[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>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index bde40a6..bb43a16 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1190,19 +1190,19 @@
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_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 @@
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 @@
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 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);
-
- list_for_each_entry(cic, &cic->list, list)
+ n = rb_first(&ioc->cic_root);
+ while (n != NULL) {
+ cic = rb_entry(n, struct cfq_io_context, rb_node);
+
changed_ioprio(cic);
+ n = rb_next(n);
+ }
write_unlock(&cfq_exit_lock);
@@ -1445,14 +1446,67 @@
return cfqq;
}
+static struct cfq_io_context *
+cfq_cic_rb_lookup(struct cfq_data *cfqd, struct io_context *ioc)
+{
+ struct rb_node *n = ioc->cic_root.rb_node;
+ struct cfq_io_context *cic;
+ void *key = cfqd;
+
+ 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;
+ }
+
+ return NULL;
+}
+
+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;
+
+ read_lock(&cfq_exit_lock);
+
+ cic->ioc = ioc;
+ cic->key = cfqd;
+
+ ioc->set_ioprio = cfq_ioc_set_ioprio;
+
+ while (*p) {
+ parent = *p;
+ __cic = rb_entry(parent, struct cfq_io_context, rb_node);
+
+ if (cic->key < __cic->key)
+ p = &(*p)->rb_left;
+ else if (cic->key > __cic->key)
+ p = &(*p)->rb_right;
+ else
+ BUG();
+ }
+
+ 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);
+}
+
/*
* 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
+ * than one device managed by cfq.
*/
static struct cfq_io_context *
-cfq_get_io_context(struct cfq_data *cfqd, pid_t pid, gfp_t gfp_mask)
+cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
{
struct io_context *ioc = NULL;
struct cfq_io_context *cic;
@@ -1463,88 +1517,15 @@
if (!ioc)
return NULL;
-restart:
- if ((cic = ioc->cic) == NULL) {
- cic = cfq_alloc_io_context(cfqd, gfp_mask);
+ cic = cfq_cic_rb_lookup(cfqd, ioc);
+ if (cic)
+ goto out;
- if (cic == NULL)
- goto err;
+ cic = cfq_alloc_io_context(cfqd, gfp_mask);
+ if (cic == NULL)
+ goto err;
- /*
- * 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;
-
- if (unlikely(!cic->key)) {
- read_lock(&cfq_exit_lock);
- if (list_empty(&cic->list))
- ioc->cic = NULL;
- 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;
- }
-
- /*
- * 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);
- 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
- */
- __cic = cfq_alloc_io_context(cfqd, gfp_mask);
- if (__cic == NULL)
- goto err;
-
- __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;
- }
-
+ cfq_cic_link(cfqd, ioc, cic);
out:
return cic;
err:
@@ -1965,7 +1946,7 @@
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);
@@ -2133,11 +2114,14 @@
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)) {
+
+ while (!list_empty(&cfqd->cic_list)) {
struct cfq_io_context *cic = list_entry(cfqd->cic_list.next,
struct cfq_io_context,
queue_list);
@@ -2152,6 +2136,7 @@
cic->key = NULL;
list_del_init(&cic->queue_list);
}
+
spin_unlock_irq(q->queue_lock);
write_unlock(&cfq_exit_lock);
