config: Move CPU handover logic to m5.switchCpus()

CPU switching consists of the following steps:
 1. Drain the system
 2. Switch out old CPUs (cpu.switchOut())
 3. Change the system timing mode to the mode the new CPUs require
 4. Flush caches if switching to hardware virtualization
 5. Inform new CPUs of the handover (cpu.takeOverFrom())
 6. Resume the system

m5.switchCpus() previously only did step 2 & 5. Since information
about the new processors' memory system requirements is now exposed,
do all of the steps above.

This patch adds automatic memory system switching and flush (if
needed) to switchCpus(). Additionally, it adds optional draining to
switchCpus(). This has the following implications:

* changeToTiming and changeToAtomic are no longer needed, so they have
  been removed.

* changeMemoryMode is only used internally, so it is has been renamed
  to be private.

* switchCpus requires a reference to the system containing the CPUs as
  its first parameter.

WARNING: This changeset breaks compatibility with existing
configuration scripts since it changes the signature of
m5.switchCpus().

src/python/m5/simulate.py

@@ -60,6 +60,11 @@ from util import attrdict
 # define a MaxTick parameter
 MaxTick = 2**63 - 1
 
+_memory_modes = {
+    "atomic" : objects.params.atomic,
+    "timing" : objects.params.timing,
+    }
+
 # The final hook to generate .ini files.  Called from the user script
 # once the config is built.
 def instantiate(ckpt_dir=None):
@@ -202,7 +207,7 @@ def checkpoint(dir):
     internal.core.serializeAll(dir)
     resume(root)
 
-def changeMemoryMode(system, mode):
+def _changeMemoryMode(system, mode):
     if not isinstance(system, (objects.Root, objects.System)):
         raise TypeError, "Parameter of type '%s'.  Must be type %s or %s." % \
               (type(system), objects.Root, objects.System)
@@ -212,15 +217,26 @@ def changeMemoryMode(system, mode):
     else:
         print "System already in target mode. Memory mode unchanged."
 
-def changeToAtomic(system, **kwargs):
-    print "Changing memory mode to atomic"
-    changeMemoryMode(system, objects.params.atomic, **kwargs)
+def switchCpus(system, cpuList, do_drain=True):
+    """Switch CPUs in a system.
 
-def changeToTiming(system, **kwargs):
-    print "Changing memory mode to timing"
-    changeMemoryMode(system, objects.params.timing, **kwargs)
+    By default, this method drains and resumes the system. This
+    behavior can be disabled by setting the keyword argument
+    'do_drain' to false, which might be desirable if multiple
+    operations requiring a drained system are going to be performed in
+    sequence.
 
-def switchCpus(cpuList):
+    Note: This method may switch the memory mode of the system if that
+    is required by the CPUs. It may also flush all caches in the
+    system.
+
+    Arguments:
+      system -- Simulated system.
+      cpuList -- (old_cpu, new_cpu) tuples
+
+    Keyword Arguments:
+      do_drain -- Perform a drain/resume of the system when switching.
+    """
     print "switching cpus"
     if not isinstance(cpuList, list):
         raise RuntimeError, "Must pass a list to this function"
@@ -228,7 +244,10 @@ def switchCpus(cpuList):
         if not isinstance(item, tuple) or len(item) != 2:
             raise RuntimeError, "List must have tuples of (oldCPU,newCPU)"
 
-    old_cpu_set = set([old_cpu for old_cpu, new_cpu in cpuList])
+    old_cpus = [old_cpu for old_cpu, new_cpu in cpuList]
+    new_cpus = [new_cpu for old_cpu, new_cpu in cpuList]
+    old_cpu_set = set(old_cpus)
+    memory_mode_name = new_cpus[0].memory_mode()
     for old_cpu, new_cpu in cpuList:
         if not isinstance(old_cpu, objects.BaseCPU):
             raise TypeError, "%s is not of type BaseCPU" % old_cpu
@@ -240,15 +259,41 @@ def switchCpus(cpuList):
         if not new_cpu.switchedOut():
             raise RuntimeError, \
                 "New CPU (%s) is already active." % (new_cpu,)
+        if not new_cpu.support_take_over():
+            raise RuntimeError, \
+                "New CPU (%s) does not support CPU handover." % (old_cpu,)
+        if new_cpu.memory_mode() != memory_mode_name:
+            raise RuntimeError, \
+                "%s and %s require different memory modes." % (new_cpu,
+                                                               new_cpus[0])
         if old_cpu.switchedOut():
             raise RuntimeError, \
                 "Old CPU (%s) is inactive." % (new_cpu,)
+        if not old_cpu.support_take_over():
+            raise RuntimeError, \
+                "Old CPU (%s) does not support CPU handover." % (old_cpu,)
+
+    try:
+        memory_mode = _memory_modes[memory_mode_name]
+    except KeyError:
+        raise RuntimeError, "Invalid memory mode (%s)" % memory_mode_name
+
+    if do_drain:
+        drain(system)
 
     # Now all of the CPUs are ready to be switched out
     for old_cpu, new_cpu in cpuList:
         old_cpu.switchOut()
 
+    # Change the memory mode if required. We check if this is needed
+    # to avoid printing a warning if no switch was performed.
+    if system.getMemoryMode() != memory_mode:
+        _changeMemoryMode(system, memory_mode)
+
     for old_cpu, new_cpu in cpuList:
         new_cpu.takeOverFrom(old_cpu)
 
+    if do_drain:
+        resume(system)
+
 from internal.core import disableAllListeners