On 10/04, Joel Fernandes (Google) wrote: > > But this is not always true if you consider the following events: I'm afraid I missed your point, but... > ----------------------> > GP num 111111 22222222222222222222222222222222233333333 > GP state i e p x r rx i > CPU0 : rse rsx > CPU1 : rse rsx > CPU2 : rse rsx > > Here, we had 3 grace periods that elapsed, 1 for the rcu_sync_enter(), > and 2 for the rcu_sync_exit(s). But this is fine? We only need to ensure that we have a full GP pass between the "last" rcu_sync_exit() and GP_XXX -> GP_IDLE transition. > However, we had 3 rcu_sync_exit()s, not 2. In other words, the > rcu_sync_exit() got batched. > > So my point here is, rcu_sync_exit() does not really always cause a new > GP to happen See above, it should not. > Then what is the point of the GP_REPLAY state at all if it does not > always wait for a new GP? Again, I don't understand... GP_REPLAY ensures that we will have a full GP before rcu_sync_func() sets GP_IDLE, note that it does another "recursive" call_rcu() if it sees GP_REPLAY. > Taking a step back, why did we intend to have > to wait for a new GP if another rcu_sync_exit() comes while one is still > in progress? To ensure that if another CPU sees rcu_sync_is_idle() (GP_IDLE) after you do rcu_sync_exit(), then it must also see all memory changes you did before rcu_sync_exit(). Oleg.
