cpu: Fix broken thread context handover

The thread context handover code used to break when multiple handovers
were performed during the same quiesce period. Previously, the thread
contexts would assign the TC pointer in the old quiesce event to the
new TC. This obviously broke in cases where multiple switches were
performed within the same quiesce period, in which case the TC pointer
in the quiesce event would point to an old CPU.

The new implementation deschedules pending quiesce events in the old
TC and schedules a new quiesce event in the new TC. The code has been
refactored to remove most of the code duplication.

src/cpu/inorder/thread_context.cc

@@ -93,18 +93,10 @@ InOrderThreadContext::profileSample()
 void
 InOrderThreadContext::takeOverFrom(ThreadContext *old_context)
 {
-    // some things should already be set up
-    assert(getSystemPtr() == old_context->getSystemPtr());
-    assert(getProcessPtr() == old_context->getProcessPtr());
-
-    // copy over functional state
-    setStatus(old_context->status());
-    copyArchRegs(old_context);
+    ::takeOverFrom(*this, *old_context);
 
     thread->funcExeInst = old_context->readFuncExeInst();
 
-    old_context->setStatus(ThreadContext::Halted);
-
     thread->noSquashFromTC = false;
     thread->trapPending = false;
 }

src/cpu/o3/thread_context_impl.hh

@@ -66,34 +66,10 @@ template <class Impl>
 void
 O3ThreadContext<Impl>::takeOverFrom(ThreadContext *old_context)
 {
-    // some things should already be set up
-    assert(getSystemPtr() == old_context->getSystemPtr());
-    assert(getProcessPtr() == old_context->getProcessPtr());
+    ::takeOverFrom(*this, *old_context);
 
-    // copy over functional state
-    setStatus(old_context->status());
-    copyArchRegs(old_context);
-    setContextId(old_context->contextId());
-    setThreadId(old_context->threadId());
-
-    if (FullSystem) {
-        EndQuiesceEvent *other_quiesce = old_context->getQuiesceEvent();
-        if (other_quiesce) {
-            // Point the quiesce event's TC at this TC so that it wakes up
-            // the proper CPU.
-            other_quiesce->tc = this;
-        }
-        if (thread->quiesceEvent) {
-            thread->quiesceEvent->tc = this;
-        }
-
-        // Transfer kernel stats from one CPU to the other.
-        thread->kernelStats = old_context->getKernelStats();
-    } else {
-        thread->funcExeInst = old_context->readFuncExeInst();
-    }
-
-    old_context->setStatus(ThreadContext::Halted);
+    thread->kernelStats = old_context->getKernelStats();
+    thread->funcExeInst = old_context->readFuncExeInst();
 
     thread->noSquashFromTC = false;
     thread->trapPending = false;

src/cpu/simple_thread.cc

@@ -107,49 +107,11 @@ SimpleThread::~SimpleThread()
 void
 SimpleThread::takeOverFrom(ThreadContext *oldContext)
 {
-    // some things should already be set up
-    if (FullSystem)
-        assert(system == oldContext->getSystemPtr());
-    assert(process == oldContext->getProcessPtr());
-
-    copyState(oldContext);
-    if (FullSystem) {
-        EndQuiesceEvent *quiesce = oldContext->getQuiesceEvent();
-        if (quiesce) {
-            // Point the quiesce event's TC at this TC so that it wakes up
-            // the proper CPU.
-            quiesce->tc = tc;
-        }
-        if (quiesceEvent) {
-            quiesceEvent->tc = tc;
-        }
-
-        TheISA::Kernel::Statistics *stats = oldContext->getKernelStats();
-        if (stats) {
-            kernelStats = stats;
-        }
-    }
+    ::takeOverFrom(*tc, *oldContext);
 
+    kernelStats = oldContext->getKernelStats();
+    funcExeInst = oldContext->readFuncExeInst();
     storeCondFailures = 0;
-
-    oldContext->setStatus(ThreadContext::Halted);
-}
-
-void
-SimpleThread::copyTC(ThreadContext *context)
-{
-    copyState(context);
-
-    if (FullSystem) {
-        EndQuiesceEvent *quiesce = context->getQuiesceEvent();
-        if (quiesce) {
-            quiesceEvent = quiesce;
-        }
-        TheISA::Kernel::Statistics *stats = context->getKernelStats();
-        if (stats) {
-            kernelStats = stats;
-        }
-    }
 }
 
 void

src/cpu/simple_thread.hh

@@ -146,8 +146,6 @@ class SimpleThread : public ThreadState
 
     void regStats(const std::string &name);
 
-    void copyTC(ThreadContext *context);
-
     void copyState(ThreadContext *oldContext);
 
     void serialize(std::ostream &os);

src/cpu/thread_context.cc

@@ -43,8 +43,11 @@
 #include "base/misc.hh"
 #include "base/trace.hh"
 #include "config/the_isa.hh"
+#include "cpu/base.hh"
+#include "cpu/quiesce_event.hh"
 #include "cpu/thread_context.hh"
 #include "debug/Context.hh"
+#include "sim/full_system.hh"
 
 void
 ThreadContext::compare(ThreadContext *one, ThreadContext *two)
@@ -136,3 +139,37 @@ unserialize(ThreadContext &tc, Checkpoint *cp, const std::string &section)
 
     // thread_num and cpu_id are deterministic from the config
 }
+
+void
+takeOverFrom(ThreadContext &ntc, ThreadContext &otc)
+{
+    assert(ntc.getProcessPtr() == otc.getProcessPtr());
+
+    ntc.setStatus(otc.status());
+    ntc.copyArchRegs(&otc);
+    ntc.setContextId(otc.contextId());
+    ntc.setThreadId(otc.threadId());
+
+    if (FullSystem) {
+        assert(ntc.getSystemPtr() == otc.getSystemPtr());
+
+        BaseCPU *ncpu(ntc.getCpuPtr());
+        assert(ncpu);
+        EndQuiesceEvent *oqe(otc.getQuiesceEvent());
+        assert(oqe);
+        assert(oqe->tc == &otc);
+
+        BaseCPU *ocpu(otc.getCpuPtr());
+        assert(ocpu);
+        EndQuiesceEvent *nqe(ntc.getQuiesceEvent());
+        assert(nqe);
+        assert(nqe->tc == &ntc);
+
+        if (oqe->scheduled()) {
+            ncpu->schedule(nqe, oqe->when());
+            ocpu->deschedule(oqe);
+        }
+    }
+
+    otc.setStatus(ThreadContext::Halted);
+}

src/cpu/thread_context.hh

@@ -481,4 +481,17 @@ void unserialize(ThreadContext &tc, Checkpoint *cp, const std::string &section);
 
 /** @} */
 
+
+/**
+ * Copy state between thread contexts in preparation for CPU handover.
+ *
+ * @note This method modifies the old thread contexts as well as the
+ * new thread context. The old thread context will have its quiesce
+ * event descheduled if it is scheduled and its status set to halted.
+ *
+ * @param new_tc Destination ThreadContext.
+ * @param old_tc Source ThreadContext.
+ */
+void takeOverFrom(ThreadContext &new_tc, ThreadContext &old_tc);
+
 #endif