arch-arm: Add support to exit the simloop on PMU interrupt

Add an option `exitOnPMUInterrupt` to ArmPMU.

The PMU is often used to identify and demark regions of interest in a
workload intended for sampled simulation (e.g. fast-forward, warm-up,
detailed simulation). Often the PMU is enabled and disabled to demark
these regions, but for some workloads PMU interrupts are used to count
committed instructions directly.

This patch adds the option to exit the simulation loop when a PMU
interrupt is triggered so additional simulation control can be
effected (e.g. stats dump/reset, CPU switch, etc).

Change-Id: Ife02fe8e467dec91a2d4fda3f7dc9540a092f1ec
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/69958
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>

src/arch/arm/ArmPMU.py

@@ -218,6 +218,7 @@ class ArmPMU(SimObject):
     exitOnPMUControl = Param.Bool(
         False, "Exit on PMU enable, disable, or reset"
     )
+    exitOnPMUInterrupt = Param.Bool(False, "Exit on PMU interrupt")
 
     # 64-bit PMU event counters are officially supported when
     # Armv8.5-A FEAT_PMUv3p5 is implemented. This parameter is not a

src/arch/arm/pmu.cc

@@ -68,7 +68,8 @@ PMU::PMU(const ArmPMUParams &p)
       swIncrementEvent(nullptr),
       reg_pmcr_conf(0),
       interrupt(nullptr),
-      exitOnPMUControl(p.exitOnPMUControl)
+      exitOnPMUControl(p.exitOnPMUControl),
+      exitOnPMUInterrupt(p.exitOnPMUInterrupt)
 {
     DPRINTF(PMUVerbose, "Initializing the PMU.\n");
 
@@ -677,6 +678,10 @@ PMU::setOverflowStatus(RegVal new_val)
 void
 PMU::raiseInterrupt()
 {
+    if (exitOnPMUInterrupt) {
+        inform("Exiting simulation: PMU interrupt detected");
+        exitSimLoop("performance counter interrupt", 0);
+    }
     if (interrupt) {
         DPRINTF(PMUVerbose, "Delivering PMU interrupt.\n");
         interrupt->raise();

src/arch/arm/pmu.hh

@@ -638,6 +638,10 @@ class PMU : public SimObject, public ArmISA::BaseISADevice
      */
     const bool exitOnPMUControl;
 
+    /**
+     * Exit simloop on PMU interrupt
+     */
+    bool exitOnPMUInterrupt;
 };
 
 } // namespace ArmISA

src/python/gem5/simulate/exit_event.py

@@ -52,6 +52,7 @@ class ExitEvent(Enum):
     PERF_COUNTER_ENABLE = "performance counter enabled"
     PERF_COUNTER_DISABLE = "performance counter disabled"
     PERF_COUNTER_RESET = "performance counter reset"
+    PERF_COUNTER_INTERRUPT = "performance counter interrupt"
 
     @classmethod
     def translate_exit_status(cls, exit_string: str) -> "ExitEvent":
@@ -99,6 +100,8 @@ class ExitEvent(Enum):
             return ExitEvent.PERF_COUNTER_DISABLE
         elif exit_string == "performance counter reset":
             return ExitEvent.PERF_COUNTER_RESET
+        elif exit_string == "performance counter interrupt":
+            return ExitEvent.PERF_COUNTER_INTERRUPT
         elif exit_string.endswith("will terminate the simulation.\n"):
             # This is for the traffic generator exit event
             return ExitEvent.EXIT