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workqueue: implement attribute-based unbound worker_pool management

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This patch makes unbound worker_pools reference counted and
dynamically created and destroyed as workqueues needing them come and
go.  All unbound worker_pools are hashed on unbound_pool_hash which is
keyed by the content of worker_pool->attrs.

When an unbound workqueue is allocated, get_unbound_pool() is called
with the attributes of the workqueue.  If there already is a matching
worker_pool, the reference count is bumped and the pool is returned.
If not, a new worker_pool with matching attributes is created and
returned.

When an unbound workqueue is destroyed, put_unbound_pool() is called
which decrements the reference count of the associated worker_pool.
If the refcnt reaches zero, the worker_pool is destroyed in sched-RCU
safe way.

Note that the standard unbound worker_pools - normal and highpri ones
with no specific cpumask affinity - are no longer created explicitly
during init_workqueues().  init_workqueues() only initializes
workqueue_attrs to be used for standard unbound pools -
unbound_std_wq_attrs[].  The pools are spawned on demand as workqueues
are created.

v2: - Comment added to init_worker_pool() explaining that @pool should
      be in a condition which can be passed to put_unbound_pool() even
      on failure.

    - pool->refcnt reaching zero and the pool being removed from
      unbound_pool_hash should be dynamic.  pool->refcnt is converted
      to int from atomic_t and now manipulated inside workqueue_lock.

    - Removed an incorrect sanity check on nr_idle in
      put_unbound_pool() which may trigger spuriously.

    All changes were suggested by Lai Jiangshan.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
This commit is contained in:
Tejun Heo 2013-03-12 11:30:03 -07:00
parent 7a4e344c56
commit 29c91e9912
1 changed files with 224 additions and 13 deletions
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237
kernel/workqueue.c
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@ -41,6 +41,7 @@
#include <linux/debug_locks.h>
#include <linux/lockdep.h>
#include <linux/idr.h>
#include <linux/jhash.h>
#include <linux/hashtable.h>
#include <linux/rculist.h>
@ -80,6 +81,7 @@ enum {
NR_STD_WORKER_POOLS = 2, /* # standard pools per cpu */
UNBOUND_POOL_HASH_ORDER = 6, /* hashed by pool->attrs */
BUSY_WORKER_HASH_ORDER = 6, /* 64 pointers */
MAX_IDLE_WORKERS_RATIO = 4, /* 1/4 of busy can be idle */
@ -149,6 +151,8 @@ struct worker_pool {
struct ida worker_ida; /* L: for worker IDs */
struct workqueue_attrs *attrs; /* I: worker attributes */
struct hlist_node hash_node; /* R: unbound_pool_hash node */
int refcnt; /* refcnt for unbound pools */
/*
* The current concurrency level. As it's likely to be accessed
@ -156,6 +160,12 @@ struct worker_pool {
* cacheline.
*/
atomic_t nr_running ____cacheline_aligned_in_smp;
/*
* Destruction of pool is sched-RCU protected to allow dereferences
* from get_work_pool().
*/
struct rcu_head rcu;
} ____cacheline_aligned_in_smp;
/*
@ -218,6 +228,11 @@ struct workqueue_struct {
static struct kmem_cache *pwq_cache;
/* hash of all unbound pools keyed by pool->attrs */
static DEFINE_HASHTABLE(unbound_pool_hash, UNBOUND_POOL_HASH_ORDER);
static struct workqueue_attrs *unbound_std_wq_attrs[NR_STD_WORKER_POOLS];
struct workqueue_struct *system_wq __read_mostly;
EXPORT_SYMBOL_GPL(system_wq);
struct workqueue_struct *system_highpri_wq __read_mostly;
@ -1742,7 +1757,7 @@ static struct worker *create_worker(struct worker_pool *pool)
worker->pool = pool;
worker->id = id;
if (pool->cpu != WORK_CPU_UNBOUND)
if (pool->cpu >= 0)
worker->task = kthread_create_on_node(worker_thread,
worker, cpu_to_node(pool->cpu),
"kworker/%d:%d%s", pool->cpu, id, pri);
@ -3161,16 +3176,68 @@ fail:
return NULL;
}
static void copy_workqueue_attrs(struct workqueue_attrs *to,
const struct workqueue_attrs *from)
{
to->nice = from->nice;
cpumask_copy(to->cpumask, from->cpumask);
}
/*
* Hacky implementation of jhash of bitmaps which only considers the
* specified number of bits. We probably want a proper implementation in
* include/linux/jhash.h.
*/
static u32 jhash_bitmap(const unsigned long *bitmap, int bits, u32 hash)
{
int nr_longs = bits / BITS_PER_LONG;
int nr_leftover = bits % BITS_PER_LONG;
unsigned long leftover = 0;
if (nr_longs)
hash = jhash(bitmap, nr_longs * sizeof(long), hash);
if (nr_leftover) {
bitmap_copy(&leftover, bitmap + nr_longs, nr_leftover);
hash = jhash(&leftover, sizeof(long), hash);
}
return hash;
}
/* hash value of the content of @attr */
static u32 wqattrs_hash(const struct workqueue_attrs *attrs)
{
u32 hash = 0;
hash = jhash_1word(attrs->nice, hash);
hash = jhash_bitmap(cpumask_bits(attrs->cpumask), nr_cpu_ids, hash);
return hash;
}
/* content equality test */
static bool wqattrs_equal(const struct workqueue_attrs *a,
const struct workqueue_attrs *b)
{
if (a->nice != b->nice)
return false;
if (!cpumask_equal(a->cpumask, b->cpumask))
return false;
return true;
}
/**
* init_worker_pool - initialize a newly zalloc'd worker_pool
* @pool: worker_pool to initialize
*
* Initiailize a newly zalloc'd @pool. It also allocates @pool->attrs.
* Returns 0 on success, -errno on failure.
* Returns 0 on success, -errno on failure. Even on failure, all fields
* inside @pool proper are initialized and put_unbound_pool() can be called
* on @pool safely to release it.
*/
static int init_worker_pool(struct worker_pool *pool)
{
spin_lock_init(&pool->lock);
pool->id = -1;
pool->cpu = -1;
pool->flags |= POOL_DISASSOCIATED;
INIT_LIST_HEAD(&pool->worklist);
INIT_LIST_HEAD(&pool->idle_list);
@ -3187,12 +3254,136 @@ static int init_worker_pool(struct worker_pool *pool)
mutex_init(&pool->assoc_mutex);
ida_init(&pool->worker_ida);
INIT_HLIST_NODE(&pool->hash_node);
pool->refcnt = 1;
/* shouldn't fail above this point */
pool->attrs = alloc_workqueue_attrs(GFP_KERNEL);
if (!pool->attrs)
return -ENOMEM;
return 0;
}
static void rcu_free_pool(struct rcu_head *rcu)
{
struct worker_pool *pool = container_of(rcu, struct worker_pool, rcu);
ida_destroy(&pool->worker_ida);
free_workqueue_attrs(pool->attrs);
kfree(pool);
}
/**
* put_unbound_pool - put a worker_pool
* @pool: worker_pool to put
*
* Put @pool. If its refcnt reaches zero, it gets destroyed in sched-RCU
* safe manner.
*/
static void put_unbound_pool(struct worker_pool *pool)
{
struct worker *worker;
spin_lock_irq(&workqueue_lock);
if (--pool->refcnt) {
spin_unlock_irq(&workqueue_lock);
return;
}
/* sanity checks */
if (WARN_ON(!(pool->flags & POOL_DISASSOCIATED)) ||
WARN_ON(!list_empty(&pool->worklist))) {
spin_unlock_irq(&workqueue_lock);
return;
}
/* release id and unhash */
if (pool->id >= 0)
idr_remove(&worker_pool_idr, pool->id);
hash_del(&pool->hash_node);
spin_unlock_irq(&workqueue_lock);
/* lock out manager and destroy all workers */
mutex_lock(&pool->manager_arb);
spin_lock_irq(&pool->lock);
while ((worker = first_worker(pool)))
destroy_worker(worker);
WARN_ON(pool->nr_workers || pool->nr_idle);
spin_unlock_irq(&pool->lock);
mutex_unlock(&pool->manager_arb);
/* shut down the timers */
del_timer_sync(&pool->idle_timer);
del_timer_sync(&pool->mayday_timer);
/* sched-RCU protected to allow dereferences from get_work_pool() */
call_rcu_sched(&pool->rcu, rcu_free_pool);
}
/**
* get_unbound_pool - get a worker_pool with the specified attributes
* @attrs: the attributes of the worker_pool to get
*
* Obtain a worker_pool which has the same attributes as @attrs, bump the
* reference count and return it. If there already is a matching
* worker_pool, it will be used; otherwise, this function attempts to
* create a new one. On failure, returns NULL.
*/
static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs)
{
static DEFINE_MUTEX(create_mutex);
u32 hash = wqattrs_hash(attrs);
struct worker_pool *pool;
struct worker *worker;
mutex_lock(&create_mutex);
/* do we already have a matching pool? */
spin_lock_irq(&workqueue_lock);
hash_for_each_possible(unbound_pool_hash, pool, hash_node, hash) {
if (wqattrs_equal(pool->attrs, attrs)) {
pool->refcnt++;
goto out_unlock;
}
}
spin_unlock_irq(&workqueue_lock);
/* nope, create a new one */
pool = kzalloc(sizeof(*pool), GFP_KERNEL);
if (!pool || init_worker_pool(pool) < 0)
goto fail;
copy_workqueue_attrs(pool->attrs, attrs);
if (worker_pool_assign_id(pool) < 0)
goto fail;
/* create and start the initial worker */
worker = create_worker(pool);
if (!worker)
goto fail;
spin_lock_irq(&pool->lock);
start_worker(worker);
spin_unlock_irq(&pool->lock);
/* install */
spin_lock_irq(&workqueue_lock);
hash_add(unbound_pool_hash, &pool->hash_node, hash);
out_unlock:
spin_unlock_irq(&workqueue_lock);
mutex_unlock(&create_mutex);
return pool;
fail:
mutex_unlock(&create_mutex);
if (pool)
put_unbound_pool(pool);
return NULL;
}
static int alloc_and_link_pwqs(struct workqueue_struct *wq)
{
bool highpri = wq->flags & WQ_HIGHPRI;
@ -3217,7 +3408,12 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq)
if (!pwq)
return -ENOMEM;
pwq->pool = get_std_worker_pool(WORK_CPU_UNBOUND, highpri);
pwq->pool = get_unbound_pool(unbound_std_wq_attrs[highpri]);
if (!pwq->pool) {
kmem_cache_free(pwq_cache, pwq);
return -ENOMEM;
}
list_add_tail_rcu(&pwq->pwqs_node, &wq->pwqs);
}
@ -3395,6 +3591,15 @@ void destroy_workqueue(struct workqueue_struct *wq)
kfree(wq->rescuer);
}
/*
* We're the sole accessor of @wq at this point. Directly access
* the first pwq and put its pool.
*/
if (wq->flags & WQ_UNBOUND) {
pwq = list_first_entry(&wq->pwqs, struct pool_workqueue,
pwqs_node);
put_unbound_pool(pwq->pool);
}
free_pwqs(wq);
kfree(wq);
}
@ -3857,19 +4062,14 @@ static int __init init_workqueues(void)
hotcpu_notifier(workqueue_cpu_down_callback, CPU_PRI_WORKQUEUE_DOWN);
/* initialize CPU pools */
for_each_wq_cpu(cpu) {
for_each_possible_cpu(cpu) {
struct worker_pool *pool;
i = 0;
for_each_std_worker_pool(pool, cpu) {
BUG_ON(init_worker_pool(pool));
pool->cpu = cpu;
if (cpu != WORK_CPU_UNBOUND)
cpumask_copy(pool->attrs->cpumask, cpumask_of(cpu));
else
cpumask_setall(pool->attrs->cpumask);
cpumask_copy(pool->attrs->cpumask, cpumask_of(cpu));
pool->attrs->nice = std_nice[i++];
/* alloc pool ID */
@ -3878,14 +4078,13 @@ static int __init init_workqueues(void)
}
/* create the initial worker */
for_each_online_wq_cpu(cpu) {
for_each_online_cpu(cpu) {
struct worker_pool *pool;
for_each_std_worker_pool(pool, cpu) {
struct worker *worker;
if (cpu != WORK_CPU_UNBOUND)
pool->flags &= ~POOL_DISASSOCIATED;
pool->flags &= ~POOL_DISASSOCIATED;
worker = create_worker(pool);
BUG_ON(!worker);
@ -3895,6 +4094,18 @@ static int __init init_workqueues(void)
}
}
/* create default unbound wq attrs */
for (i = 0; i < NR_STD_WORKER_POOLS; i++) {
struct workqueue_attrs *attrs;
BUG_ON(!(attrs = alloc_workqueue_attrs(GFP_KERNEL)));
attrs->nice = std_nice[i];
cpumask_setall(attrs->cpumask);
unbound_std_wq_attrs[i] = attrs;
}
system_wq = alloc_workqueue("events", 0, 0);
system_highpri_wq = alloc_workqueue("events_highpri", WQ_HIGHPRI, 0);
system_long_wq = alloc_workqueue("events_long", 0, 0);