gpu-compute,configs: Make sim exits conditional

The unconditional exit event when a kernel completes that was added in
c644eae2dd is causing scripts that do not
ignore unknown exit events to end simulation prematurely. One such
script is the apu_se.py script used in SE mode GPU simulation. Make this
exit conditional to the parameter being set to a valid value to avoid
this problem.

Change-Id: I1d2c082291fdbcf27390913ffdffb963ec8080dd
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/72098
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
(cherry picked from commit 3756af8ed9)
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/72138
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>

configs/example/gpufs/system/system.py

@@ -115,7 +115,8 @@ def makeGpuFSSystem(args):
         numHWQueues=args.num_hw_queues,
         walker=hsapp_pt_walker,
     )
-    dispatcher = GPUDispatcher()
+    dispatcher_exit_events = True if args.exit_at_gpu_kernel > -1 else False
+    dispatcher = GPUDispatcher(kernel_exit_events=dispatcher_exit_events)
     cp_pt_walker = VegaPagetableWalker()
     gpu_cmd_proc = GPUCommandProcessor(
         hsapp=gpu_hsapp, dispatcher=dispatcher, walker=cp_pt_walker

src/gpu-compute/GPU.py

@@ -328,6 +328,10 @@ class GPUDispatcher(SimObject):
     cxx_class = "gem5::GPUDispatcher"
     cxx_header = "gpu-compute/dispatcher.hh"
 
+    kernel_exit_events = Param.Bool(
+        False, "Enable exiting sim loop after a kernel"
+    )
+
 
 class GPUCommandProcessor(DmaVirtDevice):
     type = "GPUCommandProcessor"

src/gpu-compute/dispatcher.cc

@@ -50,7 +50,8 @@ GPUDispatcher::GPUDispatcher(const Params &p)
     : SimObject(p), shader(nullptr), gpuCmdProc(nullptr),
       tickEvent([this]{ exec(); },
           "GPU Dispatcher tick", false, Event::CPU_Tick_Pri),
-      dispatchActive(false), stats(this)
+      dispatchActive(false), kernelExitEvents(p.kernel_exit_events),
+      stats(this)
 {
     schedule(&tickEvent, 0);
 }
@@ -330,6 +331,10 @@ GPUDispatcher::notifyWgCompl(Wavefront *wf)
         DPRINTF(GPUWgLatency, "Kernel Complete ticks:%d kernel:%d\n",
                 curTick(), kern_id);
         DPRINTF(GPUKernelInfo, "Completed kernel %d\n", kern_id);
+
+        if (kernelExitEvents) {
+            exitSimLoop("GPU Kernel Completed");
+        }
     }
 
     if (!tickEvent.scheduled()) {

src/gpu-compute/dispatcher.hh

@@ -92,6 +92,8 @@ class GPUDispatcher : public SimObject
     std::queue<int> doneIds;
     // is there a kernel in execution?
     bool dispatchActive;
+    // Enable exiting sim loop after each kernel completion
+    bool kernelExitEvents;
 
   protected:
     struct GPUDispatcherStats : public statistics::Group