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Subject[PATCH 3/4] WorkStruct: Merge the pending bit into the wq_data pointer
Date
Reclaim a word from the size of the work_struct by folding the pending bit and
the wq_data pointer together. This shouldn't cause misalignment problems as
all pointers should be at least 4-byte aligned.

Signed-Off-By: David Howells <dhowells@redhat.com>
---
drivers/block/floppy.c | 4 ++--
include/linux/workqueue.h | 19 +++++++++++++++----
kernel/workqueue.c | 41 ++++++++++++++++++++++++++++++++---------
3 files changed, 49 insertions(+), 15 deletions(-)
diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index 5a14fac..aa1eb44 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -1868,7 +1868,7 @@ #endif
printk("fdc_busy=%lu\n", fdc_busy);
if (do_floppy)
printk("do_floppy=%p\n", do_floppy);
- if (floppy_work.pending)
+ if (work_pending(&floppy_work))
printk("floppy_work.func=%p\n", floppy_work.func);
if (timer_pending(&fd_timer))
printk("fd_timer.function=%p\n", fd_timer.function);
@@ -4498,7 +4498,7 @@ #endif
printk("floppy timer still active:%s\n", timeout_message);
if (timer_pending(&fd_timer))
printk("auxiliary floppy timer still active\n");
- if (floppy_work.pending)
+ if (work_pending(&floppy_work))
printk("work still pending\n");
#endif
old_fdc = fdc;
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 0d5bbd4..67e6a7f 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -14,11 +14,15 @@ struct workqueue_struct;
typedef void (*work_func_t)(void *data);

struct work_struct {
- unsigned long pending;
+ /* the first word is the work queue pointer and the pending flag
+ * rolled into one */
+ unsigned long management;
+#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;
work_func_t func;
void *data;
- void *wq_data;
};

struct dwork_struct {
@@ -65,7 +69,7 @@ #define PREPARE_DELAYABLE_WORK(_work, _f
#define INIT_WORK(_work, _func, _data) \
do { \
INIT_LIST_HEAD(&(_work)->entry); \
- (_work)->pending = 0; \
+ (_work)->management = 0; \
PREPARE_WORK((_work), (_func), (_data)); \
} while (0)

@@ -75,6 +79,13 @@ #define INIT_DELAYABLE_WORK(_work, _func
init_timer(&(_work)->timer); \
} while (0)

+/**
+ * work_pending - Find out whether a work item is currently pending
+ * @work: The work item in question
+ */
+#define work_pending(work) \
+ test_bit(WORK_STRUCT_PENDING, &(work)->management)
+
extern struct workqueue_struct *__create_workqueue(const char *name,
int singlethread);
#define create_workqueue(name) __create_workqueue((name), 0)
@@ -124,7 +135,7 @@ static inline int cancel_delayed_work(st

ret = del_timer_sync(&dwork->timer);
if (ret)
- clear_bit(0, &dwork->work.pending);
+ clear_bit(WORK_STRUCT_PENDING, &dwork->work.management);
return ret;
}

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index bb2b6a7..a81d151 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -80,6 +80,29 @@ static inline int is_single_threaded(str
return list_empty(&wq->list);
}

+static inline void set_wq_data(struct work_struct *work, void *wq)
+{
+ unsigned long new, old, res;
+
+ /* assume the pending flag is already set and that the task has already
+ * been queued on this workqueue */
+ new = (unsigned long) wq | (1UL << WORK_STRUCT_PENDING);
+ res = work->management;
+ if (res != new) {
+ do {
+ old = res;
+ new = (unsigned long) wq;
+ new |= (old & WORK_STRUCT_FLAG_MASK);
+ res = cmpxchg(&work->management, old, new);
+ } while (res != old);
+ }
+}
+
+static inline void *get_wq_data(struct work_struct *work)
+{
+ return (void *) (work->management & WORK_STRUCT_WQ_DATA_MASK);
+}
+
/* Preempt must be disabled. */
static void __queue_work(struct cpu_workqueue_struct *cwq,
struct work_struct *work)
@@ -87,7 +110,7 @@ static void __queue_work(struct cpu_work
unsigned long flags;

spin_lock_irqsave(&cwq->lock, flags);
- work->wq_data = cwq;
+ set_wq_data(work, cwq);
list_add_tail(&work->entry, &cwq->worklist);
cwq->insert_sequence++;
wake_up(&cwq->more_work);
@@ -108,7 +131,7 @@ int fastcall queue_work(struct workqueue
{
int ret = 0, cpu = get_cpu();

- if (!test_and_set_bit(0, &work->pending)) {
+ if (!test_and_set_bit(WORK_STRUCT_PENDING, &work->management)) {
if (unlikely(is_single_threaded(wq)))
cpu = singlethread_cpu;
BUG_ON(!list_empty(&work->entry));
@@ -123,7 +146,7 @@ EXPORT_SYMBOL_GPL(queue_work);
static void delayed_work_timer_fn(unsigned long __data)
{
struct dwork_struct *dwork = (struct dwork_struct *)__data;
- struct workqueue_struct *wq = dwork->work.wq_data;
+ struct workqueue_struct *wq = get_wq_data(&dwork->work);
int cpu = smp_processor_id();

if (unlikely(is_single_threaded(wq)))
@@ -147,12 +170,12 @@ int fastcall queue_delayed_work(struct w
struct timer_list *timer = &dwork->timer;
struct work_struct *work = &dwork->work;

- if (!test_and_set_bit(0, &work->pending)) {
+ if (!test_and_set_bit(WORK_STRUCT_PENDING, &work->management)) {
BUG_ON(timer_pending(timer));
BUG_ON(!list_empty(&work->entry));

/* This stores wq for the moment, for the timer_fn */
- work->wq_data = wq;
+ set_wq_data(work, wq);
timer->expires = jiffies + delay;
timer->data = (unsigned long)dwork;
timer->function = delayed_work_timer_fn;
@@ -179,12 +202,12 @@ int queue_delayed_work_on(int cpu, struc
struct timer_list *timer = &dwork->timer;
struct work_struct *work = &dwork->work;

- if (!test_and_set_bit(0, &work->pending)) {
+ if (!test_and_set_bit(WORK_STRUCT_PENDING, &work->management)) {
BUG_ON(timer_pending(timer));
BUG_ON(!list_empty(&work->entry));

/* This stores wq for the moment, for the timer_fn */
- work->wq_data = wq;
+ set_wq_data(work, wq);
timer->expires = jiffies + delay;
timer->data = (unsigned long)dwork;
timer->function = delayed_work_timer_fn;
@@ -220,8 +243,8 @@ static void run_workqueue(struct cpu_wor
list_del_init(cwq->worklist.next);
spin_unlock_irqrestore(&cwq->lock, flags);

- BUG_ON(work->wq_data != cwq);
- clear_bit(0, &work->pending);
+ BUG_ON(get_wq_data(work) != cwq);
+ clear_bit(WORK_STRUCT_PENDING, &work->management);
f(data);

spin_lock_irqsave(&cwq->lock, flags);
-
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