gpu-compute: Change kernel-based exit location (#184)

The previous exit event occurs when the dispatcher sends a completion
signal for a kernel, but gem5 does some kernel-based stats updates after
the signal is sent. Therefore, if these exit events are used as a way to
dump per-kernel stats, some of the stats for the kernel that just ended
will be in the next kernel's stat dump which is misleading.

This patch moves the exit event to where the stats are updated and only
exits if the dispatcher has requested a stat dump to prevent situations
where stats are updated mid-kernel.

Change-Id: I74dc1cad5fc90382a2a80564764b3e7c9fb65521

src/gpu-compute/dispatcher.cc

@@ -334,7 +334,7 @@ GPUDispatcher::notifyWgCompl(Wavefront *wf)
         DPRINTF(GPUKernelInfo, "Completed kernel %d\n", kern_id);
 
         if (kernelExitEvents) {
-            exitSimLoop("GPU Kernel Completed");
+            shader->requestKernelExitEvent();
         }
     }
 

src/gpu-compute/shader.cc

@@ -519,8 +519,14 @@ Shader::notifyCuSleep() {
     panic_if(_activeCus <= 0 || _activeCus > cuList.size(),
              "Invalid activeCu size\n");
     _activeCus--;
-    if (!_activeCus)
+    if (!_activeCus) {
         stats.shaderActiveTicks += curTick() - _lastInactiveTick;
+
+        if (kernelExitRequested) {
+            kernelExitRequested = false;
+            exitSimLoop("GPU Kernel Completed");
+        }
+    }
 }
 
 /**

src/gpu-compute/shader.hh

@@ -97,6 +97,10 @@ class Shader : public ClockedObject
     // Last tick that all CUs attached to this shader were inactive
     Tick _lastInactiveTick;
 
+    // If a kernel-based exit event was requested, wait for all CUs in the
+    // shader to complete before actually exiting so that stats are updated.
+    bool kernelExitRequested = false;
+
   public:
     typedef ShaderParams Params;
     enum hsail_mode_e {SIMT,VECTOR_SCALAR};
@@ -314,6 +318,12 @@ class Shader : public ClockedObject
         stats.vectorInstDstOperand[num_operands]++;
     }
 
+    void
+    requestKernelExitEvent()
+    {
+        kernelExitRequested = true;
+    }
+
   protected:
     struct ShaderStats : public statistics::Group
     {