constraints.  I therefore put it under
> > > > CONFIG_RCU_TRACE, which also contains other TINY_RCU debugging-style
> > > > options.  Would adding a comment to this effect help?
> > > 
> > > I understand the rationale; I just think it would become clearer if you
> > > added an internal-only Kconfig symbol selected in both cases and change
> > > the conditionals to use that.
> > 
> > My concern was that this would confuse people into thinking that the
> > code under those #ifdefs was all the stall-warning code that there was.
> > 
> > I suppose this could be forestalled with a suitably clever name...
> > CONFIG_RCU_CPU_STALL_TINY_TOO?  Better names?
> 
> How about CONFIG_RCU_STALL_COMMON, with associated help text saying
> "include the stall-detection code common to both rcutree and rcutiny"?

Sold!!!  Especially given that I am creating the commit to allow
TREE_PREEMPT_RCU to be used on UP systems with an eye towards getting
rid of TINY_PREEMPT_RCU.  ;-)

							Thanx, Paul

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