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Date:   Tue, 26 Jun 2018 21:27:28 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc:     linux-kernel@vger.kernel.org, mingo@kernel.org,
        jiangshanlai@gmail.com, dipankar@in.ibm.com,
        akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
        josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org,
        dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com,
        oleg@redhat.com, joel@joelfernandes.org
Subject: Re: [PATCH tip/core/rcu 16/27] rcu: Add comment documenting how
 rcu_seq_snap works
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On Tue, Jun 26, 2018 at 11:10:25AM -0700, Paul E. McKenney wrote:
> > Is the below not much simpler:
> > 
> > >  static inline unsigned long rcu_seq_snap(unsigned long *sp)
> > >  {
> > >  	unsigned long s;
> > 
> > 	s = smp_load_aquire(sp);
> > 
> > 	/* Add one GP */
> > 	s += 1 << RCU_SEQ_CTR_SHIFT;
> > 
> > 	/* Complete any pending state by rounding up */
> > 	s = __ALIGN_MASK(s, RCU_SEQ_STATE_MASK);
> > 
> > 	return s;
> > }
> 
> Seems equivalent to me, but with more lines.  To say nothing of more
> levels of lookup of macro definitions.  ;-)

But it does explain the various parts in the equation, or at least gives
a fair clue as to how the thing composes. And I find the alignment thing
far easier to read that an open coded variant, but whatever.