Hello Torvald, It looks like Paul clarified most of the points I was trying to make (thanks Paul!), so I won't go back over them here. On Thu, Feb 06, 2014 at 09:09:25PM +0000, Torvald Riegel wrote: > Are you familiar with the formalization of the C11/C++11 model by Batty > et al.? > http://www.cl.cam.ac.uk/~mjb220/popl085ap-sewell.pdf > http://www.cl.cam.ac.uk/~mjb220/n3132.pdf > > They also have a nice tool that can run condensed examples and show you > all allowed (and forbidden) executions (it runs in the browser, so is > slow for larger examples), including nice annotated graphs for those: > http://svr-pes20-cppmem.cl.cam.ac.uk/cppmem/ Thanks for the link, that's incredibly helpful. I've used ppcmem and armmem in the past, but I didn't realise they have a version for C++11 too. Actually, the armmem backend doesn't implement our atomic instructions or the acquire/release accessors, so it's not been as useful as it could be. I should probably try to learn OCaml... > IMHO, one thing worth considering is that for C/C++, the C11/C++11 is > the only memory model that has widespread support. So, even though it's > a fairly weak memory model (unless you go for the "only seq-cst" > beginners advice) and thus comes with a higher complexity, this model is > what likely most people will be familiar with over time. Deviating from > the "standard" model can have valid reasons, but it also has a cost in > that new contributors are more likely to be familiar with the "standard" > model. Indeed, I wasn't trying to write-off the C11 memory model as something we can never use in the kernel. I just don't think the current situation is anywhere close to usable for a project such as Linux. If a greater understanding of the memory model does eventually manifest amongst C/C++ developers (by which I mean, the beginners advice is really treated as such and there is a widespread intuition about ordering guarantees, as opposed to the need to use formal tools), then surely the tools and libraries will stabilise and provide uniform semantics across the 25+ architectures that Linux currently supports. If *that* happens, this discussion is certainly worth having again. Will -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
