From 321bd0716392c0e11c4cfb9aac9a4d774d8d36f3 Mon Sep 17 00:00:00 2001
From: Yu-Cheng Chang <rogerycchang@google.com>
Date: Fri, 17 May 2024 01:02:53 +0800
Subject: [PATCH] cpu: Don't change to suspend if the thread status is halted
 (#1039)

In our gem5 model, there are four types represent thread context:
Active, Suspend, Halting and Halted


https://github.com/gem5/gem5/blob/5641c5e4642f7d44651f783bdb018d3cf8ba01b5/src/cpu/thread_context.hh#L99-L117

When initializing the gem5 instance, all of the thread contexts are set
Halted. The status of thread context will not be active until the
Workload initializes start up, except the StubWorkload. So if the user
uses the StubWorkload, and the CPU is connected with the model_reset
port. The thread context of the CPU will be activated possibly.

The following is the steps of activating thread context of the CPU
without Workload[1] initialization or lower model_reset port[2].

1. Raise the model_reset port (Change the state from Halted to Suspend)
https://github.com/gem5/gem5/blob/5641c5e4642f7d44651f783bdb018d3cf8ba01b5/src/cpu/base.cc#L671-L673

2. Post the interrupt to CPU (Change the state from Suspend to Active)
https://github.com/gem5/gem5/blob/5641c5e4642f7d44651f783bdb018d3cf8ba01b5/src/cpu/base.cc#L231-L239

Implementation of wakeup

SimpleCPU:

https://github.com/gem5/gem5/blob/5641c5e4642f7d44651f783bdb018d3cf8ba01b5/src/cpu/simple/base.cc#L251-L259

MinorCPU:

https://github.com/gem5/gem5/blob/5641c5e4642f7d44651f783bdb018d3cf8ba01b5/src/cpu/minor/cpu.cc#L143-L151

O3CPU:

https://github.com/gem5/gem5/blob/5641c5e4642f7d44651f783bdb018d3cf8ba01b5/src/cpu/o3/cpu.cc#L1337-L1346

This CL fixed the issue when raising the model reset port to CPU(let CPU
sleep) if the CPU is not activated by workload. If the CPU status is
halted, it's should not change to Suspend to avoid wake up

Reference

The model_reset is introduced in the CL:
https://gem5-review.googlesource.com/c/public/gem5/+/67574/4

[1] Activate by workload (ARM example):

https://github.com/gem5/gem5/blob/5641c5e4642f7d44651f783bdb018d3cf8ba01b5/src/arch/arm/fs_workload.cc#L101-L114

[2] Lower the model_reset:

https://github.com/gem5/gem5/blob/5641c5e4642f7d44651f783bdb018d3cf8ba01b5/src/cpu/base.cc#L191-L192
https://github.com/gem5/gem5/blob/5641c5e4642f7d44651f783bdb018d3cf8ba01b5/src/cpu/base.cc#L674-L685

Change-Id: I5bfc0b7491d14369fff77b98b71c0ac763fb7c42
---
 src/cpu/o3/thread_context.cc | 4 +++-
 src/cpu/simple_thread.cc     | 3 ++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/cpu/o3/thread_context.cc b/src/cpu/o3/thread_context.cc
index 06210de07e..2eac107c99 100644
--- a/src/cpu/o3/thread_context.cc
+++ b/src/cpu/o3/thread_context.cc
@@ -86,7 +86,9 @@ ThreadContext::suspend()
     DPRINTF(O3CPU, "Calling suspend on Thread Context %d\n",
             threadId());
 
-    if (thread->status() == gem5::ThreadContext::Suspended)
+    if (thread->status() == gem5::ThreadContext::Suspended ||
+        thread->status() == gem5::ThreadContext::Halting ||
+        thread->status() == gem5::ThreadContext::Halted)
         return;
 
     if (cpu->isDraining()) {
diff --git a/src/cpu/simple_thread.cc b/src/cpu/simple_thread.cc
index c28359a4ed..9e90ce45b8 100644
--- a/src/cpu/simple_thread.cc
+++ b/src/cpu/simple_thread.cc
@@ -143,7 +143,8 @@ SimpleThread::activate()
 void
 SimpleThread::suspend()
 {
-    if (status() == ThreadContext::Suspended)
+    if (status() == ThreadContext::Suspended ||
+        status() == ThreadContext::Halted)
         return;
 
     lastActivate = curTick();