ruby: Check MessageBuffer space in garnet NetworkInterface

Garnet's NetworkInterface does not consider the size of MessageBuffers when
ejecting a Message from the network. Add a size check for the MessageBuffer
and only enqueue if space is available. If space is not available, the
message if placed in a queue and the credit is held. A callback from the
MessageBuffer is implemented to wake the NetworkInterface. If there are
messages in the stalled queue, they are processed first, in a FIFO manner
and if succesfully ejected, the credit is finally sent back upstream. The
maximum size of the stall queue is equal to the number of valid VNETs
with MessageBuffers attached.

1 files changed, 19 insertions, 0 deletions

diff --git a/src/mem/ruby/network/MessageBuffer.cc b/src/mem/ruby/network/MessageBuffer.cc
index 573d8833a..67bc7f72d 100644
--- a/src/mem/ruby/network/MessageBuffer.cc
+++ b/src/mem/ruby/network/MessageBuffer.cc
@@ -60,6 +60,8 @@ MessageBuffer::MessageBuffer(const Params *p)
 
     m_buf_msgs = 0;
     m_stall_time = 0;
+
+    m_dequeue_callback = nullptr;
 }
 
 unsigned int
@@ -241,10 +243,27 @@ MessageBuffer::dequeue(Tick current_time, bool decrement_messages)
         m_buf_msgs--;
     }
 
+    // if a dequeue callback was requested, call it now
+    if (m_dequeue_callback) {
+        m_dequeue_callback();
+    }
+
     return delay;
 }
 
 void
+MessageBuffer::registerDequeueCallback(std::function<void()> callback)
+{
+    m_dequeue_callback = callback;
+}
+
+void
+MessageBuffer::unregisterDequeueCallback()
+{
+    m_dequeue_callback = nullptr;
+}
+
+void
 MessageBuffer::clear()
 {
     m_prio_heap.clear();