linux-kernel - Re: Compilers and RCU readers: Once more unto the breach!

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Message-ID: <20150522131252.GG6776@linux.vnet.ibm.com>
Date:	Fri, 22 May 2015 06:12:52 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Will Deacon <will.deacon@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"c++std-parallel@...u.org" <c++std-parallel@...u.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"gcc@....gnu.org" <gcc@....gnu.org>,
	p796231 <Peter.Sewell@...cam.ac.uk>,
	"mark.batty@...cam.ac.uk" <Mark.Batty@...cam.ac.uk>,
	Peter Zijlstra <peterz@...radead.org>,
	Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
	David Howells <dhowells@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"michaelw@...ibm.com" <michaelw@...ibm.com>
Subject: Re: Compilers and RCU readers: Once more unto the breach!

On Fri, May 22, 2015 at 08:43:44AM +0200, Ingo Molnar wrote:
> 
> * Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> >  (a) the "official" rules are completely pointless, and make sense 
> > only because the standard is written for some random "abstract 
> > machine" that doesn't actually exist.
> 
> Presuming the intent of the abstract machine specification is to avoid 
> being seen as biased towards any specific machine (politics), maybe 
> write this as:
> 
>    (a) the "official" rules are written for a somewhat weird and 
>        complex "union of all known and theoretically possible CPU 
>        architectures that exist or which might exist in the future", 
>        which machine does not actually exist in practice, but which 
>        allows a single abstract set of rules to apply to all machines. 
>        These rules are complex, but if applied to a specific machine 
>        they become considerably simpler. Here's a few examples: ...
> 
> ?
> 
> (Assuming it's a goal of this standard to be human parseable to more 
> than a few dozen people on the planet.)

Should something based on Section 7.9 go in, then I would need to add
a more developer-friendly explanation in Documentation/RCU, no two
ways about it!  ;-)

							Thanx, Paul

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