> > -A write memory barrier is implied by wake_up() and co. if and only if they > > -wake something up. The barrier occurs before the task state is cleared, and so > > -sits between the STORE to indicate the event and the STORE to set TASK_RUNNING: > > +A general memory barrier is executed by wake_up() if it wakes something up. > > +If it doesn't wake anything up then a memory barrier may or may not be > > +executed; you must not rely on it. The barrier occurs before the task state > > +is accessed, in part., it sits between the STORE to indicate the event and > > +the STORE to set TASK_RUNNING: > > Minor suggestion: Instead of "in part.", how about "that is"? > > (I generally find "in part." to be at least a little confusing, > probably because "part" is itself a word and "in part" is a > reasonably common phrase in English.) Mmh, the fact is that that "before the task state is accessed" does want to include the LOAD from ->state to check for the task state (recall the pattern in [1])...; how about if I expand "in part." to "in particular"? > > > > > - CPU 1 CPU 2 > > + CPU 1 (Sleeper) CPU 2 (Waker) > > =============================== =============================== > > set_current_state(); STORE event_indicated > > smp_store_mb(); wake_up(); > > - STORE current->state <write barrier> > > - <general barrier> STORE current->state > > - LOAD event_indicated > > + STORE current->state ... > > + <general barrier> <general barrier> > > + LOAD event_indicated if ((LOAD task->state) & TASK_NORMAL) > > + STORE task->state > > > > -To repeat, this write memory barrier is present if and only if something > > -is actually awakened. To see this, consider the following sequence of > > -events, where X and Y are both initially zero: > > +where "task" is the thread being woken up and it equals CPU 1's current. > > Since "task" is in quotation marks, "current" should also be in > quotation marks. Sure, will fix in v2. Thanks, Andrea > > Alan > -- 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
