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Subject[PATCH] RT: Add priority-queuing and priority-inheritance to workqueue infrastructure
Date
The following workqueue related patch is a port of the original VFCIPI PI
patch I submitted earlier. There is still more work to be done to add the
"schedule_on_cpu()" type behavior, and even more if we want to use this as
part of KVM. But for now, this patch can stand alone so I thought I would
get it out there.

------------------------------------------------------------------

Mainline workqueues treat all requests the same. This patch prioritizes
requests in the queue based on the callers current rt_priority. It also
adds a priority-inheritance feature to avoid inversion.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
---

include/linux/workqueue.h | 2
kernel/workqueue.c | 198 +++++++++++++++++++++++++++++++++------------
2 files changed, 149 insertions(+), 51 deletions(-)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 925d898..ae740b6 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -28,6 +28,7 @@ struct work_struct {
#define WORK_STRUCT_WQ_DATA_MASK (~WORK_STRUCT_FLAG_MASK)
struct list_head entry;
work_func_t func;
+ int prio;
};

#define WORK_DATA_INIT() ATOMIC_LONG_INIT(0)
@@ -81,6 +82,7 @@ struct execute_work {
(_work)->data = (atomic_long_t) WORK_DATA_INIT(); \
INIT_LIST_HEAD(&(_work)->entry); \
PREPARE_WORK((_work), (_func)); \
+ (_work)->prio = -1; \
} while (0)

#define INIT_DELAYED_WORK(_work, _func) \
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index e339c80..ecd5e01 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -14,6 +14,8 @@
* Theodore Ts'o <tytso@mit.edu>
*
* Made to use alloc_percpu by Christoph Lameter <clameter@sgi.com>.
+ *
+ * RT-queues and PI by Gregory Haskins <ghaskins@novell.com>
*/

#include <linux/module.h>
@@ -36,6 +38,13 @@

#include <asm/uaccess.h>

+/* Note: prio_array inspiration credit goes to the RT scheduler...*/
+struct prio_array {
+ DECLARE_BITMAP(bitmap, MAX_RT_PRIO+1); /* +1 bit for delimiter */
+ unsigned long count;
+ struct list_head queue[MAX_RT_PRIO];
+};
+
/*
* The per-CPU workqueue (if single thread, we always use the first
* possible cpu).
@@ -45,6 +54,7 @@ struct cpu_workqueue_struct {
spinlock_t lock;

struct list_head worklist;
+ struct prio_array rt_worklist;
wait_queue_head_t more_work;
struct work_struct *current_work;

@@ -52,6 +62,7 @@ struct cpu_workqueue_struct {
struct task_struct *thread;

int run_depth; /* Detect run_workqueue() recursion depth */
+ int prio; /* -1 = normal priority, 0-99 = RT priority */
} ____cacheline_aligned;

/*
@@ -82,6 +93,94 @@ static cpumask_t cpu_singlethread_map __read_mostly;
*/
static cpumask_t cpu_populated_map __read_mostly;

+/*
+ * ----------------------------------------
+ * prio_array
+ * ----------------------------------------
+ */
+static void prio_array_init(struct prio_array *array)
+{
+ int i;
+
+ memset(array->bitmap, 0, sizeof(array->bitmap));
+ array->count = 0;
+
+ for (i=0; i<MAX_RT_PRIO; i++)
+ INIT_LIST_HEAD(&array->queue[i]);
+}
+
+static struct work_struct* prio_array_dequeue(struct prio_array *array)
+{
+ struct list_head *head;
+ struct work_struct *work;
+ int idx;
+
+ if (!array->count)
+ return NULL;
+
+ idx = sched_find_first_bit(array->bitmap);
+
+ head = array->queue + idx;
+
+ /* If we got here, there better be something in the list */
+ BUG_ON(!head);
+ BUG_ON(list_empty(head));
+
+ work = list_first_entry(head, struct work_struct, entry);
+ BUG_ON(!work);
+
+ list_del_init(&work->entry);
+ array->count--;
+
+ if (list_empty(head))
+ __clear_bit(idx, &array->bitmap);
+
+ return work;
+}
+
+static void prio_array_enqueue(struct prio_array *array,
+ struct work_struct *work,
+ int prio, int tail)
+{
+ struct list_head *head;
+
+ BUG_ON(prio < 0);
+ BUG_ON(prio > MAX_RT_PRIO);
+
+ head = array->queue + prio;
+
+ if (tail)
+ list_add_tail(&work->entry, head);
+ else
+ list_add(&work->entry, head);
+
+ __set_bit(prio, &array->bitmap);
+ array->count++;
+}
+
+#define CWQ_DEFAULT_PRIO 1
+
+/* Assumes lock is held */
+static void wq_task_setprio(struct cpu_workqueue_struct *cwq, int prio)
+{
+ struct sched_param param = { 0, };
+ pid_t pid = cwq->thread->pid;
+
+ if (prio < CWQ_DEFAULT_PRIO)
+ prio = CWQ_DEFAULT_PRIO;
+
+ if (cwq->prio != prio) {
+ if (prio != -1) {
+ param.sched_priority = prio;
+ sys_sched_setscheduler(pid, SCHED_FIFO, &param);
+ } else {
+ sys_sched_setscheduler(pid, SCHED_NORMAL, &param);
+ }
+
+ cwq->prio = prio;
+ }
+}
+
/* If it's single threaded, it isn't in the list of workqueues. */
static inline int is_single_threaded(struct workqueue_struct *wq)
{
@@ -133,10 +232,22 @@ static void insert_work(struct cpu_workqueue_struct *cwq,
* 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);
+ if (rt_task(current)) {
+ work->prio = current->rt_priority;
+ prio_array_enqueue(&cwq->rt_worklist, work, work->prio, tail);
+
+ /* Priority inheritance on the kthread */
+ if (cwq->prio < work->prio)
+ wq_task_setprio(cwq, work->prio);
+ } else {
+ work->prio = -1;
+ if (tail)
+ list_add_tail(&work->entry, &cwq->worklist);
+ else
+ list_add(&work->entry, &cwq->worklist);
+
+ }
+
wake_up(&cwq->more_work);
}

@@ -254,8 +365,30 @@ static void leak_check(void *func)
dump_stack();
}

+static struct work_struct* cwq_dequeue(struct cpu_workqueue_struct *cwq)
+{
+ struct work_struct *work;
+
+ /* First check the RT items */
+ work = prio_array_dequeue(&cwq->rt_worklist);
+ if (!work) {
+ /* If nothing is found there, check the normal queue */
+ if (!list_empty(&cwq->worklist)) {
+ work = list_first_entry(&cwq->worklist,
+ struct work_struct,
+ entry);
+ BUG_ON(!work);
+ list_del_init(&work->entry);
+ }
+ }
+
+ return work;
+}
+
static void run_workqueue(struct cpu_workqueue_struct *cwq)
{
+ struct work_struct *work;
+
spin_lock_irq(&cwq->lock);
cwq->run_depth++;
if (cwq->run_depth > 3) {
@@ -264,13 +397,12 @@ static void run_workqueue(struct cpu_workqueue_struct *cwq)
__FUNCTION__, cwq->run_depth);
dump_stack();
}
- while (!list_empty(&cwq->worklist)) {
- struct work_struct *work = list_entry(cwq->worklist.next,
- struct work_struct, entry);
+ while ((work = cwq_dequeue(cwq))) {
work_func_t f = work->func;

+ wq_task_setprio(cwq, work->prio);
cwq->current_work = work;
- list_del_init(cwq->worklist.next);
+
spin_unlock_irq(&cwq->lock);

BUG_ON(get_wq_data(work) != cwq);
@@ -283,6 +415,10 @@ static void run_workqueue(struct cpu_workqueue_struct *cwq)
spin_lock_irq(&cwq->lock);
cwq->current_work = NULL;
}
+
+ /* Make sure we are back to normal priority before sleeping */
+ wq_task_setprio(cwq, -1);
+
cwq->run_depth--;
spin_unlock_irq(&cwq->lock);
}
@@ -295,7 +431,7 @@ static int worker_thread(void *__cwq)
if (!cwq->wq->freezeable)
current->flags |= PF_NOFREEZE;

- set_user_nice(current, -5);
+ wq_task_setprio(cwq, -1);

for (;;) {
prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE);
@@ -691,7 +827,9 @@ init_cpu_workqueue(struct workqueue_struct *wq, int cpu)
cwq->wq = wq;
spin_lock_init(&cwq->lock);
INIT_LIST_HEAD(&cwq->worklist);
+ prio_array_init(&cwq->rt_worklist);
init_waitqueue_head(&cwq->more_work);
+ cwq->prio = -1;

return cwq;
}
@@ -803,47 +941,6 @@ static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
cwq->thread = NULL;
}

-void set_workqueue_thread_prio(struct workqueue_struct *wq, int cpu,
- int policy, int rt_priority, int nice)
-{
- struct sched_param param = { .sched_priority = rt_priority };
- struct cpu_workqueue_struct *cwq;
- mm_segment_t oldfs = get_fs();
- struct task_struct *p;
- unsigned long flags;
- int ret;
-
- cwq = per_cpu_ptr(wq->cpu_wq, cpu);
- spin_lock_irqsave(&cwq->lock, flags);
- p = cwq->thread;
- spin_unlock_irqrestore(&cwq->lock, flags);
-
- set_user_nice(p, nice);
-
- set_fs(KERNEL_DS);
- ret = sys_sched_setscheduler(p->pid, policy, &param);
- set_fs(oldfs);
-
- WARN_ON(ret);
-}
-
- void set_workqueue_prio(struct workqueue_struct *wq, int policy,
- int rt_priority, int nice)
-{
- int cpu;
-
- /* We don't need the distraction of CPUs appearing and vanishing. */
- mutex_lock(&workqueue_mutex);
- if (is_single_threaded(wq))
- set_workqueue_thread_prio(wq, 0, policy, rt_priority, nice);
- else {
- for_each_online_cpu(cpu)
- set_workqueue_thread_prio(wq, cpu, policy,
- rt_priority, nice);
- }
- mutex_unlock(&workqueue_mutex);
-}
-
/**
* destroy_workqueue - safely terminate a workqueue
* @wq: target workqueue
@@ -926,5 +1023,4 @@ void __init init_workqueues(void)
hotcpu_notifier(workqueue_cpu_callback, 0);
keventd_wq = create_workqueue("events");
BUG_ON(!keventd_wq);
- set_workqueue_prio(keventd_wq, SCHED_FIFO, 1, -20);
}
-
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