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Date: Fri, 17 Aug 2007 21:13:35 -0700 (PDT) From: Linus Torvalds <torvalds@...ux-foundation.org> To: Satyam Sharma <satyam@...radead.org> cc: Christoph Lameter <clameter@....com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Herbert Xu <herbert@...dor.apana.org.au>, 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, 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 Sat, 18 Aug 2007, Satyam Sharma wrote: > > No code does (or would do, or should do): > > x.counter++; > > on an "atomic_t x;" anyway. That's just an example of a general problem. No, you don't use "x.counter++". But you *do* use if (atomic_read(&x) <= 1) and loading into a register is stupid and pointless, when you could just do it as a regular memory-operand to the cmp instruction. And as far as the compiler is concerned, the problem is the 100% same: combining operations with the volatile memop. The fact is, a compiler that thinks that movl mem,reg cmpl $val,reg is any better than cmpl $val,mem is just not a very good compiler. But when talking about "volatile", that's exactly what ytou always get (and always have gotten - this is not a regression, and I doubt gcc is alone in this). Linus - 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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