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workqueue: prepare for WQ_UNBOUND implementation
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In preparation of WQ_UNBOUND addition, make the following changes.

* Add WORK_CPU_* constants for pseudo cpu id numbers used (currently
  only WORK_CPU_NONE) and use them instead of NR_CPUS.  This is to
  allow another pseudo cpu id for unbound cpu.

* Reorder WQ_* flags.

* Make workqueue_struct->cpu_wq a union which contains a percpu
  pointer, regular pointer and an unsigned long value and use
  kzalloc/kfree() in UP allocation path.  This will be used to
  implement unbound workqueues which will use only one cwq on SMPs.

* Move alloc_cwqs() allocation after initialization of wq fields, so
  that alloc_cwqs() has access to wq->flags.

* Trivial relocation of wq local variables in freeze functions.

These changes don't cause any functional change.

Signed-off-by: Tejun Heo <tj@kernel.org>
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Tejun Heo committed Jul 2, 2010
1 parent ad72cf9 commit bdbc5dd
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Showing 2 changed files with 50 additions and 43 deletions.
10 changes: 7 additions & 3 deletions include/linux/workqueue.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,10 @@ enum {
WORK_NR_COLORS = (1 << WORK_STRUCT_COLOR_BITS) - 1,
WORK_NO_COLOR = WORK_NR_COLORS,

/* special cpu IDs */
WORK_CPU_NONE = NR_CPUS,
WORK_CPU_LAST = WORK_CPU_NONE,

/*
* Reserve 6 bits off of cwq pointer w/ debugobjects turned
* off. This makes cwqs aligned to 64 bytes which isn't too
Expand All @@ -60,7 +64,7 @@ enum {

WORK_STRUCT_FLAG_MASK = (1UL << WORK_STRUCT_FLAG_BITS) - 1,
WORK_STRUCT_WQ_DATA_MASK = ~WORK_STRUCT_FLAG_MASK,
WORK_STRUCT_NO_CPU = NR_CPUS << WORK_STRUCT_FLAG_BITS,
WORK_STRUCT_NO_CPU = WORK_CPU_NONE << WORK_STRUCT_FLAG_BITS,

/* bit mask for work_busy() return values */
WORK_BUSY_PENDING = 1 << 0,
Expand Down Expand Up @@ -227,9 +231,9 @@ static inline unsigned int work_static(struct work_struct *work) { return 0; }
clear_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))

enum {
WQ_FREEZEABLE = 1 << 0, /* freeze during suspend */
WQ_NON_REENTRANT = 1 << 0, /* guarantee non-reentrance */
WQ_SINGLE_CPU = 1 << 1, /* only single cpu at a time */
WQ_NON_REENTRANT = 1 << 2, /* guarantee non-reentrance */
WQ_FREEZEABLE = 1 << 2, /* freeze during suspend */
WQ_RESCUER = 1 << 3, /* has an rescue worker */
WQ_HIGHPRI = 1 << 4, /* high priority */
WQ_CPU_INTENSIVE = 1 << 5, /* cpu instensive workqueue */
Expand Down
83 changes: 43 additions & 40 deletions kernel/workqueue.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -190,7 +190,11 @@ struct wq_flusher {
*/
struct workqueue_struct {
unsigned int flags; /* I: WQ_* flags */
struct cpu_workqueue_struct *cpu_wq; /* I: cwq's */
union {
struct cpu_workqueue_struct __percpu *pcpu;
struct cpu_workqueue_struct *single;
unsigned long v;
} cpu_wq; /* I: cwq's */
struct list_head list; /* W: list of all workqueues */

struct mutex flush_mutex; /* protects wq flushing */
Expand Down Expand Up @@ -362,7 +366,11 @@ static atomic_t *get_gcwq_nr_running(unsigned int cpu)
static struct cpu_workqueue_struct *get_cwq(unsigned int cpu,
struct workqueue_struct *wq)
{
return per_cpu_ptr(wq->cpu_wq, cpu);
#ifndef CONFIG_SMP
return wq->cpu_wq.single;
#else
return per_cpu_ptr(wq->cpu_wq.pcpu, cpu);
#endif
}

static unsigned int work_color_to_flags(int color)
Expand Down Expand Up @@ -442,7 +450,7 @@ static struct global_cwq *get_work_gcwq(struct work_struct *work)
return ((struct cpu_workqueue_struct *)data)->gcwq;

cpu = data >> WORK_STRUCT_FLAG_BITS;
if (cpu == NR_CPUS)
if (cpu == WORK_CPU_NONE)
return NULL;

BUG_ON(cpu >= nr_cpu_ids);
Expand Down Expand Up @@ -846,7 +854,7 @@ static void cwq_unbind_single_cpu(struct cpu_workqueue_struct *cwq)
*/
if (likely(!(gcwq->flags & GCWQ_FREEZING))) {
smp_wmb(); /* paired with cmpxchg() in __queue_work() */
wq->single_cpu = NR_CPUS;
wq->single_cpu = WORK_CPU_NONE;
}
}

Expand Down Expand Up @@ -904,7 +912,7 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
*/
retry:
cpu = wq->single_cpu;
arbitrate = cpu == NR_CPUS;
arbitrate = cpu == WORK_CPU_NONE;
if (arbitrate)
cpu = req_cpu;

Expand All @@ -918,7 +926,7 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
* visible on the new cpu after this point.
*/
if (arbitrate)
cmpxchg(&wq->single_cpu, NR_CPUS, cpu);
cmpxchg(&wq->single_cpu, WORK_CPU_NONE, cpu);

if (unlikely(wq->single_cpu != cpu)) {
spin_unlock_irqrestore(&gcwq->lock, flags);
Expand Down Expand Up @@ -2572,7 +2580,7 @@ int keventd_up(void)
return system_wq != NULL;
}

static struct cpu_workqueue_struct *alloc_cwqs(void)
static int alloc_cwqs(struct workqueue_struct *wq)
{
/*
* cwqs are forced aligned according to WORK_STRUCT_FLAG_BITS.
Expand All @@ -2582,40 +2590,36 @@ static struct cpu_workqueue_struct *alloc_cwqs(void)
const size_t size = sizeof(struct cpu_workqueue_struct);
const size_t align = max_t(size_t, 1 << WORK_STRUCT_FLAG_BITS,
__alignof__(unsigned long long));
struct cpu_workqueue_struct *cwqs;
#ifndef CONFIG_SMP
void *ptr;

/*
* On UP, percpu allocator doesn't honor alignment parameter
* and simply uses arch-dependent default. Allocate enough
* room to align cwq and put an extra pointer at the end
* pointing back to the originally allocated pointer which
* will be used for free.
*
* FIXME: This really belongs to UP percpu code. Update UP
* percpu code to honor alignment and remove this ugliness.
* Allocate enough room to align cwq and put an extra pointer
* at the end pointing back to the originally allocated
* pointer which will be used for free.
*/
ptr = __alloc_percpu(size + align + sizeof(void *), 1);
cwqs = PTR_ALIGN(ptr, align);
*(void **)per_cpu_ptr(cwqs + 1, 0) = ptr;
ptr = kzalloc(size + align + sizeof(void *), GFP_KERNEL);
if (ptr) {
wq->cpu_wq.single = PTR_ALIGN(ptr, align);
*(void **)(wq->cpu_wq.single + 1) = ptr;
}
#else
/* On SMP, percpu allocator can do it itself */
cwqs = __alloc_percpu(size, align);
/* On SMP, percpu allocator can align itself */
wq->cpu_wq.pcpu = __alloc_percpu(size, align);
#endif
/* just in case, make sure it's actually aligned */
BUG_ON(!IS_ALIGNED((unsigned long)cwqs, align));
return cwqs;
BUG_ON(!IS_ALIGNED(wq->cpu_wq.v, align));
return wq->cpu_wq.v ? 0 : -ENOMEM;
}

static void free_cwqs(struct cpu_workqueue_struct *cwqs)
static void free_cwqs(struct workqueue_struct *wq)
{
#ifndef CONFIG_SMP
/* on UP, the pointer to free is stored right after the cwq */
if (cwqs)
free_percpu(*(void **)per_cpu_ptr(cwqs + 1, 0));
if (wq->cpu_wq.single)
kfree(*(void **)(wq->cpu_wq.single + 1));
#else
free_percpu(cwqs);
free_percpu(wq->cpu_wq.pcpu);
#endif
}

Expand Down Expand Up @@ -2645,22 +2649,21 @@ struct workqueue_struct *__alloc_workqueue_key(const char *name,
if (!wq)
goto err;

wq->cpu_wq = alloc_cwqs();
if (!wq->cpu_wq)
goto err;

wq->flags = flags;
wq->saved_max_active = max_active;
mutex_init(&wq->flush_mutex);
atomic_set(&wq->nr_cwqs_to_flush, 0);
INIT_LIST_HEAD(&wq->flusher_queue);
INIT_LIST_HEAD(&wq->flusher_overflow);
wq->single_cpu = NR_CPUS;
wq->single_cpu = WORK_CPU_NONE;

wq->name = name;
lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);
INIT_LIST_HEAD(&wq->list);

if (alloc_cwqs(wq) < 0)
goto err;

for_each_possible_cpu(cpu) {
struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
struct global_cwq *gcwq = get_gcwq(cpu);
Expand Down Expand Up @@ -2710,7 +2713,7 @@ struct workqueue_struct *__alloc_workqueue_key(const char *name,
return wq;
err:
if (wq) {
free_cwqs(wq->cpu_wq);
free_cwqs(wq);
free_cpumask_var(wq->mayday_mask);
kfree(wq->rescuer);
kfree(wq);
Expand Down Expand Up @@ -2755,7 +2758,7 @@ void destroy_workqueue(struct workqueue_struct *wq)
free_cpumask_var(wq->mayday_mask);
}

free_cwqs(wq->cpu_wq);
free_cwqs(wq);
kfree(wq);
}
EXPORT_SYMBOL_GPL(destroy_workqueue);
Expand Down Expand Up @@ -2821,13 +2824,13 @@ EXPORT_SYMBOL_GPL(workqueue_congested);
* @work: the work of interest
*
* RETURNS:
* CPU number if @work was ever queued. NR_CPUS otherwise.
* CPU number if @work was ever queued. WORK_CPU_NONE otherwise.
*/
unsigned int work_cpu(struct work_struct *work)
{
struct global_cwq *gcwq = get_work_gcwq(work);

return gcwq ? gcwq->cpu : NR_CPUS;
return gcwq ? gcwq->cpu : WORK_CPU_NONE;
}
EXPORT_SYMBOL_GPL(work_cpu);

Expand Down Expand Up @@ -3300,7 +3303,6 @@ EXPORT_SYMBOL_GPL(work_on_cpu);
*/
void freeze_workqueues_begin(void)
{
struct workqueue_struct *wq;
unsigned int cpu;

spin_lock(&workqueue_lock);
Expand All @@ -3310,6 +3312,7 @@ void freeze_workqueues_begin(void)

for_each_possible_cpu(cpu) {
struct global_cwq *gcwq = get_gcwq(cpu);
struct workqueue_struct *wq;

spin_lock_irq(&gcwq->lock);

Expand Down Expand Up @@ -3344,7 +3347,6 @@ void freeze_workqueues_begin(void)
*/
bool freeze_workqueues_busy(void)
{
struct workqueue_struct *wq;
unsigned int cpu;
bool busy = false;

Expand All @@ -3353,6 +3355,7 @@ bool freeze_workqueues_busy(void)
BUG_ON(!workqueue_freezing);

for_each_possible_cpu(cpu) {
struct workqueue_struct *wq;
/*
* nr_active is monotonically decreasing. It's safe
* to peek without lock.
Expand Down Expand Up @@ -3386,7 +3389,6 @@ bool freeze_workqueues_busy(void)
*/
void thaw_workqueues(void)
{
struct workqueue_struct *wq;
unsigned int cpu;

spin_lock(&workqueue_lock);
Expand All @@ -3396,6 +3398,7 @@ void thaw_workqueues(void)

for_each_possible_cpu(cpu) {
struct global_cwq *gcwq = get_gcwq(cpu);
struct workqueue_struct *wq;

spin_lock_irq(&gcwq->lock);

Expand Down Expand Up @@ -3443,7 +3446,7 @@ void __init init_workqueues(void)
* sure cpu number won't overflow into kernel pointer area so
* that they can be distinguished.
*/
BUILD_BUG_ON(NR_CPUS << WORK_STRUCT_FLAG_BITS >= PAGE_OFFSET);
BUILD_BUG_ON(WORK_CPU_LAST << WORK_STRUCT_FLAG_BITS >= PAGE_OFFSET);

hotcpu_notifier(workqueue_cpu_callback, CPU_PRI_WORKQUEUE);

Expand Down

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