Messages in this thread | | | Date | Mon, 20 Aug 2007 09:28:05 -0400 | From | Chris Snook <> | Subject | Re: LDD3 pitfalls (was Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures) |
| |
Stefan Richter wrote: > Nick Piggin wrote: >> Stefan Richter wrote: >>> Nick Piggin wrote: >>> >>>> I don't know why people would assume volatile of atomics. AFAIK, most >>>> of the documentation is pretty clear that all the atomic stuff can be >>>> reordered etc. except for those that modify and return a value. >>> >>> Which documentation is there? >> Documentation/atomic_ops.txt >> >> >>> For driver authors, there is LDD3. It doesn't specifically cover >>> effects of optimization on accesses to atomic_t. >>> >>> For architecture port authors, there is Documentation/atomic_ops.txt. >>> Driver authors also can learn something from that document, as it >>> indirectly documents the atomic_t and bitops APIs. >>> >> "Semantics and Behavior of Atomic and Bitmask Operations" is >> pretty direct :) >> >> Sure, it says that it's for arch maintainers, but there is no >> reason why users can't make use of it. > > > Note, LDD3 page 238 says: "It is worth noting that most of the other > kernel primitives dealing with synchronization, such as spinlock and > atomic_t operations, also function as memory barriers." > > I don't know about Linux 2.6.10 against which LDD3 was written, but > currently only _some_ atomic_t operations function as memory barriers. > > Besides, judging from some posts in this thread, saying that atomic_t > operations dealt with synchronization may not be entirely precise.
atomic_t is often used as the basis for implementing more sophisticated synchronization mechanisms, such as rwlocks. Whether or not they are designed for that purpose, the atomic_* operations are de facto synchronization primitives.
-- Chris - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |