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mem-ruby: Do not change blocked msg enqueue info

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Updating the message counter and enqueue times when adding blocked
messages back to the queue does not make a lot of sense since these
messages are not new arrivals.
More importantly, this may lead to starvation. See the scenario below:

1) Request A for a blocked line X arrives
2) A is handled; X is blocked so A is stalled
3) Request B for X arrives; Reponse for X arrives
4) Response is handled; X unblocked; A added back to the request queue
5) B is handled ahead of A (since A's arrival was updated);
   X may become blocked again

If new requests keep comming for X, A may will be stalled forever.

Change-Id: Icad79f3f716a870e91cb3455437b8b3c35f130ac
Signed-off-by: Tiago Muck <tiago.muck@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18412
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Matthew Poremba <matthew.poremba@amd.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
This commit is contained in:
Tiago Muck
2019-02-25 16:20:32 -06:00
committed by Tiago Mück
parent 575ac7a14a
commit 42e55cdafd
1 changed files with 5 additions and 3 deletions
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8
src/mem/ruby/network/MessageBuffer.cc
View File

@@ -297,16 +297,18 @@ void
MessageBuffer::reanalyzeList(list<MsgPtr> &lt, Tick schdTick)
{
while (!lt.empty()) {
m_msg_counter++;
MsgPtr m = lt.front();
m->setLastEnqueueTime(schdTick);
m->setMsgCounter(m_msg_counter);
assert(m->getLastEnqueueTime() <= schdTick);
m_prio_heap.push_back(m);
push_heap(m_prio_heap.begin(), m_prio_heap.end(),
greater<MsgPtr>());
m_consumer->scheduleEventAbsolute(schdTick);
DPRINTF(RubyQueue, "Requeue arrival_time: %lld, Message: %s\n",
schdTick, *(m.get()));
lt.pop_front();
}
}