On Wed, Aug 15, 2007 at 04:38:54AM +0530, Satyam Sharma wrote: > > > On Tue, 14 Aug 2007, Christoph Lameter wrote: > > > On Thu, 9 Aug 2007, Chris Snook wrote: > > > > > This patchset makes the behavior of atomic_read uniform by removing the > > > volatile keyword from all atomic_t and atomic64_t definitions that > > > currently > > > have it, and instead explicitly casts the variable as volatile in > > > atomic_read(). This leaves little room for creative optimization by the > > > compiler, and is in keeping with the principles behind "volatile > > > considered > > > harmful". > > > > volatile is generally harmful even in atomic_read(). Barriers control > > visibility and AFAICT things are fine. > > Frankly, I don't see the need for this series myself either. Personal > opinion (others may differ), but I consider "volatile" to be a sad / > unfortunate wart in C (numerous threads on this list and on the gcc > lists/bugzilla over the years stand testimony to this) and if we _can_ > steer clear of it, then why not -- why use this ill-defined primitive > whose implementation has often differed over compiler versions and > platforms? Granted, barrier() _is_ heavy-handed in that it makes the > optimizer forget _everything_, but then somebody did post a forget() > macro on this thread itself ... > > [ BTW, why do we want the compiler to not optimize atomic_read()'s in > the first place? Atomic ops guarantee atomicity, which has nothing > to do with "volatility" -- users that expect "volatility" from > atomic ops are the ones who must be fixed instead, IMHO. ]
Interactions between mainline code and interrupt/NMI handlers on the same CPU (for example, when both are using per-CPU variables. See examples previously posted in this thread, or look at the rcu_read_lock() and rcu_read_unlock() implementations in http://lkml.org/lkml/2007/8/7/280. Thanx, Paul - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
