[PATCH 03/17] workqueue: make GCWQ_DISASSOCIATED a pool flag

Tejun Heo
2013-01-17T01:46:49Z

Make GCWQ_DISASSOCIATED a pool flag POOL_DISASSOCIATED. This patch
doesn't change locking - DISASSOCIATED on both pools of a CPU are set
or clear together while holding gcwq->lock. It shouldn't cause any
functional difference.

This is part of an effort to remove global_cwq and make worker_pool
the top level abstraction, which in turn will help implementing worker
pools with user-specified attributes.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
kernel/workqueue.c | 66 +++++++++++++++++++++++++++++-------------------------
1 file changed, 35 insertions(+), 31 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 5e74cd2..8feef7e 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -48,26 +48,28 @@
enum {
/*
* global_cwq flags
+ */
+ GCWQ_FREEZING = 1 << 1, /* freeze in progress */
+
+ /*
+ * worker_pool flags
*
- * A bound gcwq is either associated or disassociated with its CPU.
+ * A bound pool is either associated or disassociated with its CPU.
* While associated (!DISASSOCIATED), all workers are bound to the
* CPU and none has %WORKER_UNBOUND set and concurrency management
* is in effect.
*
* While DISASSOCIATED, the cpu may be offline and all workers have
* %WORKER_UNBOUND set and concurrency management disabled, and may
- * be executing on any CPU. The gcwq behaves as an unbound one.
+ * be executing on any CPU. The pool behaves as an unbound one.
*
* Note that DISASSOCIATED can be flipped only while holding
- * assoc_mutex of all pools on the gcwq to avoid changing binding
- * state while create_worker() is in progress.
+ * assoc_mutex to avoid changing binding state while
+ * create_worker() is in progress.
*/
- GCWQ_DISASSOCIATED = 1 << 0, /* cpu can't serve workers */
- GCWQ_FREEZING = 1 << 1, /* freeze in progress */
-
- /* pool flags */
POOL_MANAGE_WORKERS = 1 << 0, /* need to manage workers */
POOL_MANAGING_WORKERS = 1 << 1, /* managing workers */
+ POOL_DISASSOCIATED = 1 << 2, /* cpu can't serve workers */

/* worker flags */
WORKER_STARTED = 1 << 0, /* started */
@@ -115,7 +117,7 @@ enum {
* X: During normal operation, modification requires gcwq->lock and
* should be done only from local cpu. Either disabling preemption
* on local cpu or grabbing gcwq->lock is enough for read access.
- * If GCWQ_DISASSOCIATED is set, it's identical to L.
+ * If POOL_DISASSOCIATED is set, it's identical to L.
*
* F: wq->flush_mutex protected.
*
@@ -165,7 +167,7 @@ struct worker_pool {
struct timer_list idle_timer; /* L: worker idle timeout */
struct timer_list mayday_timer; /* L: SOS timer for workers */

- struct mutex assoc_mutex; /* protect GCWQ_DISASSOCIATED */
+ struct mutex assoc_mutex; /* protect POOL_DISASSOCIATED */
struct ida worker_ida; /* L: for worker IDs */
};

@@ -466,9 +468,9 @@ static DEFINE_PER_CPU(struct global_cwq, global_cwq);
static DEFINE_PER_CPU_SHARED_ALIGNED(atomic_t, pool_nr_running[NR_STD_WORKER_POOLS]);

/*
- * Global cpu workqueue and nr_running counter for unbound gcwq. The
- * gcwq is always online, has GCWQ_DISASSOCIATED set, and all its
- * workers have WORKER_UNBOUND set.
+ * Global cpu workqueue and nr_running counter for unbound gcwq. The pools
+ * for online CPUs have POOL_DISASSOCIATED set, and all their workers have
+ * WORKER_UNBOUND set.
*/
static struct global_cwq unbound_global_cwq;
static atomic_t unbound_pool_nr_running[NR_STD_WORKER_POOLS] = {
@@ -1493,7 +1495,6 @@ EXPORT_SYMBOL_GPL(mod_delayed_work);
static void worker_enter_idle(struct worker *worker)
{
struct worker_pool *pool = worker->pool;
- struct global_cwq *gcwq = pool->gcwq;

BUG_ON(worker->flags & WORKER_IDLE);
BUG_ON(!list_empty(&worker->entry) &&
@@ -1516,7 +1517,7 @@ static void worker_enter_idle(struct worker *worker)
* nr_running, the warning may trigger spuriously. Check iff
* unbind is not in progress.
*/
- WARN_ON_ONCE(!(gcwq->flags & GCWQ_DISASSOCIATED) &&
+ WARN_ON_ONCE(!(pool->flags & POOL_DISASSOCIATED) &&
pool->nr_workers == pool->nr_idle &&
atomic_read(get_pool_nr_running(pool)));
}
@@ -1557,7 +1558,7 @@ static void worker_leave_idle(struct worker *worker)
* [dis]associated in the meantime.
*
* This function tries set_cpus_allowed() and locks gcwq and verifies the
- * binding against %GCWQ_DISASSOCIATED which is set during
+ * binding against %POOL_DISASSOCIATED which is set during
* %CPU_DOWN_PREPARE and cleared during %CPU_ONLINE, so if the worker
* enters idle state or fetches works without dropping lock, it can
* guarantee the scheduling requirement described in the first paragraph.
@@ -1573,7 +1574,8 @@ static void worker_leave_idle(struct worker *worker)
static bool worker_maybe_bind_and_lock(struct worker *worker)
__acquires(&gcwq->lock)
{
- struct global_cwq *gcwq = worker->pool->gcwq;
+ struct worker_pool *pool = worker->pool;
+ struct global_cwq *gcwq = pool->gcwq;
struct task_struct *task = worker->task;

while (true) {
@@ -1581,13 +1583,13 @@ __acquires(&gcwq->lock)
* The following call may fail, succeed or succeed
* without actually migrating the task to the cpu if
* it races with cpu hotunplug operation. Verify
- * against GCWQ_DISASSOCIATED.
+ * against POOL_DISASSOCIATED.
*/
- if (!(gcwq->flags & GCWQ_DISASSOCIATED))
+ if (!(pool->flags & POOL_DISASSOCIATED))
set_cpus_allowed_ptr(task, get_cpu_mask(gcwq->cpu));

spin_lock_irq(&gcwq->lock);
- if (gcwq->flags & GCWQ_DISASSOCIATED)
+ if (pool->flags & POOL_DISASSOCIATED)
return false;
if (task_cpu(task) == gcwq->cpu &&
cpumask_equal(&current->cpus_allowed,
@@ -1785,14 +1787,14 @@ static struct worker *create_worker(struct worker_pool *pool)

/*
* Determine CPU binding of the new worker depending on
- * %GCWQ_DISASSOCIATED. The caller is responsible for ensuring the
+ * %POOL_DISASSOCIATED. The caller is responsible for ensuring the
* flag remains stable across this function. See the comments
* above the flag definition for details.
*
* As an unbound worker may later become a regular one if CPU comes
* online, make sure every worker has %PF_THREAD_BOUND set.
*/
- if (!(gcwq->flags & GCWQ_DISASSOCIATED)) {
+ if (!(pool->flags & POOL_DISASSOCIATED)) {
kthread_bind(worker->task, gcwq->cpu);
} else {
worker->task->flags |= PF_THREAD_BOUND;
@@ -2153,10 +2155,10 @@ __acquires(&gcwq->lock)
/*
* Ensure we're on the correct CPU. DISASSOCIATED test is
* necessary to avoid spurious warnings from rescuers servicing the
- * unbound or a disassociated gcwq.
+ * unbound or a disassociated pool.
*/
WARN_ON_ONCE(!(worker->flags & WORKER_UNBOUND) &&
- !(gcwq->flags & GCWQ_DISASSOCIATED) &&
+ !(pool->flags & POOL_DISASSOCIATED) &&
raw_smp_processor_id() != gcwq->cpu);

/*
@@ -3481,7 +3483,7 @@ EXPORT_SYMBOL_GPL(work_busy);
* gcwqs serve mix of short, long and very long running works making
* blocked draining impractical.
*
- * This is solved by allowing a gcwq to be disassociated from the CPU
+ * This is solved by allowing the pools to be disassociated from the CPU
* running as an unbound one and allowing it to be reattached later if the
* cpu comes back online.
*/
@@ -3531,7 +3533,8 @@ static void gcwq_unbind_fn(struct work_struct *work)
for_each_busy_worker(worker, i, pos, gcwq)
worker->flags |= WORKER_UNBOUND;

- gcwq->flags |= GCWQ_DISASSOCIATED;
+ for_each_worker_pool(pool, gcwq)
+ pool->flags |= POOL_DISASSOCIATED;

gcwq_release_assoc_and_unlock(gcwq);

@@ -3590,7 +3593,8 @@ static int __cpuinit workqueue_cpu_up_callback(struct notifier_block *nfb,
case CPU_DOWN_FAILED:
case CPU_ONLINE:
gcwq_claim_assoc_and_lock(gcwq);
- gcwq->flags &= ~GCWQ_DISASSOCIATED;
+ for_each_worker_pool(pool, gcwq)
+ pool->flags &= ~POOL_DISASSOCIATED;
rebind_workers(gcwq);
gcwq_release_assoc_and_unlock(gcwq);
break;
@@ -3815,12 +3819,12 @@ static int __init init_workqueues(void)

spin_lock_init(&gcwq->lock);
gcwq->cpu = cpu;
- gcwq->flags |= GCWQ_DISASSOCIATED;

hash_init(gcwq->busy_hash);

for_each_worker_pool(pool, gcwq) {
pool->gcwq = gcwq;
+ pool->flags |= POOL_DISASSOCIATED;
INIT_LIST_HEAD(&pool->worklist);
INIT_LIST_HEAD(&pool->idle_list);

@@ -3841,12 +3845,12 @@ static int __init init_workqueues(void)
struct global_cwq *gcwq = get_gcwq(cpu);
struct worker_pool *pool;

- if (cpu != WORK_CPU_UNBOUND)
- gcwq->flags &= ~GCWQ_DISASSOCIATED;
-
for_each_worker_pool(pool, gcwq) {
struct worker *worker;

+ if (cpu != WORK_CPU_UNBOUND)
+ pool->flags &= ~POOL_DISASSOCIATED;
+
worker = create_worker(pool);
BUG_ON(!worker);
spin_lock_irq(&gcwq->lock);
--
1.8.0.2