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Commit e19e397a authored by Tejun Heo's avatar Tejun Heo
Browse files

workqueue: move nr_running into worker_pool 



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: default avatarTejun Heo <tj@kernel.org>
Cc: Joonsoo Kim <js1304@gmail.com>
parent 16062836

kernel/workqueue.c

+22 −41
Original line number Diff line number Diff line
@@ -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.

 * 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(struct worker_pool [NR_STD_WORKER_POOLS],

static DEFINE_PER_CPU_SHARED_ALIGNED(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.

 */

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);

}



/*