Commit e2d74ac0 authored by Jens Axboe's avatar Jens Axboe
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[PATCH] [BLOCK] cfq-iosched: change cfq io context linking from list to tree 



On setups with many disks, we spend a considerable amount of time
looking up the process-disk mapping on each queue of io. Testing with
a NULL based block driver, this costs 40-50% reduction in throughput
for 1000 disks.

Signed-off-by: default avatarJens Axboe <axboe@suse.de>
parent 329b10bb

block/cfq-iosched.c

+95 −110
Original line number Diff line number Diff line
@@ -1190,19 +1190,19 @@ cfq_find_cfq_hash(struct cfq_data *cfqd, unsigned int key, unsigned short prio) 
	return __cfq_find_cfq_hash(cfqd, key, prio, hash_long(key, CFQ_QHASH_SHIFT));

}



static void cfq_free_io_context(struct cfq_io_context *cic)

static void cfq_free_io_context(struct io_context *ioc)

{

	struct cfq_io_context *__cic;

	struct list_head *entry, *next;

	int freed = 1;

	struct rb_node *n;

	int freed = 0;



	list_for_each_safe(entry, next, &cic->list) {

		__cic = list_entry(entry, struct cfq_io_context, list);

	while ((n = rb_first(&ioc->cic_root)) != NULL) {

		__cic = rb_entry(n, struct cfq_io_context, rb_node);

		rb_erase(&__cic->rb_node, &ioc->cic_root);

		kmem_cache_free(cfq_ioc_pool, __cic);

		freed++;

	}



	kmem_cache_free(cfq_ioc_pool, cic);

	if (atomic_sub_and_test(freed, &ioc_count) && ioc_gone)

		complete(ioc_gone);

}
@@ -1210,8 +1210,7 @@ static void cfq_free_io_context(struct cfq_io_context *cic) 
static void cfq_trim(struct io_context *ioc)

{

	ioc->set_ioprio = NULL;

	if (ioc->cic)

		cfq_free_io_context(ioc->cic);

	cfq_free_io_context(ioc);

}



/*
@@ -1250,26 +1249,26 @@ static void cfq_exit_single_io_context(struct cfq_io_context *cic) 
	spin_unlock(q->queue_lock);

}



static void cfq_exit_io_context(struct cfq_io_context *cic)

static void cfq_exit_io_context(struct io_context *ioc)

{

	struct cfq_io_context *__cic;

	struct list_head *entry;

	unsigned long flags;



	local_irq_save(flags);

	struct rb_node *n;



	/*

	 * put the reference this task is holding to the various queues

	 */

	read_lock(&cfq_exit_lock);

	list_for_each(entry, &cic->list) {

		__cic = list_entry(entry, struct cfq_io_context, list);

	read_lock_irqsave(&cfq_exit_lock, flags);



	n = rb_first(&ioc->cic_root);

	while (n != NULL) {

		__cic = rb_entry(n, struct cfq_io_context, rb_node);



		cfq_exit_single_io_context(__cic);

		n = rb_next(n);

	}



	cfq_exit_single_io_context(cic);

	read_unlock(&cfq_exit_lock);

	local_irq_restore(flags);

	read_unlock_irqrestore(&cfq_exit_lock, flags);

}



static struct cfq_io_context *
@@ -1278,10 +1277,10 @@ cfq_alloc_io_context(struct cfq_data *cfqd, gfp_t gfp_mask) 
	struct cfq_io_context *cic = kmem_cache_alloc(cfq_ioc_pool, gfp_mask);



	if (cic) {

		INIT_LIST_HEAD(&cic->list);

		RB_CLEAR(&cic->rb_node);

		cic->key = NULL;

		cic->cfqq[ASYNC] = NULL;

		cic->cfqq[SYNC] = NULL;

		cic->key = NULL;

		cic->last_end_request = jiffies;

		cic->ttime_total = 0;

		cic->ttime_samples = 0;
@@ -1373,15 +1372,17 @@ static inline void changed_ioprio(struct cfq_io_context *cic) 
static int cfq_ioc_set_ioprio(struct io_context *ioc, unsigned int ioprio)

{

	struct cfq_io_context *cic;

	struct rb_node *n;



	write_lock(&cfq_exit_lock);



	cic = ioc->cic;



	changed_ioprio(cic);

	n = rb_first(&ioc->cic_root);

	while (n != NULL) {

		cic = rb_entry(n, struct cfq_io_context, rb_node);

 

	list_for_each_entry(cic, &cic->list, list)

		changed_ioprio(cic);

		n = rb_next(n);

	}



	write_unlock(&cfq_exit_lock);
@@ -1445,106 +1446,86 @@ cfq_get_queue(struct cfq_data *cfqd, unsigned int key, struct task_struct *tsk, 
	return cfqq;

}



/*

 * Setup general io context and cfq io context. There can be several cfq

 * io contexts per general io context, if this process is doing io to more

 * than one device managed by cfq. Note that caller is holding a reference to

 * cfqq, so we don't need to worry about it disappearing

 */

static struct cfq_io_context *

cfq_get_io_context(struct cfq_data *cfqd, pid_t pid, gfp_t gfp_mask)

cfq_cic_rb_lookup(struct cfq_data *cfqd, struct io_context *ioc)

{

	struct io_context *ioc = NULL;

	struct rb_node *n = ioc->cic_root.rb_node;

	struct cfq_io_context *cic;

	void *key = cfqd;



	might_sleep_if(gfp_mask & __GFP_WAIT);

	while (n) {

		cic = rb_entry(n, struct cfq_io_context, rb_node);



		if (key < cic->key)

			n = n->rb_left;

		else if (key > cic->key)

			n = n->rb_right;

		else

			return cic;

	}



	ioc = get_io_context(gfp_mask);

	if (!ioc)

	return NULL;

}



restart:

	if ((cic = ioc->cic) == NULL) {

		cic = cfq_alloc_io_context(cfqd, gfp_mask);

static inline void

cfq_cic_link(struct cfq_data *cfqd, struct io_context *ioc,

	     struct cfq_io_context *cic)

{

	struct rb_node **p = &ioc->cic_root.rb_node;

	struct rb_node *parent = NULL;

	struct cfq_io_context *__cic;



		if (cic == NULL)

			goto err;

	read_lock(&cfq_exit_lock);



		/*

		 * manually increment generic io_context usage count, it

		 * cannot go away since we are already holding one ref to it

		 */

	cic->ioc = ioc;

	cic->key = cfqd;

		read_lock(&cfq_exit_lock);



	ioc->set_ioprio = cfq_ioc_set_ioprio;

		ioc->cic = cic;

		list_add(&cic->queue_list, &cfqd->cic_list);

		read_unlock(&cfq_exit_lock);

	} else {

		struct cfq_io_context *__cic;



		/*

		 * the first cic on the list is actually the head itself

		 */

		if (cic->key == cfqd)

			goto out;

	while (*p) {

		parent = *p;

		__cic = rb_entry(parent, struct cfq_io_context, rb_node);



		if (unlikely(!cic->key)) {

			read_lock(&cfq_exit_lock);

			if (list_empty(&cic->list))

				ioc->cic = NULL;

		if (cic->key < __cic->key)

			p = &(*p)->rb_left;

		else if (cic->key > __cic->key)

			p = &(*p)->rb_right;

		else

				ioc->cic = list_entry(cic->list.next,

						      struct cfq_io_context,

						      list);

			read_unlock(&cfq_exit_lock);

			kmem_cache_free(cfq_ioc_pool, cic);

			atomic_dec(&ioc_count);

			goto restart;

			BUG();

	}



		/*

		 * cic exists, check if we already are there. linear search

		 * should be ok here, the list will usually not be more than

		 * 1 or a few entries long

		 */

		list_for_each_entry(__cic, &cic->list, list) {

			/*

			 * this process is already holding a reference to

			 * this queue, so no need to get one more

			 */

			if (__cic->key == cfqd) {

				cic = __cic;

				goto out;

			}

			if (unlikely(!__cic->key)) {

				read_lock(&cfq_exit_lock);

				list_del(&__cic->list);

	rb_link_node(&cic->rb_node, parent, p);

	rb_insert_color(&cic->rb_node, &ioc->cic_root);

	list_add(&cic->queue_list, &cfqd->cic_list);

	read_unlock(&cfq_exit_lock);

				kmem_cache_free(cfq_ioc_pool, __cic);

				atomic_dec(&ioc_count);

				goto restart;

			}

}



/*

		 * nope, process doesn't have a cic assoicated with this

		 * cfqq yet. get a new one and add to list

 * Setup general io context and cfq io context. There can be several cfq

 * io contexts per general io context, if this process is doing io to more

 * than one device managed by cfq.

 */

		__cic = cfq_alloc_io_context(cfqd, gfp_mask);

		if (__cic == NULL)

			goto err;

static struct cfq_io_context *

cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)

{

	struct io_context *ioc = NULL;

	struct cfq_io_context *cic;



		__cic->ioc = ioc;

		__cic->key = cfqd;

		read_lock(&cfq_exit_lock);

		list_add(&__cic->list, &cic->list);

		list_add(&__cic->queue_list, &cfqd->cic_list);

		read_unlock(&cfq_exit_lock);

		cic = __cic;

	}

	might_sleep_if(gfp_mask & __GFP_WAIT);



	ioc = get_io_context(gfp_mask);

	if (!ioc)

		return NULL;



	cic = cfq_cic_rb_lookup(cfqd, ioc);

	if (cic)

		goto out;



	cic = cfq_alloc_io_context(cfqd, gfp_mask);

	if (cic == NULL)

		goto err;



	cfq_cic_link(cfqd, ioc, cic);

out:

	return cic;

err:
@@ -1965,7 +1946,7 @@ cfq_set_request(request_queue_t *q, struct request *rq, struct bio *bio, 


	might_sleep_if(gfp_mask & __GFP_WAIT);



	cic = cfq_get_io_context(cfqd, key, gfp_mask);

	cic = cfq_get_io_context(cfqd, gfp_mask);



	spin_lock_irqsave(q->queue_lock, flags);
@@ -2133,10 +2114,13 @@ static void cfq_exit_queue(elevator_t *e) 
	request_queue_t *q = cfqd->queue;



	cfq_shutdown_timer_wq(cfqd);



	write_lock(&cfq_exit_lock);

	spin_lock_irq(q->queue_lock);



	if (cfqd->active_queue)

		__cfq_slice_expired(cfqd, cfqd->active_queue, 0);



	while (!list_empty(&cfqd->cic_list)) {

		struct cfq_io_context *cic = list_entry(cfqd->cic_list.next,

							struct cfq_io_context,
@@ -2152,6 +2136,7 @@ static void cfq_exit_queue(elevator_t *e) 
		cic->key = NULL;

		list_del_init(&cic->queue_list);

	}



	spin_unlock_irq(q->queue_lock);

	write_unlock(&cfq_exit_lock);

block/ll_rw_blk.c

+13 −6
Original line number Diff line number Diff line
@@ -3539,11 +3539,15 @@ void put_io_context(struct io_context *ioc) 
	BUG_ON(atomic_read(&ioc->refcount) == 0);



	if (atomic_dec_and_test(&ioc->refcount)) {

		struct cfq_io_context *cic;



		rcu_read_lock();

		if (ioc->aic && ioc->aic->dtor)

			ioc->aic->dtor(ioc->aic);

		if (ioc->cic && ioc->cic->dtor)

			ioc->cic->dtor(ioc->cic);

		if (ioc->cic_root.rb_node != NULL) {

			cic = rb_entry(rb_first(&ioc->cic_root), struct cfq_io_context, rb_node);

			cic->dtor(ioc);

		}

		rcu_read_unlock();



		kmem_cache_free(iocontext_cachep, ioc);
@@ -3556,6 +3560,7 @@ void exit_io_context(void) 
{

	unsigned long flags;

	struct io_context *ioc;

	struct cfq_io_context *cic;



	local_irq_save(flags);

	task_lock(current);
@@ -3567,8 +3572,10 @@ void exit_io_context(void) 


	if (ioc->aic && ioc->aic->exit)

		ioc->aic->exit(ioc->aic);

	if (ioc->cic && ioc->cic->exit)

		ioc->cic->exit(ioc->cic);

	if (ioc->cic_root.rb_node != NULL) {

		cic = rb_entry(rb_first(&ioc->cic_root), struct cfq_io_context, rb_node);

		cic->exit(ioc);

	}

 

	put_io_context(ioc);

}
@@ -3598,7 +3605,7 @@ struct io_context *current_io_context(gfp_t gfp_flags) 
		ret->last_waited = jiffies; /* doesn't matter... */

		ret->nr_batch_requests = 0; /* because this is 0 */

		ret->aic = NULL;

		ret->cic = NULL;

		ret->cic_root.rb_node = NULL;

		tsk->io_context = ret;

	}

include/linux/blkdev.h

+6 −8
Original line number Diff line number Diff line
@@ -55,13 +55,11 @@ struct as_io_context { 


struct cfq_queue;

struct cfq_io_context {

	/*

	 * circular list of cfq_io_contexts belonging to a process io context

	 */

	struct list_head list;

	struct cfq_queue *cfqq[2];

	struct rb_node rb_node;

	void *key;



	struct cfq_queue *cfqq[2];



	struct io_context *ioc;



	unsigned long last_end_request;
@@ -72,8 +70,8 @@ struct cfq_io_context { 


	struct list_head queue_list;



	void (*dtor)(struct cfq_io_context *);

	void (*exit)(struct cfq_io_context *);

	void (*dtor)(struct io_context *); /* destructor */

	void (*exit)(struct io_context *); /* called on task exit */

};



/*
@@ -94,7 +92,7 @@ struct io_context { 
	int nr_batch_requests;     /* Number of requests left in the batch */



	struct as_io_context *aic;

	struct cfq_io_context *cic;

	struct rb_root cic_root;

};



void put_io_context(struct io_context *ioc);