Initial priority-based scheduler

- Scheduler now has multiple linked_lists of processes at different
  priorities
- Process structure improvements
- scheduler::tick() and scheduler::schedule() separation

assets/initrd.toml

@@ -13,6 +13,11 @@ dest = "screenfont.psf"
 source = "assets/fonts/tamsyn8x16r.psf"
 
 [[files]]
-dest = "nulldrv"
+dest = "nulldrv1"
+source = "build/kernel/src/drivers/nulldrv/nulldrv"
+executable = true
+
+[[files]]
+dest = "nulldrv2"
 source = "build/kernel/src/drivers/nulldrv/nulldrv"
 executable = true

src/drivers/nulldrv/main.s

@@ -3,7 +3,8 @@ _start:
 	xor rbp, rbp	; Sentinel rbp
 
 .loop:
-	mov rax, 0		; DEBUG syscall
+	;mov rax, 1		; DEBUG syscall
+	mov rax, 0		; NOOP syscall
 	syscall
 
 	jmp .loop

src/kernel/interrupts.cpp

@@ -306,6 +306,9 @@ syscall_handler(addr_t return_rsp, cpu_state regs)
 	syscall call = static_cast<syscall>(regs.rax);
 
 	switch (call) {
+	case syscall::noop:
+		break;
+
 	case syscall::debug:
 		cons->set_color(11);
 		cons->printf("\nReceived DEBUG syscall\n");
@@ -314,6 +317,9 @@ syscall_handler(addr_t return_rsp, cpu_state regs)
 		break;
 
 	case syscall::message:
+		cons->set_color(11);
+		cons->printf("\nReceived MESSAGE syscall\n");
+		cons->set_color();
 		break;
 
 	default:

src/kernel/loader.s

@@ -8,8 +8,14 @@ ramdisk_process_loader:
 	; create_process already pushed a cpu_state onto the stack for us, this
 	; acts both as the cpu_state parameter to load_process, and the saved
 	; state for the following iretq
+	;
+	; Additional parameters:
+	;  rax - the address of the program image
+	;  rbx - the size of the program image
+	;  rcx - the address of this process' process structure
 	mov rdi, rax
 	mov rsi, rbx
+	mov rdx, rcx
 	call load_process
 
 	pop_all_and_segments

src/kernel/scheduler.cpp

@@ -20,20 +20,33 @@ const uint64_t rflags_int = 0x202;
 
 extern "C" {
 	void ramdisk_process_loader();
-	void load_process(const void *image_start, size_t butes, cpu_state state);
+	void load_process(const void *image_start, size_t bytes, process *proc, cpu_state state);
 };
 
 scheduler::scheduler(lapic *apic) :
 	m_apic(apic),
-	m_current(0),
+	m_next_pid(1)
-	m_next_pid(0)
 {
-	m_processes.ensure_capacity(50);
+	auto *idle = m_process_allocator.pop();
-	m_processes.append({m_next_pid++, 0, page_manager::get_pml4()}); // The kernel idle task, also the thread we're in now
+
+	uint8_t last_pri = num_priorities - 1;
+
+	// The kernel idle task, also the thread we're in now
+	idle->pid = 0;
+	idle->ppid = 0;
+	idle->priority = last_pri;
+	idle->rsp = 0; // This will get set when we switch away
+	idle->pml4 = page_manager::get_pml4();
+	idle->flags =
+		process_flags::ready |
+		process_flags::const_pri;
+
+	m_runlists[last_pri].push_back(idle);
+	m_current = idle;
 }
 
 void
-load_process(const void *image_start, size_t bytes, cpu_state state)
+load_process(const void *image_start, size_t bytes, process *proc, cpu_state state)
 {
 	// We're now in the process space for this process, allocate memory for the
 	// process code and load it
@@ -85,6 +98,7 @@ load_process(const void *image_start, size_t bytes, cpu_state state)
 	}
 
 	state.rip = image.entrypoint();
+	proc->flags &= ~process_flags::loading;
 
 	log::debug(logs::task, "Loaded! New process state:");
 	log::debug(logs::task, "        CS: %d [%d]", state.cs >> 3, state.cs & 0x07);
@@ -137,14 +151,28 @@ scheduler::create_process(const char *name, const void *data, size_t size)
 	loader_state->rbx = size;
 
 	uint16_t pid = m_next_pid++;
+	auto *proc = m_process_allocator.pop();
+
+	proc->pid = pid;
+	proc->ppid = 0; // TODO
+	proc->priority = default_priority;
+	proc->rsp = reinterpret_cast<addr_t>(loader_state);
+	proc->pml4 = pml4;
+	proc->flags =
+		process_flags::ready |
+		process_flags::loading;
+
+	m_runlists[default_priority].push_back(proc);
+
+	loader_state->rcx = reinterpret_cast<uint64_t>(proc);
+
 	log::debug(logs::task, "Creating process %s:", name);
 	log::debug(logs::task, "      PID %d", pid);
+	log::debug(logs::task, "      Pri %d", pid);
 	log::debug(logs::task, "     RSP0 %016lx", state);
 	log::debug(logs::task, "     RSP3 %016lx", state->user_rsp);
 	log::debug(logs::task, "     PML4 %016lx", pml4);
 	log::debug(logs::task, "  Loading %016lx [%d]", loader_state->rax, loader_state->rbx);
-
-	m_processes.append({pid, reinterpret_cast<addr_t>(loader_state), pml4});
 }
 
 void
@@ -155,21 +183,41 @@ scheduler::start()
 }
 
 addr_t
-scheduler::tick(addr_t rsp0)
+scheduler::schedule(addr_t rsp0)
 {
-	log::debug(logs::task, "Scheduler tick.");
+	m_current->rsp = rsp0;
+	m_runlists[m_current->priority].remove(m_current);
+	m_runlists[m_current->priority].push_back(m_current);
 
-	m_processes[m_current].rsp = rsp0;
+	uint8_t pri = 0;
-	m_current = (m_current + 1) % m_processes.count();
+	while (m_runlists[pri].empty()) {
-	rsp0 = m_processes[m_current].rsp;
+		++pri;
+		kassert(pri < num_priorities, "All runlists are empty");
+	}
+
+	m_current = m_runlists[pri].pop_front();
+	rsp0 = m_current->rsp;
 
 	// Set rsp0 to after the end of the about-to-be-popped cpu state
 	tss_set_stack(0, rsp0 + sizeof(cpu_state));
 
 	// Swap page tables
-	page_table *pml4 = m_processes[m_current].pml4;
+	page_table *pml4 = m_current->pml4;
 	page_manager::set_pml4(pml4);
 
+	bool loading = bitfield_has(m_current->flags, process_flags::loading);
+	log::debug(logs::task, "Scheduler switched to process %d, priority %d%s.",
+			m_current->pid, m_current->priority, loading ? " (loading)" : "");
+
+	return rsp0;
+}
+
+addr_t
+scheduler::tick(addr_t rsp0)
+{
+	// TODO: action based on the task using the whole quantum
+
+	rsp0 = schedule(rsp0);
 	m_apic->reset_timer(quantum);
 	return rsp0;
 }

src/kernel/scheduler.h

@@ -1,25 +1,57 @@
 #pragma once
 /// \file scheduler.h
 /// The task scheduler and related definitions
+#include "kutil/enum_bitfields.h"
+#include "kutil/linked_list.h"
 #include "kutil/memory.h"
+#include "kutil/slab_allocator.h"
 #include "kutil/vector.h"
 
 class lapic;
 struct page_table;
+struct cpu_state;
 
+extern "C" addr_t isr_handler(addr_t, cpu_state);
+
+enum class process_flags : uint32_t
+{
+	running   = 0x00000001,
+	ready     = 0x00000002,
+	loading   = 0x00000004,
+
+	const_pri = 0x80000000,
+
+	none      = 0x00000000
+};
+IS_BITFIELD(process_flags);
 
 struct process
 {
-	uint16_t pid;
+	uint32_t pid;
+	uint32_t ppid;
+
+	uint8_t priority;
+
+	uint8_t reserved0;
+	uint16_t reserved;
+
+	process_flags flags;
+
 	addr_t rsp;
 	page_table *pml4;
 };
 
+using process_list = kutil::linked_list<process>;
+using process_node = process_list::item_type;
+using process_slab = kutil::slab_allocator<process>;
 
 /// The task scheduler
 class scheduler
 {
 public:
+	static const uint8_t num_priorities = 8;
+	static const uint8_t default_priority = num_priorities / 2;
+
 	/// Constructor.
 	/// \arg apic  Pointer to the local APIC object
 	scheduler(lapic *apic);
@@ -34,20 +66,34 @@ public:
 	/// timer interrupts or other preemption methods.
 	void start();
 
-	/// Handle a timer tick
+	/// Run the scheduler, possibly switching to a new task
 	/// \arg rsp0  The stack pointer of the current interrupt handler
-	/// \returns   The stack pointer to handler to switch to
+	/// \returns   The stack pointer to switch to
-	addr_t tick(addr_t rsp0);
+	addr_t schedule(addr_t rsp0);
+
+	/// Get the current process.
+	/// \returns  A pointer to the current process' process struct
+	inline process * current() { return m_current; }
 
 	/// Get a reference to the system scheduler
 	/// \returns  A reference to the global system scheduler
 	static scheduler & get() { return s_instance; }
 
 private:
+	friend addr_t isr_handler(addr_t, cpu_state);
+
+	/// Handle a timer tick
+	/// \arg rsp0  The stack pointer of the current interrupt handler
+	/// \returns   The stack pointer to switch to
+	addr_t tick(addr_t rsp0);
+
 	lapic *m_apic;
-	kutil::vector<process> m_processes;
+
-	uint16_t m_current;
+	uint32_t m_next_pid;
-	uint16_t m_next_pid;
+
+	process_node *m_current;
+	process_slab m_process_allocator;
+	process_list m_runlists[num_priorities];
 
 	static scheduler s_instance;
 };

src/kernel/syscall.h

@@ -2,6 +2,7 @@
 
 enum class syscall : uint64_t
 {
+	noop,
 	debug,
 	message,