(I've cleaned To: and subject a bit :) Da Zheng, le Wed 23 Dec 2009 21:23:23 +0800, a écrit : > Samuel Thibault wrote: > >> Is there anything else we should worry about? > > Ordering. See /usr/src/linux/Documentation/memory-barriers.txt > It's a long file. There are a lot to study:)
Yes, it's very instructive. > >> Then the use of volatile is very limited and the only case I can think of > >> is something like signal handling where there is long jump. > > > > There's also memory-mapped hardware registers (for which the OS has to > > disable processor cache too, of course). > You mean memory-mapped IO? Yes. > Does it mean all machines have to provide at least one instruction > that can modify variables in memory direct? so we can implement > spin_lock or something similar. Yes. An architecture that wouldn't provide at least an atomic test and set would be a nightmare to program (just memory barriers is theorically enough, but it's a nightmare :) ) Samuel
