On Wed, May 14, 2025 at 10:43:12AM +0200, Gabriele Monaco wrote:
> -static inline void
> \
> -da_monitor_set_state_##name(struct da_monitor *da_mon, enum states_##name
> state) \
> +static inline bool
> \
> +da_monitor_set_state_##name(struct da_monitor *da_mon, enum states_##name
> prev_state, \
> + enum states_##name state)
> \
> {
> \
> - da_mon->curr_state = state;
> \
> + return try_cmpxchg(&da_mon->curr_state, &prev_state, state);
> \
> }
> \
This is a very thin wrapper. Should we just call try_cmpxchg() directly?
> static inline bool
> \
> da_event_##name(struct da_monitor *da_mon, enum events_##name event)
> \
> {
> \
> - type curr_state = da_monitor_curr_state_##name(da_mon);
> \
> - type next_state = model_get_next_state_##name(curr_state, event);
> \
> + bool changed;
> \
> + type curr_state, next_state;
> \
>
> \
> - if (next_state != INVALID_STATE) {
> \
> - da_monitor_set_state_##name(da_mon, next_state);
> \
> + for (int i = 0; i < MAX_DA_RETRY_RACING_EVENTS; i++) {
> \
> + curr_state = da_monitor_curr_state_##name(da_mon);
> \
For the follow-up iterations (i > 0), it is not necessary to read
curr_state again here, we already have its value from try_cmpxchg() below.
Also, thinking about memory barrier hurts my main, but I'm not entirely
sure if reading curr_state without memory barrier here is okay.
How about something like below?
curr_state = da_monitor_curr_state_##name(da_mon);
for (int i = 0; i < MAX_DA_RETRY_RACING_EVENTS; i++) {
next_state = model_get_next_state_##name(curr_state, event);
if (next_state == INVALID_STATE)
break;
if (try_cmpxchg(&da_mon->curr_state, &curr_state, next_state))
break;
}
Furthermore, it is possible to replace for(...) with while (1)? I don't
think we can have a live lock, because if we fail to do try_cmpxchg(),
the "other guy" surely succeed.
Best regards,
Nam
