sim: Refactor and simplify the drain API

The drain() call currently passes around a DrainManager pointer, which
is now completely pointless since there is only ever one global
DrainManager in the system. It also contains vestiges from the time
when SimObjects had to keep track of their child objects that needed
draining.

This changeset moves all of the DrainState handling to the Drainable
base class and changes the drain() and drainResume() calls to reflect
this. Particularly, the drain() call has been updated to take no
parameters (the DrainManager argument isn't needed) and return a
DrainState instead of an unsigned integer (there is no point returning
anything other than 0 or 1 any more). Drainable objects should return
either DrainState::Draining (equivalent to returning 1 in the old
system) if they need more time to drain or DrainState::Drained
(equivalent to returning 0 in the old system) if they are already in a
consistent state. Returning DrainState::Running is considered an
error.

Drain done signalling is now done through the signalDrainDone() method
in the Drainable class instead of using the DrainManager directly. The
new call checks if the state of the object is DrainState::Draining
before notifying the drain manager. This means that it is safe to call
signalDrainDone() without first checking if the simulator has
requested draining. The intention here is to reduce the code needed to
implement draining in simple objects.

1 files changed, 16 insertions, 19 deletions

diff --git a/src/mem/dram_ctrl.cc b/src/mem/dram_ctrl.cc
index 0b1509e2f..dc2c03332 100644
--- a/src/mem/dram_ctrl.cc
+++ b/src/mem/dram_ctrl.cc
@@ -61,7 +61,6 @@ DRAMCtrl::DRAMCtrl(const DRAMCtrlParams* p) :
     retryRdReq(false), retryWrReq(false),
     busState(READ),
     nextReqEvent(this), respondEvent(this),
-    drainManager(NULL),
     deviceSize(p->device_size),
     deviceBusWidth(p->device_bus_width), burstLength(p->burst_length),
     deviceRowBufferSize(p->device_rowbuffer_size),
@@ -694,11 +693,11 @@ DRAMCtrl::processRespondEvent()
         schedule(respondEvent, respQueue.front()->readyTime);
     } else {
         // if there is nothing left in any queue, signal a drain
-        if (writeQueue.empty() && readQueue.empty() &&
-            drainManager) {
+        if (drainState() == DrainState::Draining &&
+            writeQueue.empty() && readQueue.empty()) {
+
             DPRINTF(Drain, "DRAM controller done draining\n");
-            drainManager->signalDrainDone();
-            drainManager = NULL;
+            signalDrainDone();
         }
     }
 
@@ -1296,15 +1295,17 @@ DRAMCtrl::processNextReqEvent()
             // trigger writes if we have passed the low threshold (or
             // if we are draining)
             if (!writeQueue.empty() &&
-                (drainManager || writeQueue.size() > writeLowThreshold)) {
+                (drainState() == DrainState::Draining ||
+                 writeQueue.size() > writeLowThreshold)) {
 
                 switch_to_writes = true;
             } else {
                 // check if we are drained
-                if (respQueue.empty () && drainManager) {
+                if (drainState() == DrainState::Draining &&
+                    respQueue.empty()) {
+
                     DPRINTF(Drain, "DRAM controller done draining\n");
-                    drainManager->signalDrainDone();
-                    drainManager = NULL;
+                    signalDrainDone();
                 }
 
                 // nothing to do, not even any point in scheduling an
@@ -1416,7 +1417,7 @@ DRAMCtrl::processNextReqEvent()
         // writes, then switch to reads.
         if (writeQueue.empty() ||
             (writeQueue.size() + minWritesPerSwitch < writeLowThreshold &&
-             !drainManager) ||
+             drainState() != DrainState::Draining) ||
             (!readQueue.empty() && writesThisTime >= minWritesPerSwitch)) {
             // turn the bus back around for reads again
             busState = WRITE_TO_READ;
@@ -2166,28 +2167,24 @@ DRAMCtrl::getSlavePort(const string &if_name, PortID idx)
     }
 }
 
-unsigned int
-DRAMCtrl::drain(DrainManager *dm)
+DrainState
+DRAMCtrl::drain()
 {
     // if there is anything in any of our internal queues, keep track
     // of that as well
-    if (!(writeQueue.empty() && readQueue.empty() &&
-          respQueue.empty())) {
+    if (!(writeQueue.empty() && readQueue.empty() && respQueue.empty())) {
         DPRINTF(Drain, "DRAM controller not drained, write: %d, read: %d,"
                 " resp: %d\n", writeQueue.size(), readQueue.size(),
                 respQueue.size());
-        drainManager = dm;
 
         // the only part that is not drained automatically over time
         // is the write queue, thus kick things into action if needed
         if (!writeQueue.empty() && !nextReqEvent.scheduled()) {
             schedule(nextReqEvent, curTick());
         }
-        setDrainState(DrainState::Draining);
-        return 1;
+        return DrainState::Draining;
     } else {
-        setDrainState(DrainState::Drained);
-        return 0;
+        return DrainState::Drained;
     }
 }