Clock: Rework clocks to avoid tick-to-cycle transformations

This patch introduces the notion of a clock update function that aims
to avoid costly divisions when turning the current tick into a
cycle. Each clocked object advances a private (hidden) cycle member
and a tick member and uses these to implement functions for getting
the tick of the next cycle, or the tick of a cycle some time in the
future.

In the different modules using the clocks, changes are made to avoid
counting in ticks only to later translate to cycles. There are a few
oddities in how the O3 and inorder CPU count idle cycles, as seen by a
few locations where a cycle is subtracted in the calculation. This is
done such that the regression does not change any stats, but should be
revisited in a future patch.

Another, much needed, change that is not done as part of this patch is
to introduce a new typedef uint64_t Cycle to be able to at least hint
at the unit of the variables counting Ticks vs Cycles. This will be
done as a follow-up patch.

As an additional follow up, the thread context still uses ticks for
the book keeping of last activate and last suspend and this should
probably also be changed into cycles as well.

4 files changed, 18 insertions, 21 deletions

diff --git a/src/cpu/inorder/cpu.cc b/src/cpu/inorder/cpu.cc
index 4aff0c579..ec06f19f0 100644
--- a/src/cpu/inorder/cpu.cc
+++ b/src/cpu/inorder/cpu.cc
@@ -212,7 +212,7 @@ void
 InOrderCPU::CPUEvent::scheduleEvent(int delay)
 {
     assert(!scheduled() || squashed());
-    cpu->reschedule(this, cpu->nextCycle(curTick() + cpu->ticks(delay)), true);
+    cpu->reschedule(this, cpu->clockEdge(delay), true);
 }
 
 void
@@ -401,7 +401,7 @@ InOrderCPU::InOrderCPU(Params *params)
     frontEndSked = createFrontEndSked();
     faultSked = createFaultSked();
 
-    lastRunningCycle = curTick();
+    lastRunningCycle = curCycle();
 
     lockAddr = 0;
     lockFlag = false;
@@ -761,17 +761,17 @@ InOrderCPU::tick()
     if (!tickEvent.scheduled()) {
         if (_status == SwitchedOut) {
             // increment stat
-            lastRunningCycle = curTick();
+            lastRunningCycle = curCycle();
         } else if (!activityRec.active()) {
             DPRINTF(InOrderCPU, "sleeping CPU.\n");
-            lastRunningCycle = curTick();
+            lastRunningCycle = curCycle();
             timesIdled++;
         } else {
             //Tick next_tick = curTick() + cycles(1);
             //tickEvent.schedule(next_tick);
-            schedule(&tickEvent, nextCycle(curTick() + 1));
+            schedule(&tickEvent, clockEdge(1));
             DPRINTF(InOrderCPU, "Scheduled CPU for next tick @ %i.\n", 
-                    nextCycle(curTick() + 1));
+                    clockEdge(1));
         }
     }
 
@@ -959,15 +959,10 @@ InOrderCPU::scheduleCpuEvent(CPUEventType c_event, Fault fault,
     CPUEvent *cpu_event = new CPUEvent(this, c_event, fault, tid, inst,
                                        event_pri);
 
-    Tick sked_tick = nextCycle(curTick() + ticks(delay));
-    if (delay >= 0) {
-        DPRINTF(InOrderCPU, "Scheduling CPU Event (%s) for cycle %i, [tid:%i].\n",
-                eventNames[c_event], curTick() + delay, tid);
-        schedule(cpu_event, sked_tick);
-    } else {
-        cpu_event->process();
-        cpuEventRemoveList.push(cpu_event);
-    }
+    Tick sked_tick = clockEdge(delay);
+    DPRINTF(InOrderCPU, "Scheduling CPU Event (%s) for cycle %i, [tid:%i].\n",
+            eventNames[c_event], curTick() + delay, tid);
+    schedule(cpu_event, sked_tick);
 
     // Broadcast event to the Resource Pool
     // Need to reset tid just in case this is a dummy instruction
@@ -1696,7 +1691,9 @@ InOrderCPU::wakeCPU()
 
     DPRINTF(Activity, "Waking up CPU\n");
 
-    Tick extra_cycles = tickToCycles((curTick() - 1) - lastRunningCycle);
+    Tick extra_cycles = curCycle() - lastRunningCycle;
+    if (extra_cycles != 0)
+        --extra_cycles;
 
     idleCycles += extra_cycles;    
     for (int stage_num = 0; stage_num < NumStages; stage_num++) {
@@ -1705,7 +1702,7 @@ InOrderCPU::wakeCPU()
 
     numCycles += extra_cycles;
 
-    schedule(&tickEvent, nextCycle(curTick()));
+    schedule(&tickEvent, nextCycle());
 }
 
 // Lots of copied full system code...place into BaseCPU class?
diff --git a/src/cpu/inorder/cpu.hh b/src/cpu/inorder/cpu.hh
index 3103201dd..9a0a62c87 100644
--- a/src/cpu/inorder/cpu.hh
+++ b/src/cpu/inorder/cpu.hh
@@ -204,7 +204,7 @@ class InOrderCPU : public BaseCPU
     void scheduleTickEvent(int delay)
     {
         assert(!tickEvent.scheduled() || tickEvent.squashed());
-        reschedule(&tickEvent, nextCycle(curTick() + ticks(delay)), true);
+        reschedule(&tickEvent, clockEdge(delay), true);
     }
 
     /** Unschedule tick event, regardless of its current state. */
diff --git a/src/cpu/inorder/resource.cc b/src/cpu/inorder/resource.cc
index 2ddce13c3..098a4e1b4 100644
--- a/src/cpu/inorder/resource.cc
+++ b/src/cpu/inorder/resource.cc
@@ -372,7 +372,7 @@ Resource::ticks(int num_cycles)
 void
 Resource::scheduleExecution(int slot_num)
 {
-    if (latency >= 1) {
+    if (latency > 0) {
         scheduleEvent(slot_num, latency);
     } else {
         execute(slot_num);
diff --git a/src/cpu/inorder/resource_pool.cc b/src/cpu/inorder/resource_pool.cc
index 4c01165b8..31511314e 100644
--- a/src/cpu/inorder/resource_pool.cc
+++ b/src/cpu/inorder/resource_pool.cc
@@ -238,7 +238,7 @@ ResourcePool::scheduleEvent(InOrderCPU::CPUEventType e_type, DynInstPtr inst,
 {
     assert(delay >= 0);
 
-    Tick when = cpu->nextCycle(curTick() + cpu->ticks(delay));
+    Tick when = cpu->clockEdge(delay);
 
     switch ((int)e_type)
     {
@@ -460,7 +460,7 @@ ResourcePool::ResPoolEvent::scheduleEvent(int delay)
 {
     InOrderCPU *cpu = resPool->cpu;
     assert(!scheduled() || squashed());
-    cpu->reschedule(this, cpu->nextCycle(curTick() + cpu->ticks(delay)), true);
+    cpu->reschedule(this, cpu->clockEdge(delay), true);
 }
 
 /** Unschedule resource event, regardless of its current state. */