cpu: Add cpuIdlePins to indicate the threadContext of CPU is idle (#1285)

If the threacContext of CPU enters the suspend mode, raise the threadID
of threadContext cpu_idle_pins with the high signal to target. If the
threadContext of CPU enters the activate mode, lower the threadID of
thread cpu_idle_pins with low signal to target.

src/cpu/BaseCPU.py

@@ -45,6 +45,7 @@ from m5.objects.ClockDomain import *
 from m5.objects.ClockedObject import ClockedObject
 from m5.objects.CPUTracers import ExeTracer
 from m5.objects.InstTracer import InstTracer
+from m5.objects.IntPin import VectorIntSourcePin
 from m5.objects.Platform import Platform
 from m5.objects.ResetPort import ResetResponsePort
 from m5.objects.SubSystem import SubSystem
@@ -155,6 +156,13 @@ class BaseCPU(ClockedObject):
 
     model_reset = ResetResponsePort("Generic reset for the CPU")
 
+    cpu_idle_pins = VectorIntSourcePin(
+        "This signal indicates the thread context of CPU is idle. Should be "
+        "equal to the numThreads or keep empty to ignore idle signals. If the "
+        "user specifies cpu_idle_pins less than numThreads. The ContextId "
+        "greater than the size of cpu_idle_pins will be ignored."
+    )
+
     tracer = Param.InstTracer(default_tracer, "Instruction tracer")
 
     icache_port = RequestPort("Instruction Port")

src/cpu/base.cc

@@ -191,6 +191,12 @@ BaseCPU::BaseCPU(const Params &p, bool is_checker)
     modelResetPort.onChange([this](const bool &new_val) {
         setReset(new_val);
     });
+
+    for (int i = 0; i < params().port_cpu_idle_pins_connection_count; i++) {
+        cpuIdlePins.emplace_back(new IntSourcePin<BaseCPU>(
+            csprintf("%s.cpu_idle_pins[%d]", name(), i), i, this));
+    }
+
     // create a stat group object for each thread on this core
     fetchStats.reserve(numThreads);
     executeStats.reserve(numThreads);
@@ -463,6 +469,8 @@ BaseCPU::getPort(const std::string &if_name, PortID idx)
         return getInstPort();
     else if (if_name == "model_reset")
         return modelResetPort;
+    else if (if_name == "cpu_idle_pins")
+        return *cpuIdlePins[idx];
     else
         return ClockedObject::getPort(if_name, idx);
 }
@@ -537,6 +545,11 @@ BaseCPU::activateContext(ThreadID thread_num)
 
     DPRINTF(Thread, "activate contextId %d\n",
             threadContexts[thread_num]->contextId());
+
+    if (thread_num < cpuIdlePins.size()) {
+        cpuIdlePins[thread_num]->lower();
+    }
+
     // Squash enter power gating event while cpu gets activated
     if (enterPwrGatingEvent.scheduled())
         deschedule(enterPwrGatingEvent);
@@ -551,6 +564,11 @@ BaseCPU::suspendContext(ThreadID thread_num)
 {
     DPRINTF(Thread, "suspend contextId %d\n",
             threadContexts[thread_num]->contextId());
+
+    if (thread_num < cpuIdlePins.size()) {
+        cpuIdlePins[thread_num]->raise();
+    }
+
     // Check if all threads are suspended
     for (auto t : threadContexts) {
         if (t->status() != ThreadContext::Suspended) {

src/cpu/base.hh

@@ -48,6 +48,7 @@
 #include "arch/generic/interrupts.hh"
 #include "base/statistics.hh"
 #include "debug/Mwait.hh"
+#include "dev/intpin.hh"
 #include "mem/htm.hh"
 #include "mem/port_proxy.hh"
 #include "sim/clocked_object.hh"
@@ -259,6 +260,8 @@ class BaseCPU : public ClockedObject
   protected:
     std::vector<ThreadContext *> threadContexts;
 
+    std::vector<std::unique_ptr<IntSourcePin<BaseCPU>>> cpuIdlePins;
+
     trace::InstTracer * tracer;
 
   public: