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[PATCH] [BLOCK] cfq-iosched: change cfq io context linking from list …
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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>
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Jens Axboe committed Mar 28, 2006
1 parent 329b10b commit e2d74ac
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Showing 3 changed files with 114 additions and 124 deletions.
205 changes: 95 additions & 110 deletions block/cfq-iosched.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1190,28 +1190,27 @@ 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);
}

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);
}

/*
Expand Down Expand Up @@ -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 *
Expand All @@ -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;
Expand Down Expand Up @@ -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);

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);

Expand Down Expand Up @@ -1445,14 +1446,67 @@ cfq_get_queue(struct cfq_data *cfqd, unsigned int key, struct task_struct *tsk,
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;
Expand All @@ -1463,88 +1517,15 @@ cfq_get_io_context(struct cfq_data *cfqd, pid_t pid, gfp_t gfp_mask)
if (!ioc)
return NULL;

restart:
if ((cic = ioc->cic) == NULL) {
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;
}
}
cic = cfq_cic_rb_lookup(cfqd, ioc);
if (cic)
goto out;

/*
* 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;
}
cic = cfq_alloc_io_context(cfqd, gfp_mask);
if (cic == NULL)
goto err;

cfq_cic_link(cfqd, ioc, cic);
out:
return cic;
err:
Expand Down Expand Up @@ -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);

Expand Down Expand Up @@ -2133,11 +2114,14 @@ 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)) {

while (!list_empty(&cfqd->cic_list)) {
struct cfq_io_context *cic = list_entry(cfqd->cic_list.next,
struct cfq_io_context,
queue_list);
Expand All @@ -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);

Expand Down
19 changes: 13 additions & 6 deletions block/ll_rw_blk.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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);
Expand All @@ -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);
Expand All @@ -3567,9 +3572,11 @@ 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);
}

Expand Down Expand Up @@ -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;
}

Expand Down
14 changes: 6 additions & 8 deletions include/linux/blkdev.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand All @@ -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 */
};

/*
Expand All @@ -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);
Expand Down

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