linux-kernel - Re: Memory-ordering recipes

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Message-ID: <20170921124531.6ufvoxi3vz2rshqs@hirez.programming.kicks-ass.net>
Date:   Thu, 21 Sep 2017 14:45:31 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     j.alglave@....ac.uk, luc.maranget@...ia.fr, parri.andrea@...il.com,
        stern@...land.harvard.edu, dhowells@...hat.com,
        will.deacon@....com, boqun.feng@...il.com, npiggin@...il.com,
        linux-kernel@...r.kernel.org
Subject: Re: Memory-ordering recipes

On Sun, Sep 17, 2017 at 04:05:09PM -0700, Paul E. McKenney wrote:

> So what litmus tests are needed?  Here is my initial set:
> 
> 1.	Release-acquire chains, AKA ISA2, Z6.2, LB, and 3.LB
> 
> 	Lots of variety here, can in some cases substitute:
> 	
> 	a.	READ_ONCE() for smp_load_acquire()
> 	b.	WRITE_ONCE() for smp_store_release()
> 	c.	Dependencies for both smp_load_acquire() and
> 		smp_store_release().
> 	d.	smp_wmb() for smp_store_release() in first thread
> 		of ISA2 and Z6.2.
> 	e.	smp_rmb() for smp_load_acquire() in last thread of ISA2.
> 
> 2.	MP (see test6.pdf for nickname translation)
> 
> 	a.	smp_store_release() / smp_load_acquire()
> 	b.	rcu_assign_pointer() / rcu_dereference()
> 	c.	smp_wmb() / smp_rmb()
> 	d.	Replacing either of the above with smp_mb()
> 
> 3.	SB
> 
> 	a.	smp_mb(), as in lockless wait-wakeup coordination.
> 		And as in sys_membarrier()-scheduler coordination,
> 		for that matter.
> 
> Others?

So I have no idea what you're proposing here. The above is just a bunch
of words without meaning :-(