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

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Message-ID: <555C8FBE.4020505@arm.com>
Date:	Wed, 20 May 2015 14:44:30 +0100
From:	Ramana Radhakrishnan <ramana.radhakrishnan@....com>
To:	David Howells <dhowells@...hat.com>,
	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>
CC:	Will Deacon <Will.Deacon@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	"michaelw@...ibm.com" <michaelw@...ibm.com>
Subject: Re: Compilers and RCU readers: Once more unto the breach!



On 20/05/15 14:37, David Howells wrote:
> Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
>
>> I was thinking of "y" as a simple variable, but if it is something more
>> complex, then the compiler could do this, right?
>>
>> 	char *x;
>>
>> 	y;
>> 	x = z;
>
> Yeah.  I presume it has to maintain the ordering, though.

The scheduler for e.g. is free to reorder if it can prove there is no 
dependence (or indeed side-effects for y) between insns produced for y 
and `x = z'.

regards
Ramana

>
> David
>
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