[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: Jens Axboe <axboe@suse.de>
This commit is contained in:
Jens Axboe
parent
329b10bb0f
commit
e2d74ac066
@ -1190,19 +1190,19 @@ cfq_find_cfq_hash(struct cfq_data *cfqd, unsigned int key, unsigned short prio)
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return __cfq_find_cfq_hash(cfqd, key, prio, hash_long(key, CFQ_QHASH_SHIFT));
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}
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static void cfq_free_io_context(struct cfq_io_context *cic)
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static void cfq_free_io_context(struct io_context *ioc)
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{
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struct cfq_io_context *__cic;
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struct list_head *entry, *next;
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int freed = 1;
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struct rb_node *n;
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int freed = 0;
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list_for_each_safe(entry, next, &cic->list) {
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__cic = list_entry(entry, struct cfq_io_context, list);
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while ((n = rb_first(&ioc->cic_root)) != NULL) {
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__cic = rb_entry(n, struct cfq_io_context, rb_node);
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rb_erase(&__cic->rb_node, &ioc->cic_root);
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kmem_cache_free(cfq_ioc_pool, __cic);
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freed++;
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}
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kmem_cache_free(cfq_ioc_pool, cic);
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if (atomic_sub_and_test(freed, &ioc_count) && ioc_gone)
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complete(ioc_gone);
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}
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@ -1210,8 +1210,7 @@ static void cfq_free_io_context(struct cfq_io_context *cic)
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static void cfq_trim(struct io_context *ioc)
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{
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ioc->set_ioprio = NULL;
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if (ioc->cic)
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cfq_free_io_context(ioc->cic);
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cfq_free_io_context(ioc);
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}
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/*
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@ -1250,26 +1249,26 @@ static void cfq_exit_single_io_context(struct cfq_io_context *cic)
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spin_unlock(q->queue_lock);
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}
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static void cfq_exit_io_context(struct cfq_io_context *cic)
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static void cfq_exit_io_context(struct io_context *ioc)
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{
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struct cfq_io_context *__cic;
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struct list_head *entry;
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unsigned long flags;
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local_irq_save(flags);
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struct rb_node *n;
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/*
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* put the reference this task is holding to the various queues
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*/
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read_lock(&cfq_exit_lock);
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list_for_each(entry, &cic->list) {
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__cic = list_entry(entry, struct cfq_io_context, list);
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read_lock_irqsave(&cfq_exit_lock, flags);
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n = rb_first(&ioc->cic_root);
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while (n != NULL) {
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__cic = rb_entry(n, struct cfq_io_context, rb_node);
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cfq_exit_single_io_context(__cic);
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n = rb_next(n);
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}
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cfq_exit_single_io_context(cic);
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read_unlock(&cfq_exit_lock);
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local_irq_restore(flags);
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read_unlock_irqrestore(&cfq_exit_lock, flags);
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}
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static struct cfq_io_context *
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@ -1278,10 +1277,10 @@ cfq_alloc_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
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struct cfq_io_context *cic = kmem_cache_alloc(cfq_ioc_pool, gfp_mask);
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if (cic) {
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INIT_LIST_HEAD(&cic->list);
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RB_CLEAR(&cic->rb_node);
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cic->key = NULL;
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cic->cfqq[ASYNC] = NULL;
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cic->cfqq[SYNC] = NULL;
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cic->key = NULL;
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cic->last_end_request = jiffies;
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cic->ttime_total = 0;
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cic->ttime_samples = 0;
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@ -1373,15 +1372,17 @@ static inline void changed_ioprio(struct cfq_io_context *cic)
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static int cfq_ioc_set_ioprio(struct io_context *ioc, unsigned int ioprio)
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{
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struct cfq_io_context *cic;
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struct rb_node *n;
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write_lock(&cfq_exit_lock);
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cic = ioc->cic;
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changed_ioprio(cic);
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list_for_each_entry(cic, &cic->list, list)
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n = rb_first(&ioc->cic_root);
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while (n != NULL) {
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cic = rb_entry(n, struct cfq_io_context, rb_node);
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changed_ioprio(cic);
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n = rb_next(n);
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}
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write_unlock(&cfq_exit_lock);
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@ -1445,14 +1446,67 @@ out:
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return cfqq;
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}
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static struct cfq_io_context *
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cfq_cic_rb_lookup(struct cfq_data *cfqd, struct io_context *ioc)
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{
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struct rb_node *n = ioc->cic_root.rb_node;
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struct cfq_io_context *cic;
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void *key = cfqd;
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while (n) {
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cic = rb_entry(n, struct cfq_io_context, rb_node);
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if (key < cic->key)
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n = n->rb_left;
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else if (key > cic->key)
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n = n->rb_right;
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else
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return cic;
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}
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return NULL;
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}
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static inline void
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cfq_cic_link(struct cfq_data *cfqd, struct io_context *ioc,
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struct cfq_io_context *cic)
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{
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struct rb_node **p = &ioc->cic_root.rb_node;
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struct rb_node *parent = NULL;
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struct cfq_io_context *__cic;
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read_lock(&cfq_exit_lock);
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cic->ioc = ioc;
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cic->key = cfqd;
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ioc->set_ioprio = cfq_ioc_set_ioprio;
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while (*p) {
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parent = *p;
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__cic = rb_entry(parent, struct cfq_io_context, rb_node);
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if (cic->key < __cic->key)
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p = &(*p)->rb_left;
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else if (cic->key > __cic->key)
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p = &(*p)->rb_right;
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else
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BUG();
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}
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rb_link_node(&cic->rb_node, parent, p);
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rb_insert_color(&cic->rb_node, &ioc->cic_root);
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list_add(&cic->queue_list, &cfqd->cic_list);
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read_unlock(&cfq_exit_lock);
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}
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/*
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* Setup general io context and cfq io context. There can be several cfq
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* io contexts per general io context, if this process is doing io to more
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* than one device managed by cfq. Note that caller is holding a reference to
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* cfqq, so we don't need to worry about it disappearing
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* than one device managed by cfq.
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*/
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static struct cfq_io_context *
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cfq_get_io_context(struct cfq_data *cfqd, pid_t pid, gfp_t gfp_mask)
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cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
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{
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struct io_context *ioc = NULL;
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struct cfq_io_context *cic;
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@ -1463,88 +1517,15 @@ cfq_get_io_context(struct cfq_data *cfqd, pid_t pid, gfp_t gfp_mask)
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if (!ioc)
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return NULL;
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restart:
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if ((cic = ioc->cic) == NULL) {
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cic = cfq_alloc_io_context(cfqd, gfp_mask);
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cic = cfq_cic_rb_lookup(cfqd, ioc);
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if (cic)
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goto out;
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if (cic == NULL)
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goto err;
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/*
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* manually increment generic io_context usage count, it
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* cannot go away since we are already holding one ref to it
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*/
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cic->ioc = ioc;
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cic->key = cfqd;
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read_lock(&cfq_exit_lock);
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ioc->set_ioprio = cfq_ioc_set_ioprio;
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ioc->cic = cic;
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list_add(&cic->queue_list, &cfqd->cic_list);
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read_unlock(&cfq_exit_lock);
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} else {
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struct cfq_io_context *__cic;
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/*
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* the first cic on the list is actually the head itself
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*/
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if (cic->key == cfqd)
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goto out;
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if (unlikely(!cic->key)) {
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read_lock(&cfq_exit_lock);
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if (list_empty(&cic->list))
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ioc->cic = NULL;
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else
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ioc->cic = list_entry(cic->list.next,
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struct cfq_io_context,
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list);
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read_unlock(&cfq_exit_lock);
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kmem_cache_free(cfq_ioc_pool, cic);
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atomic_dec(&ioc_count);
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goto restart;
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}
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/*
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* cic exists, check if we already are there. linear search
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* should be ok here, the list will usually not be more than
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* 1 or a few entries long
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*/
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list_for_each_entry(__cic, &cic->list, list) {
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/*
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* this process is already holding a reference to
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* this queue, so no need to get one more
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*/
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if (__cic->key == cfqd) {
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cic = __cic;
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goto out;
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}
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if (unlikely(!__cic->key)) {
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read_lock(&cfq_exit_lock);
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list_del(&__cic->list);
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read_unlock(&cfq_exit_lock);
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kmem_cache_free(cfq_ioc_pool, __cic);
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atomic_dec(&ioc_count);
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goto restart;
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}
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}
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/*
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* nope, process doesn't have a cic assoicated with this
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* cfqq yet. get a new one and add to list
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*/
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__cic = cfq_alloc_io_context(cfqd, gfp_mask);
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if (__cic == NULL)
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goto err;
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__cic->ioc = ioc;
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__cic->key = cfqd;
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read_lock(&cfq_exit_lock);
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list_add(&__cic->list, &cic->list);
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list_add(&__cic->queue_list, &cfqd->cic_list);
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read_unlock(&cfq_exit_lock);
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cic = __cic;
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}
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cic = cfq_alloc_io_context(cfqd, gfp_mask);
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if (cic == NULL)
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goto err;
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cfq_cic_link(cfqd, ioc, cic);
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out:
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return cic;
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err:
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@ -1965,7 +1946,7 @@ cfq_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
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might_sleep_if(gfp_mask & __GFP_WAIT);
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cic = cfq_get_io_context(cfqd, key, gfp_mask);
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cic = cfq_get_io_context(cfqd, gfp_mask);
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spin_lock_irqsave(q->queue_lock, flags);
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@ -2133,11 +2114,14 @@ static void cfq_exit_queue(elevator_t *e)
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request_queue_t *q = cfqd->queue;
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cfq_shutdown_timer_wq(cfqd);
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write_lock(&cfq_exit_lock);
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spin_lock_irq(q->queue_lock);
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if (cfqd->active_queue)
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__cfq_slice_expired(cfqd, cfqd->active_queue, 0);
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while(!list_empty(&cfqd->cic_list)) {
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while (!list_empty(&cfqd->cic_list)) {
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struct cfq_io_context *cic = list_entry(cfqd->cic_list.next,
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struct cfq_io_context,
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queue_list);
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@ -2152,6 +2136,7 @@ static void cfq_exit_queue(elevator_t *e)
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cic->key = NULL;
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list_del_init(&cic->queue_list);
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}
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spin_unlock_irq(q->queue_lock);
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write_unlock(&cfq_exit_lock);
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@ -3539,11 +3539,15 @@ void put_io_context(struct io_context *ioc)
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BUG_ON(atomic_read(&ioc->refcount) == 0);
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if (atomic_dec_and_test(&ioc->refcount)) {
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struct cfq_io_context *cic;
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rcu_read_lock();
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if (ioc->aic && ioc->aic->dtor)
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ioc->aic->dtor(ioc->aic);
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if (ioc->cic && ioc->cic->dtor)
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ioc->cic->dtor(ioc->cic);
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if (ioc->cic_root.rb_node != NULL) {
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cic = rb_entry(rb_first(&ioc->cic_root), struct cfq_io_context, rb_node);
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cic->dtor(ioc);
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}
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rcu_read_unlock();
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kmem_cache_free(iocontext_cachep, ioc);
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@ -3556,6 +3560,7 @@ void exit_io_context(void)
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{
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unsigned long flags;
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struct io_context *ioc;
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struct cfq_io_context *cic;
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local_irq_save(flags);
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task_lock(current);
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@ -3567,9 +3572,11 @@ void exit_io_context(void)
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if (ioc->aic && ioc->aic->exit)
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ioc->aic->exit(ioc->aic);
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if (ioc->cic && ioc->cic->exit)
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ioc->cic->exit(ioc->cic);
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if (ioc->cic_root.rb_node != NULL) {
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cic = rb_entry(rb_first(&ioc->cic_root), struct cfq_io_context, rb_node);
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cic->exit(ioc);
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}
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put_io_context(ioc);
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}
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@ -3598,7 +3605,7 @@ struct io_context *current_io_context(gfp_t gfp_flags)
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ret->last_waited = jiffies; /* doesn't matter... */
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ret->nr_batch_requests = 0; /* because this is 0 */
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ret->aic = NULL;
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ret->cic = NULL;
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ret->cic_root.rb_node = NULL;
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tsk->io_context = ret;
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}
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@ -55,13 +55,11 @@ struct as_io_context {
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struct cfq_queue;
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struct cfq_io_context {
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/*
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* circular list of cfq_io_contexts belonging to a process io context
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*/
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struct list_head list;
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struct cfq_queue *cfqq[2];
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struct rb_node rb_node;
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void *key;
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struct cfq_queue *cfqq[2];
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struct io_context *ioc;
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unsigned long last_end_request;
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@ -72,8 +70,8 @@ struct cfq_io_context {
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struct list_head queue_list;
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void (*dtor)(struct cfq_io_context *);
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void (*exit)(struct cfq_io_context *);
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void (*dtor)(struct io_context *); /* destructor */
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void (*exit)(struct io_context *); /* called on task exit */
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};
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/*
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@ -94,7 +92,7 @@ struct io_context {
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int nr_batch_requests; /* Number of requests left in the batch */
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struct as_io_context *aic;
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struct cfq_io_context *cic;
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struct rb_root cic_root;
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};
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void put_io_context(struct io_context *ioc);
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