On Tue, Oct 25, 2016 at 03:30:54PM -0700, Dmitry Torokhov wrote: > Hi, > > Reading Documentation/scheduler/completion.txt, complete_all() is
Oh, there is documentation? /me goes read. > supposed to be usable with "forever" completions, i.e. when we have an > action that happens once and stays "done" for the rest of lifetime of an > object, no matter how many times we check for "doneness". I suppose you allude to this wording: "calls complete_all() to signal all current and future waiters." > However the > implementation for complete_all() simply sets the counter to be greater > or equal UINT_MAX/2 and do_wait_for_common() happily decreases it on > every call. This is indeed so. > Is it simply an artefact of [older] implementation where we do not > expect to make that many calls to wait_for_completion*() so that > completion that is signalled with ocmplete_all() is practically stays > signalled forever? The text says it was written against v3.18 or thereabout, and that implementation looks a lot like todays, so I doubt it ever worked like that. > Or do we need something like this in > do_wait_for_common(): > > if (x->done < UINT_MAX/2) > x->done--; Depends a bit, do you really want this? Seems a bit daft to keep asking if its done already, seems like a waste of cycles to me.