Messages in this thread | | | Date | Sun, 4 Feb 2024 23:32:07 +0100 | From | Frederic Weisbecker <> | Subject | Re: [PATCH v10 18/20] timers: Implement the hierarchical pull model |
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Le Mon, Jan 15, 2024 at 03:37:41PM +0100, Anna-Maria Behnsen a écrit : > +/* > + * Returns true, if there is nothing to be propagated to the next level > + * > + * @data->firstexp is set to expiry of first gobal event of the (top level of > + * the) hierarchy, but only when hierarchy is completely idle. > + * > + * This is the only place where the group event expiry value is set. > + */ > +static > +bool tmigr_update_events(struct tmigr_group *group, struct tmigr_group *child, > + struct tmigr_walk *data, union tmigr_state childstate, > + union tmigr_state groupstate) > +{ > + struct tmigr_event *evt, *first_childevt; > + bool walk_done, remote = data->remote; > + bool leftmost_change = false; > + u64 nextexp; > + > + if (child) { > + raw_spin_lock(&child->lock); > + raw_spin_lock_nested(&group->lock, SINGLE_DEPTH_NESTING); > + > + if (childstate.active) { > + walk_done = true; > + goto unlock; > + } > + > + first_childevt = tmigr_next_groupevt(child); > + nextexp = child->next_expiry; > + evt = &child->groupevt; > + } else { > + nextexp = data->nextexp; > + > + first_childevt = evt = data->evt; > + > + /* > + * Walking the hierarchy is required in any case when a > + * remote expiry was done before. This ensures to not lose > + * already queued events in non active groups (see section > + * "Required event and timerqueue update after a remote > + * expiry" in the documentation at the top). > + * > + * The two call sites which are executed without a remote expiry > + * before, are not prevented from propagating changes through > + * the hierarchy by the return: > + * - When entering this path by tmigr_new_timer(), @evt->ignore > + * is never set. > + * - tmigr_inactive_up() takes care of the propagation by > + * itself and ignores the return value. But an immediate > + * return is required because nothing has to be done in this > + * level as the event could be ignored. > + */ > + if (evt->ignore && !remote) > + return true; > + > + raw_spin_lock(&group->lock); > + } > + > + if (nextexp == KTIME_MAX) { > + evt->ignore = true; > + > + /* > + * When the next child event could be ignored (nextexp is > + * KTIME_MAX) and there was no remote timer handling before or > + * the group is already active, there is no need to walk the > + * hierarchy even if there is a parent group. > + * > + * The other way round: even if the event could be ignored, but > + * if a remote timer handling was executed before and the group > + * is not active, walking the hierarchy is required to not miss > + * an enqueued timer in the non active group. The enqueued timer > + * of the group needs to be propagated to a higher level to > + * ensure it is handled. > + */ > + if (!remote || groupstate.active) { > + walk_done = true; > + goto unlock;
So if the current tmc going inactive was the migrator for the whole hierarchy and it is reaching here the top-level, this assumes that if none of this tmc's groups have a timer, then it can just return. But what if the top level has timers from other children? Who is going to handle them then?
Should this be "goto check_toplvl" instead?
Thanks.
> + } > + } else { > + /* > + * An update of @evt->cpu and @evt->ignore flag is required only > + * when @child is set (the child is equal or higher than lvl0), > + * but it doesn't matter if it is written once more to the per > + * CPU event; make the update unconditional. > + */ > + evt->cpu = first_childevt->cpu; > + evt->ignore = false; > + } > + > + walk_done = !group->parent; > + > + /* > + * If the child event is already queued in the group, remove it from the > + * queue when the expiry time changed only. > + */ > + if (timerqueue_node_queued(&evt->nextevt)) { > + if (evt->nextevt.expires == nextexp) > + goto check_toplvl; > + > + leftmost_change = timerqueue_getnext(&group->events) == &evt->nextevt; > + if (!timerqueue_del(&group->events, &evt->nextevt)) > + WRITE_ONCE(group->next_expiry, KTIME_MAX); > + } > + > + evt->nextevt.expires = nextexp; > + > + if (timerqueue_add(&group->events, &evt->nextevt)) { > + leftmost_change = true; > + WRITE_ONCE(group->next_expiry, nextexp); > + } > + > +check_toplvl: > + if (walk_done && (groupstate.migrator == TMIGR_NONE)) { > + /* > + * Nothing to do when first event didn't changed and update was > + * done during remote timer handling. > + */ > + if (remote && !leftmost_change) > + goto unlock; > + /* > + * The top level group is idle and it has to be ensured the > + * global timers are handled in time. (This could be optimized > + * by keeping track of the last global scheduled event and only > + * arming it on the CPU if the new event is earlier. Not sure if > + * its worth the complexity.) > + */ > + data->firstexp = tmigr_next_groupevt_expires(group); > + } > + > +unlock: > + raw_spin_unlock(&group->lock); > + > + if (child) > + raw_spin_unlock(&child->lock); > + > + return walk_done; > +}
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