kvm: Separate host frequency from simulated CPU frequency

We used to use the KVM CPU's clock to specify the host frequency. This
was not ideal for several reasons. One of them being that the clock
parameter of a CPU determines the frequency of some of the components
connected to the CPU. This changeset adds a separate hostFreq
parameter that should be used to specify the host frequency until we
add code to autodetect it. The hostFactor should still be used to
specify the conversion factor between the host performance and that of
the simulated system.

src/cpu/kvm/BaseKvmCPU.py

@@ -71,4 +71,6 @@ class BaseKvmCPU(BaseCPU):
     kvmVM = Param.KvmVM(Parent.any, 'KVM VM (i.e., shared memory domain)')
     useCoalescedMMIO = Param.Bool(False, "Use coalesced MMIO (EXPERIMENTAL)")
     usePerfOverflow = Param.Bool(False, "Use perf event overflow counters (EXPERIMENTAL)")
+
+    hostFreq = Param.Clock("2GHz", "Host clock frequency")
     hostFactor = Param.Float(1.0, "Cycle scale factor")

src/cpu/kvm/base.cc

@@ -83,6 +83,7 @@ BaseKvmCPU::BaseKvmCPU(BaseKvmCPUParams *params)
       pageSize(sysconf(_SC_PAGE_SIZE)),
       tickEvent(*this),
       perfControlledByTimer(params->usePerfOverflow),
+      hostFreq(params->hostFreq),
       hostFactor(params->hostFactor),
       drainManager(NULL),
       ctrInsts(0)
@@ -103,11 +104,11 @@ BaseKvmCPU::BaseKvmCPU(BaseKvmCPUParams *params)
         runTimer.reset(new PerfKvmTimer(hwCycles,
                                         KVM_TIMER_SIGNAL,
                                         params->hostFactor,
-                                        params->clock));
+                                        params->hostFreq));
     else
         runTimer.reset(new PosixKvmTimer(KVM_TIMER_SIGNAL, CLOCK_MONOTONIC,
                                          params->hostFactor,
-                                         params->clock));
+                                         params->hostFreq));
 }
 
 BaseKvmCPU::~BaseKvmCPU()
@@ -410,8 +411,7 @@ BaseKvmCPU::activateContext(ThreadID thread_num, Cycles delay)
     assert(_status == Idle);
     assert(!tickEvent.scheduled());
 
-    numCycles += ticksToCycles(thread->lastActivate - thread->lastSuspend)
-        * hostFactor;
+    numCycles += ticksToCycles(thread->lastActivate - thread->lastSuspend);
 
     schedule(tickEvent, clockEdge(delay));
     _status = Running;

src/cpu/kvm/base.hh

@@ -670,6 +670,10 @@ class BaseKvmCPU : public BaseCPU
      */
     std::unique_ptr<BaseKvmTimer> runTimer;
 
+    /** Host frequency */
+    Tick hostFreq;
+
+    /** Host factor as specified in the configuration */
     float hostFactor;
 
     /**