linux-kernel - Re: [PATCH RFC tip/core/rcu] rcu: direct algorithmic SRCU implementation

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Message-ID: <20120216111421.GA13497@Krystal>
Date:	Thu, 16 Feb 2012 06:14:21 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
	patches@...aro.org, Avi Kiviti <avi@...hat.com>,
	Chris Mason <chris.mason@...cle.com>,
	Eric Paris <eparis@...hat.com>
Subject: Re: [PATCH RFC tip/core/rcu] rcu: direct algorithmic SRCU
	implementation

* Peter Zijlstra (peterz@...radead.org) wrote:
> On Thu, 2012-02-16 at 05:50 -0500, Mathieu Desnoyers wrote:
> > > Ah, so something like this?
> > > 
> > >       ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) += 
> > >               SRCU_USAGE_COUNT + 1;
> > > 
> > > Now that you mention it, this does look nicer, applied here and to
> > > srcu_read_unlock().
> > 
> > I think Peter refers to __this_cpu_add(). 
> 
> I'm not sure that implies the ACCESS_ONCE() thing
> 

Fair point. The "generic" fallback for this_cpu_add does not imply the
ACCESS_ONCE() semantic AFAIK. I don't know if there would be a clean way
to get both without duplicating these operations needlessly.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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