From 068fbf2cb6c9211e90a989ae918eb69bc537c96f Mon Sep 17 00:00:00 2001
From: Stefan Lankes <slankes@eonerc.rwth-aachen.de>
Date: Sun, 6 Nov 2016 19:26:19 +0100
Subject: [PATCH] use mwait to check the readyqueue for new arriving tasks

---
 hermit/arch/x86/kernel/tasks.c | 15 +++++++++++++++
 hermit/include/hermit/tasks.h  | 11 +++++++++++
 hermit/kernel/main.c           | 12 ++----------
 hermit/kernel/syscall.c        |  3 ---
 hermit/kernel/tasks.c          |  6 ++++++
 5 files changed, 34 insertions(+), 13 deletions(-)

diff --git a/hermit/arch/x86/kernel/tasks.c b/hermit/arch/x86/kernel/tasks.c
index 2c40cc343..759753ec5 100644
--- a/hermit/arch/x86/kernel/tasks.c
+++ b/hermit/arch/x86/kernel/tasks.c
@@ -136,3 +136,18 @@ int create_default_frame(task_t* task, entry_point_t ep, void* arg, uint32_t cor
 
 	return 0;
 }
+
+void wait_for_task(void)
+{
+	if (!has_mwait()) {
+		PAUSE;
+	} else {
+		void* queue = get_readyqueue();
+
+		if (has_clflush())
+			clflush(queue);
+
+		monitor(queue, 0, 0);
+		mwait(0xF /* = c0 */, 1 /* break on interrupt flag */);
+	}
+}
diff --git a/hermit/include/hermit/tasks.h b/hermit/include/hermit/tasks.h
index 05d3dcbac..553021618 100644
--- a/hermit/include/hermit/tasks.h
+++ b/hermit/include/hermit/tasks.h
@@ -187,6 +187,17 @@ int wakeup_task(tid_t);
  */
 int block_current_task(void);
 
+/** @brief Block task until a new arrived
+ *
+ */
+void wait_for_task(void);
+
+/** @brief Get readyqueue of the current core
+ *
+ * @return
+ *  - address of the readyqueue
+ */ 
+void* get_readyqueue(void);
 
 /** @brief Get a process control block
  *
diff --git a/hermit/kernel/main.c b/hermit/kernel/main.c
index dfd494e4d..160cd2f20 100644
--- a/hermit/kernel/main.c
+++ b/hermit/kernel/main.c
@@ -95,8 +95,6 @@ extern int32_t possible_isles;
 extern uint32_t boot_processor;
 extern volatile int libc_sd;
 
-uint32_t idle_poll = 1;
-
 islelock_t* rcce_lock = NULL;
 rcce_mpb_t* rcce_mpb = NULL;
 
@@ -307,10 +305,7 @@ int smp_main(void)
 
 	while(1) {
 		check_workqueues();
-		if (idle_poll)
-			PAUSE;
-		else
-			HALT;
+		wait_for_task();
 	}
 
 	return 0;
@@ -615,10 +610,7 @@ int hermit_main(void)
 
 	while(1) {
 		check_workqueues();
-		if (idle_poll)
-			PAUSE;
-		else
-			HALT;
+		wait_for_task();
 	}
 
 	return 0;
diff --git a/hermit/kernel/syscall.c b/hermit/kernel/syscall.c
index 4f110f682..33e567081 100644
--- a/hermit/kernel/syscall.c
+++ b/hermit/kernel/syscall.c
@@ -50,7 +50,6 @@ extern spinlock_irqsave_t stdio_lock;
 extern int32_t isle;
 extern int32_t possible_isles;
 extern volatile int libc_sd;
-extern uint32_t idle_poll;
 
 tid_t sys_getpid(void)
 {
@@ -99,9 +98,7 @@ void NORETURN sys_exit(int arg)
 		reschedule();
 
 		lwip_close(s);
-		idle_poll = 0;
 	} else {
-		idle_poll = 0;
 		spinlock_irqsave_unlock(&lwip_lock);
 	}
 
diff --git a/hermit/kernel/tasks.c b/hermit/kernel/tasks.c
index 7f87c59aa..982d7e9c7 100644
--- a/hermit/kernel/tasks.c
+++ b/hermit/kernel/tasks.c
@@ -232,6 +232,12 @@ uint32_t get_highest_priority(void)
 }
 
 
+void* get_readyqueue(void)
+{
+	return &readyqueues[CORE_ID];
+}
+
+
 int multitasking_init(void)
 {
 	uint32_t core_id = CORE_ID;