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

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Message-ID: <1392666096.18779.6810.camel@triegel.csb>
Date:	Mon, 17 Feb 2014 20:41:36 +0100
From:	Torvald Riegel <triegel@...hat.com>
To:	"Joseph S. Myers" <joseph@...esourcery.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Will Deacon <will.deacon@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
	David Howells <dhowells@...hat.com>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"gcc@....gnu.org" <gcc@....gnu.org>
Subject: Re: [RFC][PATCH 0/5] arch: atomic rework

On Mon, 2014-02-17 at 18:59 +0000, Joseph S. Myers wrote:
> On Sat, 15 Feb 2014, Torvald Riegel wrote:
> 
> > glibc is a counterexample that comes to mind, although it's a smaller
> > code base.  (It's currently not using C11 atomics, but transitioning
> > there makes sense, and some thing I want to get to eventually.)
> 
> glibc is using C11 atomics (GCC builtins rather than _Atomic / 
> <stdatomic.h>, but using __atomic_* with explicitly specified memory model 
> rather than the older __sync_*) on AArch64, plus in certain cases on ARM 
> and MIPS.

I think the major steps remaining is moving the other architectures
over, and rechecking concurrent code (e.g., for the code that I have
seen, it was either asm variants (eg, on x86), or built before C11; ARM
pthread_once was lacking memory_barriers (see "pthread_once unification"
patches I posted)).  We also need/should to move towards using
relaxed-MO atomic loads instead of plain loads.



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