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eventq: change the event datastructure back to LIFO.

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The status quo is preferred since it is less likely that people will
rely on LIFO than FIFO, and when we move to a parallelized M5, no
ordering between events of the same time/priority will be guaranteed.
This commit is contained in:
Nathan Binkert 2008-07-11 08:48:50 -07:00
parent 10df68dd72
commit f90b08a5cc
2 changed files with 63 additions and 79 deletions
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136
src/sim/eventq.cc
View file

@ -57,29 +57,25 @@ EventQueue mainEventQueue("MainEventQueue");
Counter Event::instanceCounter = 0;
#endif
inline void
inline Event *
insertBefore(Event *event, Event *curr)
{
// Either way, event will be the last element in the 'in bin' list
// Either way, event will be the top element in the 'in bin' list
// which is the pointer we need in order to look into the list, so
// we need to insert that into the bin list.
if (!curr || *event < *curr) {
// Insert the event before the current list since it is in the future.
event->nextBin = curr;
// We need to create a new 'in bin' list
event->nextInBin = event;
event->nextInBin = NULL;
} else {
// Since we're on the correct list, we need to point to the next list
event->nextBin = curr->nextBin; // curr->nextBin can now become stale
// Insert event at the end of the 'nextInBin' curr is the last
// element on the 'in bin' list and curr->nextInBin is the first
event->nextInBin = curr->nextInBin; // event->nextInBin needs to
// point to the first
curr->nextInBin = event; // curr->nextInBin is now second to last
// Insert event at the top of the stack
event->nextInBin = curr;
}
return event;
}
void
@ -87,54 +83,53 @@ EventQueue::insert(Event *event)
{
// Deal with the head case
if (!head || *event <= *head) {
insertBefore(event, head);
head = event;
head = insertBefore(event, head);
return;
}
// Figure out either which 'in bin' list we are on, or where a new list
// needs to be inserted
Event *curr = head;
Event *next = head->nextBin;
while (next && *next < *event) {
curr = next;
next = next->nextBin;
Event *prev = head;
Event *curr = head->nextBin;
while (curr && *curr < *event) {
prev = curr;
curr = curr->nextBin;
}
insertBefore(event, next);
curr->nextBin = event; // all nextBin pointers on the curr
// 'in bin' list are now stale
// Note: this operation may render all nextBin pointers on the
// prev 'in bin' list stale (except for the top one)
prev->nextBin = insertBefore(event, curr);
}
inline Event *
removeItem(Event *event, Event *last)
removeItem(Event *event, Event *top)
{
Event *prev = last;
Event *curr = last->nextInBin;
Event *curr = top;
Event *next = top->nextInBin;
while (event != curr) {
if (curr == last)
panic("event not found!");
prev = curr;
curr = curr->nextInBin;
// if we removed the top item, we need to handle things specially
// and just remove the top item, fixing up the next bin pointer of
// the new top item
if (event == top) {
if (!next)
return top->nextBin;
next->nextBin = top->nextBin;
return next;
}
// If this was the only item in this list, we're done.
if (prev == curr)
return NULL;
// Since we already checked the current element, we're going to
// keep checking event against the next element.
while (event != next) {
if (!next)
panic("event not found!");
// remove curr from the 'in bin' list since it's what we're looking for
prev->nextInBin = curr->nextInBin;
curr = next;
next = next->nextInBin;
}
// If we didn't remove the last item, we're done
if (curr != last)
return last;
// if we removed the last item, the new last item is prev
// fix it up since it might be stale and return it
prev->nextBin = last->nextBin;
return prev;
// remove next from the 'in bin' list since it's what we're looking for
curr->nextInBin = next->nextInBin;
return top;
}
void
@ -147,8 +142,6 @@ EventQueue::remove(Event *event)
// time as the head)
if (*head == *event) {
head = removeItem(event, head);
if (!head)
head = event->nextBin;
return;
}
@ -163,33 +156,29 @@ EventQueue::remove(Event *event)
if (!curr || *curr != *event)
panic("event not found!");
// curr points to the last item of the the correct 'in bin' list, when
// we remove an item, it returns the new last item (which may be
// curr points to the top item of the the correct 'in bin' list, when
// we remove an item, it returns the new top item (which may be
// unchanged)
Event *last = removeItem(event, curr);
if (!last) {
// The current item was removed, so we need to fix the bin list
prev->nextBin = curr->nextBin;
} else if (last != curr) {
// We have a new last item, so we need to update the bin list
prev->nextBin = last;
}
prev->nextBin = removeItem(event, curr);
}
Event *
EventQueue::serviceOne()
{
// grab the first element
Event *event = head->nextInBin;
Event *event = head;
Event *next = head->nextInBin;
event->clearFlags(Event::Scheduled);
if (head == event) {
if (next) {
// update the next bin pointer since it could be stale
next->nextBin = head->nextBin;
// pop the stack
head = next;
} else {
// this was the only element on the 'in bin' list, so get rid of
// the 'in bin' list and point to the next bin list
head = event->nextBin;
} else {
// maintain head->nextInBin as the first element
head->nextInBin = event->nextInBin;
head = head->nextBin;
}
// handle action
@ -247,16 +236,16 @@ EventQueue::serialize(ostream &os)
int numEvents = 0;
Event *nextBin = head;
while (nextBin) {
Event *nextInBin = nextBin->nextInBin;
Event *nextInBin = nextBin;
do {
while (nextInBin) {
if (nextInBin->getFlags(Event::AutoSerialize)) {
eventPtrs.push_back(nextInBin);
paramOut(os, csprintf("event%d", numEvents++),
nextInBin->name());
}
nextInBin = nextInBin->nextInBin;
} while (nextInBin != nextBin);
}
nextBin = nextBin->nextBin;
}
@ -293,21 +282,16 @@ EventQueue::dump() const
cprintf("EventQueue Dump (cycle %d)\n", curTick);
cprintf("------------------------------------------------------------\n");
m5::hash_map<long, bool> map;
if (empty())
cprintf("<No Events>\n");
else {
Event *nextBin = head;
while (nextBin) {
Event *nextInBin = nextBin;
if (map[reinterpret_cast<long>(nextInBin)])
break;
map[reinterpret_cast<long>(nextInBin)] = true;
do {
nextInBin = nextInBin->nextInBin;
while (nextInBin) {
nextInBin->dump();
} while (nextInBin != nextBin);
nextInBin = nextInBin->nextInBin;
}
nextBin = nextBin->nextBin;
}
@ -326,8 +310,8 @@ EventQueue::debugVerify() const
Event *nextBin = head;
while (nextBin) {
Event *nextInBin = nextBin->nextInBin;
do {
Event *nextInBin = nextBin;
while (nextInBin) {
if (nextInBin->when() < time) {
cprintf("time goes backwards!");
nextInBin->dump();
@ -350,7 +334,7 @@ EventQueue::debugVerify() const
priority = nextInBin->priority();
nextInBin = nextInBin->nextInBin;
} while (nextInBin != nextBin);
}
nextBin = nextBin->nextBin;
}

6
src/sim/eventq.hh
View file

@ -77,8 +77,8 @@ class Event : public Serializable, public FastAlloc
// The event queue is now a linked list of linked lists. The
// 'nextBin' pointer is to find the bin, where a bin is defined as
// when+priority. All events in the same bin will be stored in a
// second circularly linked list maintained by the 'nextInBin'
// pointer. The list will be accessed in FIFO order. The end
// second linked list (a stack) maintained by the 'nextInBin'
// pointer. The list will be accessed in LIFO order. The end
// result is that the insert/removal in 'nextBin' is
// linear/constant, and the lookup/removal in 'nextInBin' is
// constant/constant. Hopefully this is a significant improvement
@ -86,7 +86,7 @@ class Event : public Serializable, public FastAlloc
Event *nextBin;
Event *nextInBin;
friend void insertBefore(Event *event, Event *curr);
friend Event *insertBefore(Event *event, Event *curr);
friend Event *removeItem(Event *event, Event *last);
/// queue to which this event belongs (though it may or may not be