From 440029c9d17726da9776f35e66da869e843e2faf Mon Sep 17 00:00:00 2001
From: Andreas Kling <awesomekling@gmail.com>
Date: Wed, 7 Nov 2018 22:24:20 +0100
Subject: [PATCH] Reduce number of passes in the scheduler by 2.

---
 Kernel/Process.cpp   |  8 ++++++--
 Kernel/Scheduler.cpp | 31 +++++++++++++++++--------------
 2 files changed, 23 insertions(+), 16 deletions(-)

diff --git a/Kernel/Process.cpp b/Kernel/Process.cpp
index 912a6b97ab..bb8b9f099e 100644
--- a/Kernel/Process.cpp
+++ b/Kernel/Process.cpp
@@ -857,20 +857,24 @@ void Process::doHouseKeeping()
 void Process::for_each(Function<bool(Process&)> callback)
 {
     ASSERT_INTERRUPTS_DISABLED();
-    for (auto* process = g_processes->head(); process; process = process->next()) {
+    for (auto* process = g_processes->head(); process;) {
+        auto* next_process = process->next();
         if (!callback(*process))
             break;
+        process = next_process;
     }
 }
 
 void Process::for_each_in_pgrp(pid_t pgid, Function<bool(Process&)> callback)
 {
     ASSERT_INTERRUPTS_DISABLED();
-    for (auto* process = g_processes->head(); process; process = process->next()) {
+    for (auto* process = g_processes->head(); process;) {
+        auto* next_process = process->next();
         if (process->pgid() == pgid) {
             if (!callback(*process))
                 break;
         }
+        process = next_process;
     }
 }
 
diff --git a/Kernel/Scheduler.cpp b/Kernel/Scheduler.cpp
index dbe045f8cb..338490f632 100644
--- a/Kernel/Scheduler.cpp
+++ b/Kernel/Scheduler.cpp
@@ -2,6 +2,7 @@
 #include "Process.h"
 #include "system.h"
 
+//#define LOG_EVERY_CONTEXT_SWITCH
 //#define SCHEDULER_DEBUG
 
 static const dword time_slice = 5; // *10 = 50ms
@@ -48,22 +49,20 @@ bool Scheduler::pick_next()
                 process.unblock();
             return true;
         }
-        return true;
-    });
 
-    // Forgive dead orphans.
-    // FIXME: Does this really make sense?
-    Process::for_each_in_state(Process::Dead, [] (auto& process) {
-        if (!Process::from_pid(process.ppid()))
-            process.set_state(Process::Forgiven);
-        return true;
-    });
+        // Forgive dead orphans.
+        if (process.state() == Process::Dead) {
+            if (!Process::from_pid(process.ppid()))
+                process.set_state(Process::Forgiven);
+        }
+
+        // Release the forgiven.
+        Process::for_each_in_state(Process::Forgiven, [] (auto& process) {
+            g_processes->remove(&process);
+            g_dead_processes->append(&process);
+            return true;
+        });
 
-    // Clean up forgiven processes.
-    // FIXME: Do we really need this to be a separate pass over the process list?
-    Process::for_each_in_state(Process::Forgiven, [] (auto& process) {
-        g_processes->remove(&process);
-        g_dead_processes->append(&process);
         return true;
     });
 
@@ -178,6 +177,10 @@ bool Scheduler::context_switch(Process& process)
         // mark it as runnable for the next round.
         if (current->state() == Process::Running)
             current->set_state(Process::Runnable);
+
+#ifdef LOG_EVERY_CONTEXT_SWITCH
+        dbgprintf("Scheduler: %s(%u) -> %s(%u)\n", current->name().characters(), current->pid(), process.name().characters(), process.pid());
+#endif
     }
 
     current = &process;