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Date: Thu, 20 Aug 2009 12:17:39 +0200
From: Jens Axboe <jens.axboe@...cle.com>
To: linux-kernel@...r.kernel.org
Cc: jeff@...zik.org, benh@...nel.crashing.org, htejun@...il.com,
bzolnier@...il.com, alan@...rguk.ukuu.org.uk,
Jens Axboe <jens.axboe@...cle.com>
Subject: [PATCH 2/6] workqueue: add support for lazy workqueues
Lazy workqueues are like normal workqueues, except they don't
start a thread per CPU by default. Instead threads are started
when they are needed, and exit when they have been idle for
some time.
Signed-off-by: Jens Axboe <jens.axboe@...cle.com>
---
include/linux/workqueue.h | 5 ++
kernel/workqueue.c | 152 ++++++++++++++++++++++++++++++++++++++++++---
2 files changed, 147 insertions(+), 10 deletions(-)
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index f14e20e..b2dd267 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -32,6 +32,7 @@ struct work_struct {
#ifdef CONFIG_LOCKDEP
struct lockdep_map lockdep_map;
#endif
+ unsigned int cpu;
};
#define WORK_DATA_INIT() ATOMIC_LONG_INIT(0)
@@ -172,6 +173,7 @@ enum {
WQ_F_SINGLETHREAD = 1,
WQ_F_FREEZABLE = 2,
WQ_F_RT = 4,
+ WQ_F_LAZY = 8,
};
#ifdef CONFIG_LOCKDEP
@@ -198,6 +200,7 @@ enum {
__create_workqueue((name), WQ_F_SINGLETHREAD | WQ_F_FREEZABLE)
#define create_singlethread_workqueue(name) \
__create_workqueue((name), WQ_F_SINGLETHREAD)
+#define create_lazy_workqueue(name) __create_workqueue((name), WQ_F_LAZY)
extern void destroy_workqueue(struct workqueue_struct *wq);
@@ -211,6 +214,8 @@ extern int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
extern void flush_workqueue(struct workqueue_struct *wq);
extern void flush_scheduled_work(void);
+extern void workqueue_set_lazy_timeout(struct workqueue_struct *wq,
+ unsigned long timeout);
extern int schedule_work(struct work_struct *work);
extern int schedule_work_on(int cpu, struct work_struct *work);
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 02ba7c9..d9ccebc 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -61,11 +61,17 @@ struct workqueue_struct {
struct list_head list;
const char *name;
unsigned int flags; /* WQ_F_* flags */
+ unsigned long lazy_timeout;
+ unsigned int core_cpu;
#ifdef CONFIG_LOCKDEP
struct lockdep_map lockdep_map;
#endif
};
+/* Default lazy workqueue timeout */
+#define WQ_DEF_LAZY_TIMEOUT (60 * HZ)
+
+
/* Serializes the accesses to the list of workqueues. */
static DEFINE_SPINLOCK(workqueue_lock);
static LIST_HEAD(workqueues);
@@ -81,6 +87,8 @@ static const struct cpumask *cpu_singlethread_map __read_mostly;
*/
static cpumask_var_t cpu_populated_map __read_mostly;
+static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu);
+
/* If it's single threaded, it isn't in the list of workqueues. */
static inline bool is_wq_single_threaded(struct workqueue_struct *wq)
{
@@ -141,11 +149,29 @@ static void insert_work(struct cpu_workqueue_struct *cwq,
static void __queue_work(struct cpu_workqueue_struct *cwq,
struct work_struct *work)
{
+ struct workqueue_struct *wq = cwq->wq;
unsigned long flags;
- spin_lock_irqsave(&cwq->lock, flags);
- insert_work(cwq, work, &cwq->worklist);
- spin_unlock_irqrestore(&cwq->lock, flags);
+ /*
+ * This is a lazy workqueue and this particular CPU thread has
+ * exited. We can't create it from here, so add this work on our
+ * static thread. It will create this thread and move the work there.
+ */
+ if ((wq->flags & WQ_F_LAZY) && !cwq->thread) {
+ struct cpu_workqueue_struct *__cwq;
+
+ local_irq_save(flags);
+ __cwq = wq_per_cpu(wq, wq->core_cpu);
+ work->cpu = smp_processor_id();
+ spin_lock(&__cwq->lock);
+ insert_work(__cwq, work, &__cwq->worklist);
+ spin_unlock_irqrestore(&__cwq->lock, flags);
+ } else {
+ spin_lock_irqsave(&cwq->lock, flags);
+ work->cpu = smp_processor_id();
+ insert_work(cwq, work, &cwq->worklist);
+ spin_unlock_irqrestore(&cwq->lock, flags);
+ }
}
/**
@@ -259,13 +285,16 @@ int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
}
EXPORT_SYMBOL_GPL(queue_delayed_work_on);
-static void run_workqueue(struct cpu_workqueue_struct *cwq)
+static int run_workqueue(struct cpu_workqueue_struct *cwq)
{
+ int did_work = 0;
+
spin_lock_irq(&cwq->lock);
while (!list_empty(&cwq->worklist)) {
struct work_struct *work = list_entry(cwq->worklist.next,
struct work_struct, entry);
work_func_t f = work->func;
+ int cpu;
#ifdef CONFIG_LOCKDEP
/*
* It is permissible to free the struct work_struct
@@ -280,7 +309,34 @@ static void run_workqueue(struct cpu_workqueue_struct *cwq)
trace_workqueue_execution(cwq->thread, work);
cwq->current_work = work;
list_del_init(cwq->worklist.next);
+ cpu = smp_processor_id();
spin_unlock_irq(&cwq->lock);
+ did_work = 1;
+
+ /*
+ * If work->cpu isn't us, then we need to create the target
+ * workqueue thread (if someone didn't already do that) and
+ * move the work over there.
+ */
+ if ((cwq->wq->flags & WQ_F_LAZY) && work->cpu != cpu) {
+ struct cpu_workqueue_struct *__cwq;
+ struct task_struct *p;
+ int err;
+
+ __cwq = wq_per_cpu(cwq->wq, work->cpu);
+ p = __cwq->thread;
+ if (!p)
+ err = create_workqueue_thread(__cwq, work->cpu);
+ p = __cwq->thread;
+ if (p) {
+ if (work->cpu >= 0)
+ kthread_bind(p, work->cpu);
+ insert_work(__cwq, work, &__cwq->worklist);
+ wake_up_process(p);
+ goto out;
+ }
+ }
+
BUG_ON(get_wq_data(work) != cwq);
work_clear_pending(work);
@@ -305,24 +361,45 @@ static void run_workqueue(struct cpu_workqueue_struct *cwq)
cwq->current_work = NULL;
}
spin_unlock_irq(&cwq->lock);
+out:
+ return did_work;
}
static int worker_thread(void *__cwq)
{
struct cpu_workqueue_struct *cwq = __cwq;
+ struct workqueue_struct *wq = cwq->wq;
+ unsigned long last_active = jiffies;
DEFINE_WAIT(wait);
+ int may_exit;
- if (cwq->wq->flags & WQ_F_FREEZABLE)
+ if (wq->flags & WQ_F_FREEZABLE)
set_freezable();
set_user_nice(current, -5);
+ /*
+ * Allow exit if this isn't our core thread
+ */
+ if ((wq->flags & WQ_F_LAZY) && smp_processor_id() != wq->core_cpu)
+ may_exit = 1;
+ else
+ may_exit = 0;
+
for (;;) {
+ int did_work;
+
prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE);
if (!freezing(current) &&
!kthread_should_stop() &&
- list_empty(&cwq->worklist))
- schedule();
+ list_empty(&cwq->worklist)) {
+ unsigned long timeout = wq->lazy_timeout;
+
+ if (timeout && may_exit)
+ schedule_timeout(timeout);
+ else
+ schedule();
+ }
finish_wait(&cwq->more_work, &wait);
try_to_freeze();
@@ -330,7 +407,19 @@ static int worker_thread(void *__cwq)
if (kthread_should_stop())
break;
- run_workqueue(cwq);
+ did_work = run_workqueue(cwq);
+
+ /*
+ * If we did no work for the defined timeout period and we are
+ * allowed to exit, do so.
+ */
+ if (did_work)
+ last_active = jiffies;
+ else if (time_after(jiffies, last_active + wq->lazy_timeout) &&
+ may_exit) {
+ cwq->thread = NULL;
+ break;
+ }
}
return 0;
@@ -814,7 +903,10 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
cwq = init_cpu_workqueue(wq, singlethread_cpu);
err = create_workqueue_thread(cwq, singlethread_cpu);
start_workqueue_thread(cwq, -1);
+ wq->core_cpu = singlethread_cpu;
} else {
+ int created = 0;
+
cpu_maps_update_begin();
/*
* We must place this wq on list even if the code below fails.
@@ -833,10 +925,16 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
*/
for_each_possible_cpu(cpu) {
cwq = init_cpu_workqueue(wq, cpu);
- if (err || !cpu_online(cpu))
+ if (err || !cpu_online(cpu) ||
+ (created && (wq->flags & WQ_F_LAZY)))
continue;
err = create_workqueue_thread(cwq, cpu);
start_workqueue_thread(cwq, cpu);
+ if (!err) {
+ if (!created)
+ wq->core_cpu = cpu;
+ created++;
+ }
}
cpu_maps_update_done();
}
@@ -844,7 +942,9 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
if (err) {
destroy_workqueue(wq);
wq = NULL;
- }
+ } else if (wq->flags & WQ_F_LAZY)
+ workqueue_set_lazy_timeout(wq, WQ_DEF_LAZY_TIMEOUT);
+
return wq;
}
EXPORT_SYMBOL_GPL(__create_workqueue_key);
@@ -877,6 +977,13 @@ static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq)
cwq->thread = NULL;
}
+static bool hotplug_should_start_thread(struct workqueue_struct *wq, int cpu)
+{
+ if ((wq->flags & WQ_F_LAZY) && cpu != wq->core_cpu)
+ return 0;
+ return 1;
+}
+
/**
* destroy_workqueue - safely terminate a workqueue
* @wq: target workqueue
@@ -923,6 +1030,8 @@ undo:
switch (action) {
case CPU_UP_PREPARE:
+ if (!hotplug_should_start_thread(wq, cpu))
+ break;
if (!create_workqueue_thread(cwq, cpu))
break;
printk(KERN_ERR "workqueue [%s] for %i failed\n",
@@ -932,6 +1041,8 @@ undo:
goto undo;
case CPU_ONLINE:
+ if (!hotplug_should_start_thread(wq, cpu))
+ break;
start_workqueue_thread(cwq, cpu);
break;
@@ -999,6 +1110,27 @@ long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg)
EXPORT_SYMBOL_GPL(work_on_cpu);
#endif /* CONFIG_SMP */
+/**
+ * workqueue_set_lazy_timeout - set lazy exit timeout
+ * @wq: the associated workqueue_struct
+ * @timeout: timeout in jiffies
+ *
+ * This will set the timeout for a lazy workqueue. If no work has been
+ * processed for @timeout jiffies, then the workqueue is allowed to exit.
+ * It will be dynamically created again when work is queued to it.
+ *
+ * Note that this only works for workqueues created with
+ * create_lazy_workqueue().
+ */
+void workqueue_set_lazy_timeout(struct workqueue_struct *wq,
+ unsigned long timeout)
+{
+ if (WARN_ON(!(wq->flags & WQ_F_LAZY)))
+ return;
+
+ wq->lazy_timeout = timeout;
+}
+
void __init init_workqueues(void)
{
alloc_cpumask_var(&cpu_populated_map, GFP_KERNEL);
--
1.6.4.173.g3f189
--
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