On Wed, Apr 11, 2018 at 10:46:28AM +0800, Yubin Ruan wrote: > On Tue, Apr 10, 2018 at 10:04:09AM -0700, Paul E. McKenney wrote: > > On Tue, Apr 10, 2018 at 11:20:24PM +0800, Yubin Ruan wrote: > > > On Tue, Apr 10, 2018 at 08:14:08PM +0800, Yubin Ruan wrote: > [...] > > > > > > > > Can you please provide me with some examples or references for different kinds > > > > of memory reordering in a SMP system? You know, there are different kinds of > > > > reordering: > > > > > > > > - Loads reordered after loads > > > > - Loads reordered after stores > > > > - Stores reordered after stores > > > > - Stores reordered after loads > > > > - Atomic reordered with loads > > > > - Atomic reordered with stores > > > > - Dependent loads reordered (DEC alpha) > > > > > > I remember there is open-std.org webpage containing comparision of C++'s > > > memory model to those primitives used in the Linux kernel. But I just can't > > > find that page. > > > > Here you go! > > > > http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0124r4.html > > > > There will be an update in a month or so, but the above is pretty > > close. Also, the Linux-kernel memory model was presented at > > ASPLOS and accepted into the Linux kernel itself: > > > > https://paulmck.livejournal.com/49667.html > > Many thanks. But I am currently confused about the relationship between > terminologies used in the Linux kernel and those used in some programming > languages (e.g., C++), i.e., the relationships between > > memory_order_release > memory_order_relaxed > memory_order_acquire > memory_order_seq_cst > ... > > and those used in the kernel: > > READ_ONCE() / WRITE_ONCE() > rmb() / wmb() / mb() / smp_mb() > ... > > Any materials for that? Hmm, to be more exact, what I want is something like this: “These primitives can be expressed directly in terms of the upcoming C++0x standard. For the smp_mb() primitive this correspondence is not exact; our memory barriers are somewhat stronger than the standard’s atomic_thread_fence(memory_order_seq_cst). The LOAD_SHARED() primitive maps to x.load(memory_order_relaxed) and STORE_SHARED() to x.store(memory_order_relaxed). The barrier() primitive maps to atomic_signal_fence(memory_order_seq_cst). In addition, rcu_dereference() maps to x.load(memory_order_consume) and rcu_assign_pointer() maps to x.store(v, memory_order_release).” This is extracted from the paper "User-Level Implementations of Read-Copy Update" by M. Desnoyers and P. McKenney, A. S. Stern, M. R. Dagenais and J. Walpole[1]. And the LOAD_SHARED() and STORE_SHARED() above are READ_ONCE() and WRITE_ONCE(), respectively. (BTW, LOAD_SHARED/STORE_SHARED seem to be better names than READ_ONCE/WRITE_ONCE, which are a bit confusing. How come people adopted those name?) (I find this after digging into a whole bunch of emails...hmm..email is a good thing) [1]: https://www.efficios.com/pub/rcu/urcu-main-accepted.pdf Yubin -- To unsubscribe from this list: send the line "unsubscribe perfbook" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
