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Subject[RFC/PATCH 4/5] rt: PI-workqueue support
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@mvista.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
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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