avoid busy waiting if the cpu feature mwait is missing

stlankes · stlankes · commit fea0f310187c · 2017-06-07T21:54:28.000+02:00
diff --git a/arch/x86/kernel/apic.c b/arch/x86/kernel/apic.c
@@ -1033,6 +1033,24 @@ int apic_send_ipi(uint64_t dest, uint8_t irq)
 	return 0;
 }
 
+void wakeup_core(uint32_t core_id)
+{
+	// if mwait is available, an IPI isn't required to wakeup the core
+	if (has_mwait())
+		return;
+
+	// no self IPI required
+	if (core_id == CORE_ID)
+		return;
+
+	// no IPI required if core is offline
+	if (!online[core_id])
+		return;
+
+	LOG_DEBUG("wakeup core %d\n", core_id);
+	apic_send_ipi(core_id, 82+32);
+}
+
 static void apic_err_handler(struct state *s)
 {
 	LOG_ERROR("Got APIC error 0x%x\n", lapic_read(APIC_ESR));
@@ -1091,6 +1109,11 @@ static void apic_shutdown(struct state * s)
 	LOG_DEBUG("Receive shutdown interrupt\n");
 }
 
+static void apic_wakeup_handler(struct state * s)
+{
+	LOG_DEBUG("Receive wakeup interrupt\n");
+}
+
 int apic_init(void)
 {
 	int ret;
@@ -1105,6 +1128,7 @@ int apic_init(void)
 	irq_install_handler(80+32, apic_tlb_handler);
 #endif
 	irq_install_handler(81+32, apic_shutdown);
+	irq_install_handler(82+32, apic_wakeup_handler);
 	if (apic_processors[boot_processor])
 		LOG_INFO("Boot processor %u (ID %u)\n", boot_processor, apic_processors[boot_processor]->id);
 	else
diff --git a/arch/x86/kernel/tasks.c b/arch/x86/kernel/tasks.c
@@ -196,7 +196,7 @@ int create_default_frame(task_t* task, entry_point_t ep, void* arg, uint32_t cor
 void wait_for_task(void)
 {
 	if (!has_mwait()) {
-		PAUSE;
+		HALT;
 	} else {
 		void* queue = get_readyqueue();
 
diff --git a/include/hermit/tasks.h b/include/hermit/tasks.h
@@ -166,6 +166,14 @@ void reschedule(void);
  */
 int wakeup_task(tid_t);
 
+/** @brief Wake up a core_id
+ *
+ * Wakeup core to be sure that
+ * the core isn't in halt state
+ *
+ * @param core_id Specifies the core
+ */
+void wakeup_core(uint32_t core_id);
 
 /** @brief Block current task
  *
diff --git a/kernel/tasks.c b/kernel/tasks.c
@@ -176,6 +176,10 @@ static void readyqueues_push_back(uint32_t core_id, task_t* task)
 
 	// increase the number of ready tasks
 	readyqueues[core_id].nr_tasks++;
+
+	// should we wakeup the core?
+	if (readyqueues[core_id].nr_tasks == 1)
+		wakeup_core(core_id);
 }
 
 
@@ -483,7 +487,7 @@ int clone_task(tid_t* id, entry_point_t ep, void* arg, uint8_t prio)
 			task_table[i].stack = stack;
 			task_table[i].prio = prio;
 			task_table[i].heap = curr_task->heap;
-                        task_table[i].start_tick = get_clock_tick();
+			task_table[i].start_tick = get_clock_tick();
 			task_table[i].last_tsc = 0;
 			task_table[i].parent = curr_task->id;
 			task_table[i].tls_addr = curr_task->tls_addr;
@@ -513,6 +517,9 @@ int clone_task(tid_t* id, entry_point_t ep, void* arg, uint8_t prio)
 				readyqueues[core_id].queue[prio-1].last->next = task_table+i;
 				readyqueues[core_id].queue[prio-1].last = task_table+i;
 			}
+			// should we wakeup the core?
+			if (readyqueues[core_id].nr_tasks == 1)
+				wakeup_core(core_id);
 			spinlock_irqsave_unlock(&readyqueues[core_id].lock);
  			break;
 		}

Original file line number	Diff line number	Diff line change
`@@ -196,7 +196,7 @@ int create_default_frame(task_t* task, entry_point_t ep, void* arg, uint32_t cor`
`196`	`196`	`void wait_for_task(void)`
`197`	`197`	`{`
`198`	`198`	`if (!has_mwait()) {`
`199`		`- PAUSE;`
	`199`	`+ HALT;`
`200`	`200`	`} else {`
`201`	`201`	`void* queue = get_readyqueue();`
`202`	`202`