O3 CPU: Strengthen condition for handling interrupts

The condition for handling interrupts is to check whether or not the cpu's
instruction list is empty. As observed, this can lead to cases in which even
though the instruction list is empty, interrupts are handled when they should
not be. The condition is being strengthened so that interrupts get handled only
when the last committed microop did not had IsDelayedCommit set.

src/cpu/o3/commit.hh

@@ -441,6 +441,9 @@ class DefaultCommit
     /** Rename map interface. */
     RenameMap *renameMap[Impl::MaxThreads];
 
+    /** True if last committed microop can be followed by an interrupt */
+    bool canHandleInterrupts;
+
     /** Updates commit stats based on this instruction. */
     void updateComInstStats(DynInstPtr &inst);
 

src/cpu/o3/commit_impl.hh

@@ -105,7 +105,8 @@ DefaultCommit<Impl>::DefaultCommit(O3CPU *_cpu, DerivO3CPUParams *params)
       numThreads(params->numThreads),
       drainPending(false),
       switchedOut(false),
-      trapLatency(params->trapLatency)
+      trapLatency(params->trapLatency),
+      canHandleInterrupts(true)
 {
     _status = Active;
     _nextStatus = Inactive;
@@ -714,7 +715,7 @@ DefaultCommit<Impl>::handleInterrupt()
 
     // Wait until all in flight instructions are finished before enterring
     // the interrupt.
-    if (cpu->instList.empty()) {
+    if (canHandleInterrupts && cpu->instList.empty()) {
         // Squash or record that I need to squash this cycle if
         // an interrupt needed to be handled.
         DPRINTF(Commit, "Interrupt detected.\n");
@@ -743,7 +744,10 @@ DefaultCommit<Impl>::handleInterrupt()
 
         interrupt = NoFault;
     } else {
-        DPRINTF(Commit, "Interrupt pending, waiting for ROB to empty.\n");
+        DPRINTF(Commit, "Interrupt pending: instruction is %sin "
+                "flight, ROB is %sempty\n",
+                canHandleInterrupts ? "not " : "",
+                cpu->instList.empty() ? "" : "not " );
     }
 }
 
@@ -775,11 +779,6 @@ void
 DefaultCommit<Impl>::commit()
 {
     if (FullSystem) {
-        // Check for any interrupt that we've already squashed for and
-        // start processing it.
-        if (interrupt != NoFault)
-            handleInterrupt();
-
         // Check if we have a interrupt and get read to handle it
         if (cpu->checkInterrupts(cpu->tcBase(0)))
             propagateInterrupt();
@@ -936,6 +935,11 @@ DefaultCommit<Impl>::commitInsts()
     // Commit as many instructions as possible until the commit bandwidth
     // limit is reached, or it becomes impossible to commit any more.
     while (num_committed < commitWidth) {
+        // Check for any interrupt that we've already squashed for
+        // and start processing it.
+        if (interrupt != NoFault)
+            handleInterrupt();
+
         int commit_thread = getCommittingThread();
 
         if (commit_thread == -1 || !rob->isHeadReady(commit_thread))
@@ -992,6 +996,12 @@ DefaultCommit<Impl>::commitInsts()
                     cpu->instDone(tid);
                 }
 
+                if (tid == 0) {
+                    canHandleInterrupts =  (!head_inst->isDelayedCommit()) &&
+                                           ((THE_ISA != ALPHA_ISA) ||
+                                             (!(pc[0].instAddr() & 0x3)));
+                }
+
                 // Updates misc. registers.
                 head_inst->updateMiscRegs();
 

src/cpu/o3/fetch_impl.hh

@@ -1144,6 +1144,7 @@ DefaultFetch<Impl>::fetch(bool &status_change)
             // an delayed commit micro-op currently (delayed commit instructions
             // are not interruptable by interrupts, only faults)
             ++fetchMiscStallCycles;
+            DPRINTF(Fetch, "[tid:%i]: Fetch is stalled!\n", tid);
             return;
         }
     } else {