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Commit 52722794 authored by Tejun Heo's avatar Tejun Heo
Browse files

async: keep pending tasks on async_domain and remove async_pending 



Async kept single global pending list and per-domain running lists.
When an async item is queued, it's put on the global pending list.
The item is moved to the per-domain running list when its execution
starts.

At this point, this design complicates execution and synchronization
without bringing any benefit.  The list only matters for
synchronization which doesn't care whether a given async item is
pending or executing.  Also, global synchronization is done by
iterating through all active registered async_domains, so the global
async_pending list doesn't help anything either.

Rename async_domain->running to async_domain->pending and put async
items directly there and remove when execution completes.  This
simplifies lowest_in_progress() a lot - the first item on the pending
list is the one with the lowest cookie, and async_run_entry_fn()
doesn't have to mess with moving the item from pending to running.

After the change, whether a domain is empty or not can be trivially
determined by looking at async_domain->pending.  Remove
async_domain->count and use list_empty() on pending instead.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Dan Williams <djbw@fb.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
parent c68eee14

include/linux/async.h

+3 −6
Original line number Diff line number Diff line
@@ -19,8 +19,7 @@ typedef u64 async_cookie_t; 
typedef void (async_func_ptr) (void *data, async_cookie_t cookie);

struct async_domain {

	struct list_head node;

	struct list_head running;

	int count;

	struct list_head pending;

	unsigned registered:1;

};
@@ -29,8 +28,7 @@ struct async_domain { 
 */

#define ASYNC_DOMAIN(_name) \

	struct async_domain _name = { .node = LIST_HEAD_INIT(_name.node), \

				      .running = LIST_HEAD_INIT(_name.running), \

				      .count = 0, \

				      .pending = LIST_HEAD_INIT(_name.pending), \

				      .registered = 1 }



/*
@@ -39,8 +37,7 @@ struct async_domain { 
 */

#define ASYNC_DOMAIN_EXCLUSIVE(_name) \

	struct async_domain _name = { .node = LIST_HEAD_INIT(_name.node), \

				      .running = LIST_HEAD_INIT(_name.running), \

				      .count = 0, \

				      .pending = LIST_HEAD_INIT(_name.pending), \

				      .registered = 0 }



extern async_cookie_t async_schedule(async_func_ptr *ptr, void *data);

kernel/async.c

+14 −49
Original line number Diff line number Diff line
@@ -64,7 +64,6 @@ static async_cookie_t next_cookie = 1; 
#define MAX_WORK		32768

#define ASYNC_COOKIE_MAX	ULLONG_MAX	/* infinity cookie */



static LIST_HEAD(async_pending);

static ASYNC_DOMAIN(async_dfl_domain);

static LIST_HEAD(async_domains);

static DEFINE_SPINLOCK(async_lock);
@@ -83,42 +82,17 @@ static DECLARE_WAIT_QUEUE_HEAD(async_done); 


static atomic_t entry_count;





/*

 * MUST be called with the lock held!

 */

static async_cookie_t __lowest_in_progress(struct async_domain *domain)

{

	async_cookie_t first_running = ASYNC_COOKIE_MAX;

	async_cookie_t first_pending = ASYNC_COOKIE_MAX;

	struct async_entry *entry;



	/*

	 * Both running and pending lists are sorted but not disjoint.

	 * Take the first cookies from both and return the min.

	 */

	if (!list_empty(&domain->running)) {

		entry = list_first_entry(&domain->running, typeof(*entry), list);

		first_running = entry->cookie;

	}



	list_for_each_entry(entry, &async_pending, list) {

		if (entry->domain == domain) {

			first_pending = entry->cookie;

			break;

		}

	}



	return min(first_running, first_pending);

}



static async_cookie_t lowest_in_progress(struct async_domain *domain)

{

	async_cookie_t ret = ASYNC_COOKIE_MAX;

	unsigned long flags;

	async_cookie_t ret;



	spin_lock_irqsave(&async_lock, flags);

	ret = __lowest_in_progress(domain);

	if (!list_empty(&domain->pending)) {

		struct async_entry *first = list_first_entry(&domain->pending,

						struct async_entry, list);

		ret = first->cookie;

	}

	spin_unlock_irqrestore(&async_lock, flags);

	return ret;

}
@@ -130,20 +104,11 @@ static void async_run_entry_fn(struct work_struct *work) 
{

	struct async_entry *entry =

		container_of(work, struct async_entry, work);

	struct async_entry *pos;

	unsigned long flags;

	ktime_t uninitialized_var(calltime), delta, rettime;

	struct async_domain *domain = entry->domain;



	/* 1) move self to the running queue, make sure it stays sorted */

	spin_lock_irqsave(&async_lock, flags);

	list_for_each_entry_reverse(pos, &domain->running, list)

		if (entry->cookie < pos->cookie)

			break;

	list_move_tail(&entry->list, &pos->list);

	spin_unlock_irqrestore(&async_lock, flags);



	/* 2) run (and print duration) */

	/* 1) run (and print duration) */

	if (initcall_debug && system_state == SYSTEM_BOOTING) {

		printk(KERN_DEBUG "calling  %lli_%pF @ %i\n",

			(long long)entry->cookie,
@@ -160,19 +125,19 @@ static void async_run_entry_fn(struct work_struct *work) 
			(long long)ktime_to_ns(delta) >> 10);

	}



	/* 3) remove self from the running queue */

	/* 2) remove self from the pending queues */

	spin_lock_irqsave(&async_lock, flags);

	list_del(&entry->list);

	if (domain->registered && --domain->count == 0)

	if (domain->registered && list_empty(&domain->pending))

		list_del_init(&domain->node);



	/* 4) free the entry */

	/* 3) free the entry */

	kfree(entry);

	atomic_dec(&entry_count);



	spin_unlock_irqrestore(&async_lock, flags);



	/* 5) wake up any waiters */

	/* 4) wake up any waiters */

	wake_up(&async_done);

}
@@ -206,9 +171,9 @@ static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct a 


	spin_lock_irqsave(&async_lock, flags);

	newcookie = entry->cookie = next_cookie++;

	list_add_tail(&entry->list, &async_pending);

	if (domain->registered && domain->count++ == 0)

	if (domain->registered && list_empty(&domain->pending))

		list_add_tail(&domain->node, &async_domains);

	list_add_tail(&entry->list, &domain->pending);

	atomic_inc(&entry_count);

	spin_unlock_irqrestore(&async_lock, flags);
@@ -290,7 +255,7 @@ void async_unregister_domain(struct async_domain *domain) 
	mutex_lock(&async_register_mutex);

	spin_lock_irq(&async_lock);

	WARN_ON(!domain->registered || !list_empty(&domain->node) ||

		!list_empty(&domain->running));

		!list_empty(&domain->pending));

	domain->registered = 0;

	spin_unlock_irq(&async_lock);

	mutex_unlock(&async_register_mutex);