linux-kernel - Re: [RFC][PATCH 0/5] arch: atomic rework

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Message-ID: <20140218171746.GQ4250@linux.vnet.ibm.com>
Date:	Tue, 18 Feb 2014 09:17:46 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Mark Batty <Mark.Batty@...cam.ac.uk>
Cc:	Peter Sewell <Peter.Sewell@...cam.ac.uk>, peterz@...radead.org,
	Torvald Riegel <triegel@...hat.com>,
	torvalds@...ux-foundation.org, Will Deacon <will.deacon@....com>,
	Ramana.Radhakrishnan@....com, dhowells@...hat.com,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, mingo@...nel.org, gcc@....gnu.org
Subject: Re: [RFC][PATCH 0/5] arch: atomic rework

On Tue, Feb 18, 2014 at 03:16:33PM +0000, Mark Batty wrote:
> Hi Paul,
> 
> Thanks for the document. I'm looking forward to reading the bits about
> dependency chains in Linux.

And I am looking forward to your thoughts on those bits!

> > One point of confusion for me...  Example 4 says "language must allow".
> > Shouldn't that be "language is permitted to allow"?
> 
> When we say "allow", we mean that the optimised execution should be
> allowed by the specification, and Implicitly, the unoptimised
> execution should remain allowed too. We want to be concrete about what
> the language specification allows, and that's why we say "must". It is
> not to disallow the unoptimised execution.

OK, got it!

							Thanx, Paul

> > Seems like an
> > implementation is always within its rights to avoid an optimization if
> > its implementation prevents it from safely detecting the oppportunity
> > for that optimization.
> 
> That's right.
> 
> - Mark
> 
> 
> > Or am I missing something here?
> >
> >                                                         Thanx, Paul
> >
> 

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