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workqueue: move nr_running into worker_pool

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As nr_running is likely to be accessed from other CPUs during
try_to_wake_up(), it was kept outside worker_pool; however, while less
frequent, other fields in worker_pool are accessed from other CPUs
for, e.g., non-reentrancy check.  Also, with recent pool related
changes, accessing nr_running matching the worker_pool isn't as simple
as it used to be.

Move nr_running inside worker_pool.  Keep it aligned to cacheline and
define CPU pools using DEFINE_PER_CPU_SHARED_ALIGNED().  This should
give at least the same cacheline behavior.

get_pool_nr_running() is replaced with direct pool->nr_running
accesses.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Joonsoo Kim <js1304@gmail.com>
This commit is contained in:
Tejun Heo 2013-01-24 11:39:44 -08:00
parent 1606283622
commit e19e397a85
1 changed files with 22 additions and 41 deletions
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63
kernel/workqueue.c
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@ -144,6 +144,13 @@ struct worker_pool {
struct mutex assoc_mutex; /* protect POOL_DISASSOCIATED */
struct ida worker_ida; /* L: for worker IDs */
/*
* The current concurrency level. As it's likely to be accessed
* from other CPUs during try_to_wake_up(), put it in a separate
* cacheline.
*/
atomic_t nr_running ____cacheline_aligned_in_smp;
} ____cacheline_aligned_in_smp;
/*
@ -417,23 +424,12 @@ static LIST_HEAD(workqueues);
static bool workqueue_freezing; /* W: have wqs started freezing? */
/*
* The CPU standard worker pools. nr_running is the only field which is
* expected to be used frequently by other cpus via try_to_wake_up(). Put
* it in a separate cacheline.
*/
static DEFINE_PER_CPU(struct worker_pool [NR_STD_WORKER_POOLS],
cpu_std_worker_pools);
static DEFINE_PER_CPU_SHARED_ALIGNED(atomic_t [NR_STD_WORKER_POOLS],
cpu_std_pool_nr_running);
/*
* Standard worker pools and nr_running counter for unbound CPU. The pools
* have POOL_DISASSOCIATED set, and all workers have WORKER_UNBOUND set.
* The CPU and unbound standard worker pools. The unbound ones have
* POOL_DISASSOCIATED set, and their workers have WORKER_UNBOUND set.
*/
static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS],
cpu_std_worker_pools);
static struct worker_pool unbound_std_worker_pools[NR_STD_WORKER_POOLS];
static atomic_t unbound_std_pool_nr_running[NR_STD_WORKER_POOLS] = {
[0 ... NR_STD_WORKER_POOLS - 1] = ATOMIC_INIT(0), /* always 0 */
};
/* idr of all pools */
static DEFINE_MUTEX(worker_pool_idr_mutex);
@ -483,17 +479,6 @@ static struct worker_pool *get_std_worker_pool(int cpu, bool highpri)
return &pools[highpri];
}
static atomic_t *get_pool_nr_running(struct worker_pool *pool)
{
int cpu = pool->cpu;
int idx = std_worker_pool_pri(pool);
if (cpu != WORK_CPU_UNBOUND)
return &per_cpu(cpu_std_pool_nr_running, cpu)[idx];
else
return &unbound_std_pool_nr_running[idx];
}
static struct cpu_workqueue_struct *get_cwq(unsigned int cpu,
struct workqueue_struct *wq)
{
@ -654,7 +639,7 @@ static bool work_is_canceling(struct work_struct *work)
static bool __need_more_worker(struct worker_pool *pool)
{
return !atomic_read(get_pool_nr_running(pool));
return !atomic_read(&pool->nr_running);
}
/*
@ -679,9 +664,8 @@ static bool may_start_working(struct worker_pool *pool)
/* Do I need to keep working? Called from currently running workers. */
static bool keep_working(struct worker_pool *pool)
{
atomic_t *nr_running = get_pool_nr_running(pool);
return !list_empty(&pool->worklist) && atomic_read(nr_running) <= 1;
return !list_empty(&pool->worklist) &&
atomic_read(&pool->nr_running) <= 1;
}
/* Do we need a new worker? Called from manager. */
@ -761,7 +745,7 @@ void wq_worker_waking_up(struct task_struct *task, unsigned int cpu)
if (!(worker->flags & WORKER_NOT_RUNNING)) {
WARN_ON_ONCE(worker->pool->cpu != cpu);
atomic_inc(get_pool_nr_running(worker->pool));
atomic_inc(&worker->pool->nr_running);
}
}
@ -785,7 +769,6 @@ struct task_struct *wq_worker_sleeping(struct task_struct *task,
{
struct worker *worker = kthread_data(task), *to_wakeup = NULL;
struct worker_pool *pool;
atomic_t *nr_running;
/*
* Rescuers, which may not have all the fields set up like normal
@ -796,7 +779,6 @@ struct task_struct *wq_worker_sleeping(struct task_struct *task,
return NULL;
pool = worker->pool;
nr_running = get_pool_nr_running(pool);
/* this can only happen on the local cpu */
BUG_ON(cpu != raw_smp_processor_id());
@ -812,7 +794,8 @@ struct task_struct *wq_worker_sleeping(struct task_struct *task,
* manipulating idle_list, so dereferencing idle_list without pool
* lock is safe.
*/
if (atomic_dec_and_test(nr_running) && !list_empty(&pool->worklist))
if (atomic_dec_and_test(&pool->nr_running) &&
!list_empty(&pool->worklist))
to_wakeup = first_worker(pool);
return to_wakeup ? to_wakeup->task : NULL;
}
@ -844,14 +827,12 @@ static inline void worker_set_flags(struct worker *worker, unsigned int flags,
*/
if ((flags & WORKER_NOT_RUNNING) &&
!(worker->flags & WORKER_NOT_RUNNING)) {
atomic_t *nr_running = get_pool_nr_running(pool);
if (wakeup) {
if (atomic_dec_and_test(nr_running) &&
if (atomic_dec_and_test(&pool->nr_running) &&
!list_empty(&pool->worklist))
wake_up_worker(pool);
} else
atomic_dec(nr_running);
atomic_dec(&pool->nr_running);
}
worker->flags |= flags;
@ -883,7 +864,7 @@ static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
*/
if ((flags & WORKER_NOT_RUNNING) && (oflags & WORKER_NOT_RUNNING))
if (!(worker->flags & WORKER_NOT_RUNNING))
atomic_inc(get_pool_nr_running(pool));
atomic_inc(&pool->nr_running);
}
/**
@ -1518,7 +1499,7 @@ static void worker_enter_idle(struct worker *worker)
*/
WARN_ON_ONCE(!(pool->flags & POOL_DISASSOCIATED) &&
pool->nr_workers == pool->nr_idle &&
atomic_read(get_pool_nr_running(pool)));
atomic_read(&pool->nr_running));
}
/**
@ -3506,7 +3487,7 @@ static void wq_unbind_fn(struct work_struct *work)
* didn't already.
*/
for_each_std_worker_pool(pool, cpu)
atomic_set(get_pool_nr_running(pool), 0);
atomic_set(&pool->nr_running, 0);
}
/*