linux-kernel - Re: [PATCH RFC tip/core/rcu 05/14] rcu: Abstract sequence counting from synchronize_sched

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Message-ID: <20150702165032.GC19282@twins.programming.kicks-ass.net>
Date:	Thu, 2 Jul 2015 18:50:32 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org,
	dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH RFC tip/core/rcu 05/14] rcu: Abstract sequence counting
 from synchronize_sched_expedited()

On Thu, Jul 02, 2015 at 07:13:30AM -0700, Paul E. McKenney wrote:

> > Its really time for them to stop wanking and stare reality in the face.
> 
> Indeed, I have been and will be continuing to make myself unpopular with
> that topic.  ;-)

Thanks!!

> > > > > +/* Wrapper functions for expedited grace periods.  */
> > > > > +static void rcu_exp_gp_seq_start(struct rcu_state *rsp)
> > > > > +{
> > > > > +	rcu_seq_start(&rsp->expedited_sequence);
> > > > > +}
> > > > > +static void rcu_exp_gp_seq_end(struct rcu_state *rsp)
> > > > > +{
> > > > > +	rcu_seq_end(&rsp->expedited_sequence);
> > > > > +}
> > > > > +static unsigned long rcu_exp_gp_seq_snap(struct rcu_state *rsp)
> > > > > +{
> > > > > +	return rcu_seq_snap(&rsp->expedited_sequence);
> > > > > +}
> > > > > +static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s)
> > > > > +{
> > > > > +	return rcu_seq_done(&rsp->expedited_sequence, s);
> > > > > +}
> > > > 
> > > > This is wrappers for wrappers sake? Why?
> > > 
> > > For _rcu_barrier(), as noted in the commit log.
> > 
> > Yes it said; but why? Surely _rcu_barrier() can do the
> > ->expedited_sequence thing itself, that hardly seems worthy of a
> > wrapper.
> 
> Ah, you want synchronize_rcu_expedited() and synchronize_sched_expedited()
> to use rcu_seq_start() and friends directly.  I can certainly do that.

Well, 'want' is a strong word, I was just questioning the use of these
trivial wrappers.
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