RubyPort and Sequencer: Fix draining

Fix the drain functionality of the RubyPort to only call drain on child ports
during a system-wide drain process, instead of calling each time that a
ruby_hit_callback is executed.

This fixes the issue of the RubyPort ports being reawakened during the drain
simulation, possibly with work they didn't previously have to complete. If
they have new work, they may call process on the drain event that they had
not registered work for, causing an assertion failure when completing the
drain event.

Also, in RubyPort, set the drainEvent to NULL when there are no events
to be drained. If not set to NULL, the drain loop can result in stale
drainEvents used.

3 files changed, 22 insertions, 20 deletions

diff --git a/src/mem/ruby/system/RubyPort.cc b/src/mem/ruby/system/RubyPort.cc
index d2d82010d..f269f17fe 100644
--- a/src/mem/ruby/system/RubyPort.cc
+++ b/src/mem/ruby/system/RubyPort.cc
@@ -527,7 +527,7 @@ RubyPort::testDrainComplete()
 {
     //If we weren't able to drain before, we might be able to now.
     if (drainEvent != NULL) {
-        unsigned int drainCount = getDrainCount(drainEvent);
+        unsigned int drainCount = outstandingCount();
         DPRINTF(Drain, "Drain count: %u\n", drainCount);
         if (drainCount == 0) {
             DPRINTF(Drain, "RubyPort done draining, processing drain event\n");
@@ -539,21 +539,9 @@ RubyPort::testDrainComplete()
 }
 
 unsigned int
-RubyPort::getDrainCount(Event *de)
+RubyPort::getChildDrainCount(Event *de)
 {
     int count = 0;
-    //
-    // If the sequencer is not empty, then requests need to drain.
-    // The outstandingCount is the number of requests outstanding and thus the
-    // number of times M5's timing port will process the drain event.
-    //
-    count += outstandingCount();
-
-    DPRINTF(Config, "outstanding count %d\n", outstandingCount());
-
-    // To simplify the draining process, the sequencer's deadlock detection
-    // event should have been descheduled.
-    assert(isDeadlockEventScheduled() == false);
 
     if (pio_port.isConnected()) {
         count += pio_port.drain(de);
@@ -583,19 +571,31 @@ RubyPort::drain(Event *de)
         descheduleDeadlockEvent();
     }
 
-    int count = getDrainCount(de);
+    //
+    // If the RubyPort is not empty, then it needs to clear all outstanding
+    // requests before it should call drainEvent->process()
+    //
+    DPRINTF(Config, "outstanding count %d\n", outstandingCount());
+    bool need_drain = outstandingCount() > 0;
+
+    //
+    // Also, get the number of child ports that will also need to clear
+    // their buffered requests before they call drainEvent->process()
+    //
+    unsigned int child_drain_count = getChildDrainCount(de);
 
     // Set status
-    if (count != 0) {
+    if (need_drain) {
         drainEvent = de;
 
         DPRINTF(Drain, "RubyPort not drained\n");
         changeState(SimObject::Draining);
-        return count;
+        return child_drain_count + 1;
     }
 
+    drainEvent = NULL;
     changeState(SimObject::Drained);
-    return 0;
+    return child_drain_count;
 }
 
 void
diff --git a/src/mem/ruby/system/RubyPort.hh b/src/mem/ruby/system/RubyPort.hh
index e57522b5b..bb8ec7852 100644
--- a/src/mem/ruby/system/RubyPort.hh
+++ b/src/mem/ruby/system/RubyPort.hh
@@ -166,7 +166,7 @@ class RubyPort : public MemObject
         }
     }
 
-    unsigned int getDrainCount(Event *de);
+    unsigned int getChildDrainCount(Event *de);
 
     uint16_t m_port_id;
     uint64_t m_request_cnt;
diff --git a/src/mem/ruby/system/Sequencer.cc b/src/mem/ruby/system/Sequencer.cc
index 854d360ac..9b6ef35cd 100644
--- a/src/mem/ruby/system/Sequencer.cc
+++ b/src/mem/ruby/system/Sequencer.cc
@@ -85,6 +85,8 @@ Sequencer::~Sequencer()
 void
 Sequencer::wakeup()
 {
+    assert(getState() != SimObject::Draining);
+
     // Check for deadlock of any of the requests
     Time current_time = g_system_ptr->getTime();
 
@@ -207,7 +209,7 @@ Sequencer::insertRequest(PacketPtr pkt, RubyRequestType request_type)
         (m_writeRequestTable.size() + m_readRequestTable.size()));
 
     // See if we should schedule a deadlock check
-    if (deadlockCheckEvent.scheduled() == false) {
+    if (!deadlockCheckEvent.scheduled() && getState() != SimObject::Draining) {
         schedule(deadlockCheckEvent,
             g_system_ptr->clockPeriod() * m_deadlock_threshold + curTick());
     }