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Date: Sat, 18 Aug 2007 14:56:52 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Christoph Lameter <clameter@....com> Cc: Herbert Xu <herbert@...dor.apana.org.au>, Linus Torvalds <torvalds@...ux-foundation.org>, Nick Piggin <nickpiggin@...oo.com.au>, Paul Mackerras <paulus@...ba.org>, Segher Boessenkool <segher@...nel.crashing.org>, heiko.carstens@...ibm.com, horms@...ge.net.au, linux-kernel@...r.kernel.org, rpjday@...dspring.com, ak@...e.de, netdev@...r.kernel.org, cfriesen@...tel.com, akpm@...ux-foundation.org, jesper.juhl@...il.com, linux-arch@...r.kernel.org, zlynx@....org, satyam@...radead.org, schwidefsky@...ibm.com, Chris Snook <csnook@...hat.com>, davem@...emloft.net, wensong@...ux-vs.org, wjiang@...ilience.com Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures On Fri, Aug 17, 2007 at 06:24:15PM -0700, Christoph Lameter wrote: > On Fri, 17 Aug 2007, Paul E. McKenney wrote: > > > On Sat, Aug 18, 2007 at 08:09:13AM +0800, Herbert Xu wrote: > > > On Fri, Aug 17, 2007 at 04:59:12PM -0700, Paul E. McKenney wrote: > > > > > > > > gcc bugzilla bug #33102, for whatever that ends up being worth. ;-) > > > > > > I had totally forgotten that I'd already filed that bug more > > > than six years ago until they just closed yours as a duplicate > > > of mine :) > > > > > > Good luck in getting it fixed! > > > > Well, just got done re-opening it for the third time. And a local > > gcc community member advised me not to give up too easily. But I > > must admit that I am impressed with the speed that it was identified > > as duplicate. > > > > Should be entertaining! ;-) > > Right. ROTFL... volatile actually breaks atomic_t instead of making it > safe. x++ becomes a register load, increment and a register store. Without > volatile we can increment the memory directly. It seems that volatile > requires that the variable is loaded into a register first and then > operated upon. Understandable when you think about volatile being used to > access memory mapped I/O registers where a RMW operation could be > problematic. > > See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3506 Yep. The initial reaction was in fact to close my bug as a duplicate of 3506. But I was not asking for atomicity, but rather for smaller code to be generated, so I reopened it. Thanx, Paul - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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