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Date: Fri, 17 Aug 2007 07:59:02 +0800 From: Herbert Xu <herbert@...dor.apana.org.au> To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Cc: Stefan Richter <stefanr@...6.in-berlin.de>, Paul Mackerras <paulus@...ba.org>, Satyam Sharma <satyam@...radead.org>, Christoph Lameter <clameter@....com>, Chris Snook <csnook@...hat.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-arch@...r.kernel.org, Linus Torvalds <torvalds@...ux-foundation.org>, netdev@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, ak@...e.de, heiko.carstens@...ibm.com, davem@...emloft.net, schwidefsky@...ibm.com, wensong@...ux-vs.org, horms@...ge.net.au, wjiang@...ilience.com, cfriesen@...tel.com, zlynx@....org, rpjday@...dspring.com, jesper.juhl@...il.com, segher@...nel.crashing.org Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures On Thu, Aug 16, 2007 at 09:34:41AM -0700, Paul E. McKenney wrote: > > The compiler can also reorder non-volatile accesses. For an example > patch that cares about this, please see: > > http://lkml.org/lkml/2007/8/7/280 > > This patch uses an ORDERED_WRT_IRQ() in rcu_read_lock() and > rcu_read_unlock() to ensure that accesses aren't reordered with respect > to interrupt handlers and NMIs/SMIs running on that same CPU. Good, finally we have some code to discuss (even though it's not actually in the kernel yet). First of all, I think this illustrates that what you want here has nothing to do with atomic ops. The ORDERED_WRT_IRQ macro occurs a lot more times in your patch than atomic reads/sets. So *assuming* that it was necessary at all, then having an ordered variant of the atomic_read/atomic_set ops could do just as well. However, I still don't know which atomic_read/atomic_set in your patch would be broken if there were no volatile. Could you please point them out? Cheers, -- Visit Openswan at http://www.openswan.org/ Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt - 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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