[RFC/PATCH 4/5] rt: PI-workqueue support

[Peter Zijlstra]

Add support for priority queueing and priority inheritance to the workqueue
infrastructure. This is done by replacing the linear linked worklist with a
priority sorted plist.

The drawback is that this breaks the workqueue barrier, needed to support
flush_workqueue() and wait_on_work().

Signed-off-by: Daniel Walker <dwalker@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
---
 include/linux/workqueue.h |    7 ++++---
 kernel/power/poweroff.c   |    1 +
 kernel/workqueue.c        |   40 +++++++++++++++++++++++++---------------
 3 files changed, 30 insertions(+), 18 deletions(-)

Index: linux-2.6/include/linux/workqueue.h
===================================================================
--- linux-2.6.orig/include/linux/workqueue.h
+++ linux-2.6/include/linux/workqueue.h
@@ -8,6 +8,7 @@
 #include <linux/timer.h>
 #include <linux/linkage.h>
 #include <linux/bitops.h>
+#include <linux/plist.h>
 #include <asm/atomic.h>
 
 struct workqueue_struct;
@@ -26,7 +27,7 @@ struct work_struct {
 #define WORK_STRUCT_PENDING 0		/* T if work item pending execution */
 #define WORK_STRUCT_FLAG_MASK (3UL)
 #define WORK_STRUCT_WQ_DATA_MASK (~WORK_STRUCT_FLAG_MASK)
-	struct list_head entry;
+	struct plist_node entry;
 	work_func_t func;
 };
 
@@ -43,7 +44,7 @@ struct execute_work {
 
 #define __WORK_INITIALIZER(n, f) {				\
 	.data = WORK_DATA_INIT(),				\
-	.entry	= { &(n).entry, &(n).entry },			\
+	.entry	= PLIST_NODE_INIT(n.entry, MAX_PRIO),		\
 	.func = (f),						\
 	}
 
@@ -79,7 +80,7 @@ struct execute_work {
 #define INIT_WORK(_work, _func)						\
 	do {								\
 		(_work)->data = (atomic_long_t) WORK_DATA_INIT();	\
-		INIT_LIST_HEAD(&(_work)->entry);			\
+		plist_node_init(&(_work)->entry, -1);			\
 		PREPARE_WORK((_work), (_func));				\
 	} while (0)
 
Index: linux-2.6/kernel/power/poweroff.c
===================================================================
--- linux-2.6.orig/kernel/power/poweroff.c
+++ linux-2.6/kernel/power/poweroff.c
@@ -8,6 +8,7 @@
 #include <linux/sysrq.h>
 #include <linux/init.h>
 #include <linux/pm.h>
+#include <linux/sched.h>
 #include <linux/workqueue.h>
 #include <linux/reboot.h>
 
Index: linux-2.6/kernel/workqueue.c
===================================================================
--- linux-2.6.orig/kernel/workqueue.c
+++ linux-2.6/kernel/workqueue.c
@@ -44,7 +44,7 @@ struct cpu_workqueue_struct {
 
 	spinlock_t lock;
 
-	struct list_head worklist;
+	struct plist_head worklist;
 	wait_queue_head_t more_work;
 	struct work_struct *current_work;
 
@@ -127,16 +127,19 @@ struct cpu_workqueue_struct *get_wq_data
 static void insert_work(struct cpu_workqueue_struct *cwq,
 				struct work_struct *work, int tail)
 {
+	int prio = current->normal_prio;
+
 	set_wq_data(work, cwq);
 	/*
 	 * Ensure that we get the right work->data if we see the
 	 * result of list_add() below, see try_to_grab_pending().
 	 */
 	smp_wmb();
-	if (tail)
-		list_add_tail(&work->entry, &cwq->worklist);
-	else
-		list_add(&work->entry, &cwq->worklist);
+	plist_node_init(&work->entry, prio);
+	plist_add(&work->entry, &cwq->worklist);
+
+	if (prio < cwq->thread->prio)
+		task_setprio(cwq->thread, prio);
 	wake_up(&cwq->more_work);
 }
 
@@ -168,7 +171,7 @@ int fastcall queue_work(struct workqueue
 	int ret = 0, cpu = raw_smp_processor_id();
 
 	if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
-		BUG_ON(!list_empty(&work->entry));
+		BUG_ON(!plist_node_empty(&work->entry));
 		__queue_work(wq_per_cpu(wq, cpu), work);
 		ret = 1;
 	}
@@ -222,7 +225,7 @@ int queue_delayed_work_on(int cpu, struc
 
 	if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
 		BUG_ON(timer_pending(timer));
-		BUG_ON(!list_empty(&work->entry));
+		BUG_ON(!plist_node_empty(&work->entry));
 
 		/* This stores cwq for the moment, for the timer_fn */
 		set_wq_data(work, wq_per_cpu(wq, raw_smp_processor_id()));
@@ -264,13 +267,17 @@ static void run_workqueue(struct cpu_wor
 			__FUNCTION__, cwq->run_depth);
 		dump_stack();
 	}
-	while (!list_empty(&cwq->worklist)) {
-		struct work_struct *work = list_entry(cwq->worklist.next,
+	while (!plist_head_empty(&cwq->worklist)) {
+		struct work_struct *work = plist_first_entry(&cwq->worklist,
 						struct work_struct, entry);
 		work_func_t f = work->func;
 
+		if (likely(cwq->thread->prio != work->entry.prio))
+			task_setprio(cwq->thread, work->entry.prio);
+
 		cwq->current_work = work;
-		list_del_init(cwq->worklist.next);
+		plist_del(&work->entry, &cwq->worklist);
+		plist_node_init(&work->entry, MAX_PRIO);
 		spin_unlock_irq(&cwq->lock);
 
 		BUG_ON(get_wq_data(work) != cwq);
@@ -283,6 +290,7 @@ static void run_workqueue(struct cpu_wor
 		spin_lock_irq(&cwq->lock);
 		cwq->current_work = NULL;
 	}
+	task_setprio(cwq->thread, current->normal_prio);
 	cwq->run_depth--;
 	spin_unlock_irq(&cwq->lock);
 }
@@ -301,7 +309,7 @@ static int worker_thread(void *__cwq)
 		prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE);
 		if (!freezing(current) &&
 		    !kthread_should_stop() &&
-		    list_empty(&cwq->worklist))
+		    plist_head_empty(&cwq->worklist))
 			schedule();
 		finish_wait(&cwq->more_work, &wait);
 
@@ -354,7 +362,8 @@ static int flush_cpu_workqueue(struct cp
 
 		active = 0;
 		spin_lock_irq(&cwq->lock);
-		if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) {
+		if (!plist_head_empty(&cwq->worklist) ||
+			cwq->current_work != NULL) {
 			insert_wq_barrier(cwq, &barr, 1);
 			active = 1;
 		}
@@ -413,7 +422,7 @@ static int try_to_grab_pending(struct wo
 		return ret;
 
 	spin_lock_irq(&cwq->lock);
-	if (!list_empty(&work->entry)) {
+	if (!plist_node_empty(&work->entry)) {
 		/*
 		 * This work is queued, but perhaps we locked the wrong cwq.
 		 * In that case we must see the new value after rmb(), see
@@ -421,7 +430,8 @@ static int try_to_grab_pending(struct wo
 		 */
 		smp_rmb();
 		if (cwq == get_wq_data(work)) {
-			list_del_init(&work->entry);
+			plist_del(&work->entry, &cwq->worklist);
+			plist_node_init(&work->entry, MAX_PRIO);
 			ret = 1;
 		}
 	}
@@ -747,7 +757,7 @@ init_cpu_workqueue(struct workqueue_stru
 
 	cwq->wq = wq;
 	spin_lock_init(&cwq->lock);
-	INIT_LIST_HEAD(&cwq->worklist);
+	plist_head_init(&cwq->worklist, NULL);
 	init_waitqueue_head(&cwq->more_work);
 
 	return cwq;

--

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