On Wed, 2006-03-01 at 08:55 +0100, Arjan van de Ven wrote: > > then the question is when we should use which way? thanks! > > > set_bit() and friends are "smp safe", that is, if multiple cpus access > the same memory location (doesn't ahve to be the same bit) at the same > time, it's safe. > > bitfields do not provide that safety, if cpu 0 is writing bit 0, and cpu > 1 is writing bit 4 of a memory location, a really big mess will happen. > > > The flipside of that is that the "smp safe" comes with a price; it needs > atomic operations on the cpu level, and those are really expensive. > > So maybe a rule of thumb: > If you can guarantee that there will be no parallel accesses (due to > spinlocks or due to how your code works), use bitfields. If you need > your code to be SMP safe on itself, use set_bit() and co. If you fall in > either, think again, because you do you just don't know it yet ;) thanks! i like this rule. one more question, for bit field, if we use long xyz:n, will that be an issue in 32/64bit arch? i feel no, just to make sure. ming -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
