On Mon, Oct 12, 2015 at 09:09:24PM +0800, Boqun Feng wrote: > On Mon, Oct 12, 2015 at 01:54:38PM +0200, Peter Zijlstra wrote: > > On Mon, Oct 12, 2015 at 05:06:36PM +0800, Boqun Feng wrote: > > > Understood. > > > > > > But, IMO, the position of this section is already misleading: > > > > > > (*) Implicit kernel memory barriers. > > > - Locking functions. > > > - Interrupt disabling functions. > > > ->- Sleep and wake-up functions.<- > > > - Miscellaneous functions. > > > > > > I read it as that sleep and wake-up functions provide some kernel memory > > > barriers which we can use *externally*(outside sleep/wakeup themselves). > > > > I think it is useful to state that the primitives handle the ordering > > between the waker and wakee wrt the 'blocking' state. > > > > I agree that's useful, however, the 'blocking' state is something > internal for sleep and wakeup, right? Not entirely; its also the @cond thing in wait queues. IE: for (;;) set_current_state(TASK_INTERRUPTIBLE); if (@cond) break; schedule(); } __set_current_state(TASK_RUNNING); vs. @cond = true; wake_up_process(p); So we guarantee that 'p' will see the @cond stores IF it does the wakeup. (If it does not, ie. 'p' wasn't sleeping, any guarantee is out the window). > Not sure whether the users of > wake_up() and wait_event() will care much about this or they need to > understand that detailedly to use wake_up() and wait_event() correctly. I think its mostly natural; but it explains why you don't have to do: wait_event(wq, @cond); vs. @cond = true; smp_wmb(); wake_up(wq); (or worse...) > > But I've not put much thought into wording. I wanted to finish process > > order 'comment' patch first. > > Of course. Actually your 'comment' patch is the reason why I think this > section may be removed. Yes, that is another option, referring to the comment, once that's sorted. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
