On Fri, Sep 29, 2017 at 02:17:32AM +0200, Jens Axboe wrote: > On 09/28/2017 11:44 PM, Linus Torvalds wrote: > > On Thu, Sep 28, 2017 at 2:41 PM, Andrew Morton > > <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > >> > >> test_and_set_bit()? > > > > If there aren't any atomicity concerns (either because of higher-level > > locking, or because racing and having two people set the bit is fine), > > it can be better to do them separately if the test_bit() is the common > > case and you can avoid dirtying a cacheline that way. > > > > But yeah, if that is the case, it might be worth documenting, because > > test_and_set_bit() is the more obviously appropriate "there can be > > only one" model. > > It is documented though, but maybe not well enough... > > I've actually had to document/explain it enough times now, that it > might be worth making a general construct. Though it has to be > used carefully, so perhaps it's better contained as separate use > cases. test_and_test_and_set_bit()? It's an unusual name, so when either reading it or writing it, people are going to say "something unusual here", rather than "That Jens Axboe is such a n00b, he doesn't know how to use test_and_set_bit()". There are a few references out on the web to test-and-test-and-set already, so it's not entirely unique to Linux. Plus, some architectures might be able to optimise that, particularly those which are ll/sc based. It might be exactly the same as their test_and_set().
