Hi 2013/1/3 Oleg Nesterov <oleg@xxxxxxxxxx>: >> I want to ask you 'scheduler' people for your opinion: >> >> Maybe you remember my previous patch where I suggested an extra >> 'waitqueue empty' check before entering the critical section of the >> wakeup() function (If you do not remember see >> https://lkml.org/lkml/2012/10/25/159) >> >> Finally Oleg responded that a lot of callers do >> >> if (waitqueue_active(q)) >> wake_up(...); >> >> what made my patch pointless and adds a memory barrier. > > Plus this change doesn't look 100% correct, at least in theory. > >> I then decided >> to also implement the 'waitqueue_active' approach for my problem. > > Well, if you ask me I think this is the best solution ;) > > But I won't insist. > >> But now I get a review comment by Jiri that he would like to hide this >> 'if active behavior' in a wake_up_if_active() kind of function. I >> think he is right that implementing this check in the wakeup function >> would clean things up, right? >> >> I would like to have your opinion on the following two suggestions: >> - We still can do the original patch on the wake_up() that I >> suggested. I then can do an additional code cleanup patch that removes >> the double 'waitqueue_active' call (a quick grep found about 150 of >> these waitqueue active calls) on several places in the code. > > In this case we should also fix some users of add_wait_queue(). > >> - Or - as an alternative - I could add extra _if_active() versions of >> all wake_up() functions, that implement this extra test. > > Not sure this will actually help to make the code cleaner. The last > patch you sent looks simple and clean. IMHO it doesn't make sense > to create _if_active helper for each wake_up*. > > Oleg. > The comments by Oleg point out to me that the 'if waitqueueu_active' is a common practice for checking a waitqueue to be non empty. It is applied this way on several places in the kernel code. @Jiri, Alan, Greg: Don't you agree my patch makes sense? It solves an issue for me, and I really would like this patch to be approved. Regards, Ivo Sieben -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
