In message: <20051014091004.GC18513_at_uk.tiscali.com> Brian Candler <B.Candler_at_pobox.com> writes: : On Thu, Oct 13, 2005 at 11:10:26AM -0700, Brooks Davis wrote: : > > I don't think you can measure one single interger (or 64bit) increase in face : > > of a operation that has to access backing store. Even if there is a : > > performance hit, you don't have to build your kernel with the option enabled. : > : > The one thing I'd be worried about here is that 64bit updates are : > expensive on 32bit machines if you want them to be atomic. Relative to : > backing store they probably still don't matter, but the might be : > noticable. : : I'd be grateful if you could clarify that point for me. Are you saying that : if I write : : long long foo; : ... : foo++; : : then the C compiler generates code for 'foo++' which is not thread-safe? : (And therefore I would have to protect it with a mutex or critical section) : : Or are you saying that the C compiler inserts its own code around foo++ to : turn it into a critical section, and therefore runs less efficiently than : you'd expect? You have to protect this thread-unsafe operation yourself. WarnerReceived on Fri Oct 14 2005 - 13:00:55 UTC
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