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block: change the request allocation/congestion logic to be sync/async based 

This makes sure that we never wait on async IO for sync requests, instead
of doing the split on writes vs reads.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jens Axboe 2009-04-06 14:48:01 +02:00 committed by Linus Torvalds
parent 0221c81b1b
commit 1faa16d228
6 changed files with 100 additions and 82 deletions
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70
block/blk-core.c
View File

@ -484,11 +484,11 @@ static int blk_init_free_list(struct request_queue *q)
{
struct request_list *rl = &q->rq;
rl->count[READ] = rl->count[WRITE] = 0;
rl->starved[READ] = rl->starved[WRITE] = 0;
rl->count[BLK_RW_SYNC] = rl->count[BLK_RW_ASYNC] = 0;
rl->starved[BLK_RW_SYNC] = rl->starved[BLK_RW_ASYNC] = 0;
rl->elvpriv = 0;
init_waitqueue_head(&rl->wait[READ]);
init_waitqueue_head(&rl->wait[WRITE]);
init_waitqueue_head(&rl->wait[BLK_RW_SYNC]);
init_waitqueue_head(&rl->wait[BLK_RW_ASYNC]);
rl->rq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
mempool_free_slab, request_cachep, q->node);
@ -699,18 +699,18 @@ static void ioc_set_batching(struct request_queue *q, struct io_context *ioc)
ioc->last_waited = jiffies;
}
static void __freed_request(struct request_queue *q, int rw)
static void __freed_request(struct request_queue *q, int sync)
{
struct request_list *rl = &q->rq;
if (rl->count[rw] < queue_congestion_off_threshold(q))
blk_clear_queue_congested(q, rw);
if (rl->count[sync] < queue_congestion_off_threshold(q))
blk_clear_queue_congested(q, sync);
if (rl->count[rw] + 1 <= q->nr_requests) {
if (waitqueue_active(&rl->wait[rw]))
wake_up(&rl->wait[rw]);
if (rl->count[sync] + 1 <= q->nr_requests) {
if (waitqueue_active(&rl->wait[sync]))
wake_up(&rl->wait[sync]);
blk_clear_queue_full(q, rw);
blk_clear_queue_full(q, sync);
}
}
@ -718,18 +718,18 @@ static void __freed_request(struct request_queue *q, int rw)
* A request has just been released. Account for it, update the full and
* congestion status, wake up any waiters. Called under q->queue_lock.
*/
static void freed_request(struct request_queue *q, int rw, int priv)
static void freed_request(struct request_queue *q, int sync, int priv)
{
struct request_list *rl = &q->rq;
rl->count[rw]--;
rl->count[sync]--;
if (priv)
rl->elvpriv--;
__freed_request(q, rw);
__freed_request(q, sync);
if (unlikely(rl->starved[rw ^ 1]))
__freed_request(q, rw ^ 1);
if (unlikely(rl->starved[sync ^ 1]))
__freed_request(q, sync ^ 1);
}
/*
@ -743,15 +743,15 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
struct request *rq = NULL;
struct request_list *rl = &q->rq;
struct io_context *ioc = NULL;
const int rw = rw_flags & 0x01;
const bool is_sync = rw_is_sync(rw_flags) != 0;
int may_queue, priv;
may_queue = elv_may_queue(q, rw_flags);
if (may_queue == ELV_MQUEUE_NO)
goto rq_starved;
if (rl->count[rw]+1 >= queue_congestion_on_threshold(q)) {
if (rl->count[rw]+1 >= q->nr_requests) {
if (rl->count[is_sync]+1 >= queue_congestion_on_threshold(q)) {
if (rl->count[is_sync]+1 >= q->nr_requests) {
ioc = current_io_context(GFP_ATOMIC, q->node);
/*
* The queue will fill after this allocation, so set
@ -759,9 +759,9 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
* This process will be allowed to complete a batch of
* requests, others will be blocked.
*/
if (!blk_queue_full(q, rw)) {
if (!blk_queue_full(q, is_sync)) {
ioc_set_batching(q, ioc);
blk_set_queue_full(q, rw);
blk_set_queue_full(q, is_sync);
} else {
if (may_queue != ELV_MQUEUE_MUST
&& !ioc_batching(q, ioc)) {
@ -774,7 +774,7 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
}
}
}
blk_set_queue_congested(q, rw);
blk_set_queue_congested(q, is_sync);
}
/*
@ -782,11 +782,11 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
* limit of requests, otherwise we could have thousands of requests
* allocated with any setting of ->nr_requests
*/
if (rl->count[rw] >= (3 * q->nr_requests / 2))
if (rl->count[is_sync] >= (3 * q->nr_requests / 2))
goto out;
rl->count[rw]++;
rl->starved[rw] = 0;
rl->count[is_sync]++;
rl->starved[is_sync] = 0;
priv = !test_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
if (priv)
@ -804,7 +804,7 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
* wait queue, but this is pretty rare.
*/
spin_lock_irq(q->queue_lock);
freed_request(q, rw, priv);
freed_request(q, is_sync, priv);
/*
* in the very unlikely event that allocation failed and no
@ -814,8 +814,8 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
* rq mempool into READ and WRITE
*/
rq_starved:
if (unlikely(rl->count[rw] == 0))
rl->starved[rw] = 1;
if (unlikely(rl->count[is_sync] == 0))
rl->starved[is_sync] = 1;
goto out;
}
@ -829,7 +829,7 @@ rq_starved:
if (ioc_batching(q, ioc))
ioc->nr_batch_requests--;
trace_block_getrq(q, bio, rw);
trace_block_getrq(q, bio, rw_flags & 1);
out:
return rq;
}
@ -843,7 +843,7 @@ out:
static struct request *get_request_wait(struct request_queue *q, int rw_flags,
struct bio *bio)
{
const int rw = rw_flags & 0x01;
const bool is_sync = rw_is_sync(rw_flags) != 0;
struct request *rq;
rq = get_request(q, rw_flags, bio, GFP_NOIO);
@ -852,10 +852,10 @@ static struct request *get_request_wait(struct request_queue *q, int rw_flags,
struct io_context *ioc;
struct request_list *rl = &q->rq;
prepare_to_wait_exclusive(&rl->wait[rw], &wait,
prepare_to_wait_exclusive(&rl->wait[is_sync], &wait,
TASK_UNINTERRUPTIBLE);
trace_block_sleeprq(q, bio, rw);
trace_block_sleeprq(q, bio, rw_flags & 1);
__generic_unplug_device(q);
spin_unlock_irq(q->queue_lock);
@ -871,7 +871,7 @@ static struct request *get_request_wait(struct request_queue *q, int rw_flags,
ioc_set_batching(q, ioc);
spin_lock_irq(q->queue_lock);
finish_wait(&rl->wait[rw], &wait);
finish_wait(&rl->wait[is_sync], &wait);
rq = get_request(q, rw_flags, bio, GFP_NOIO);
};
@ -1070,14 +1070,14 @@ void __blk_put_request(struct request_queue *q, struct request *req)
* it didn't come out of our reserved rq pools
*/
if (req->cmd_flags & REQ_ALLOCED) {
int rw = rq_data_dir(req);
int is_sync = rq_is_sync(req) != 0;
int priv = req->cmd_flags & REQ_ELVPRIV;
BUG_ON(!list_empty(&req->queuelist));
BUG_ON(!hlist_unhashed(&req->hash));
blk_free_request(q, req);
freed_request(q, rw, priv);
freed_request(q, is_sync, priv);
}
}
EXPORT_SYMBOL_GPL(__blk_put_request);

36
block/blk-sysfs.c
View File

@ -48,28 +48,28 @@ queue_requests_store(struct request_queue *q, const char *page, size_t count)
q->nr_requests = nr;
blk_queue_congestion_threshold(q);
if (rl->count[READ] >= queue_congestion_on_threshold(q))
blk_set_queue_congested(q, READ);
else if (rl->count[READ] < queue_congestion_off_threshold(q))
blk_clear_queue_congested(q, READ);
if (rl->count[BLK_RW_SYNC] >= queue_congestion_on_threshold(q))
blk_set_queue_congested(q, BLK_RW_SYNC);
else if (rl->count[BLK_RW_SYNC] < queue_congestion_off_threshold(q))
blk_clear_queue_congested(q, BLK_RW_SYNC);
if (rl->count[WRITE] >= queue_congestion_on_threshold(q))
blk_set_queue_congested(q, WRITE);
else if (rl->count[WRITE] < queue_congestion_off_threshold(q))
blk_clear_queue_congested(q, WRITE);
if (rl->count[BLK_RW_ASYNC] >= queue_congestion_on_threshold(q))
blk_set_queue_congested(q, BLK_RW_ASYNC);
else if (rl->count[BLK_RW_ASYNC] < queue_congestion_off_threshold(q))
blk_clear_queue_congested(q, BLK_RW_ASYNC);
if (rl->count[READ] >= q->nr_requests) {
blk_set_queue_full(q, READ);
} else if (rl->count[READ]+1 <= q->nr_requests) {
blk_clear_queue_full(q, READ);
wake_up(&rl->wait[READ]);
if (rl->count[BLK_RW_SYNC] >= q->nr_requests) {
blk_set_queue_full(q, BLK_RW_SYNC);
} else if (rl->count[BLK_RW_SYNC]+1 <= q->nr_requests) {
blk_clear_queue_full(q, BLK_RW_SYNC);
wake_up(&rl->wait[BLK_RW_SYNC]);
}
if (rl->count[WRITE] >= q->nr_requests) {
blk_set_queue_full(q, WRITE);
} else if (rl->count[WRITE]+1 <= q->nr_requests) {
blk_clear_queue_full(q, WRITE);
wake_up(&rl->wait[WRITE]);
if (rl->count[BLK_RW_ASYNC] >= q->nr_requests) {
blk_set_queue_full(q, BLK_RW_ASYNC);
} else if (rl->count[BLK_RW_ASYNC]+1 <= q->nr_requests) {
blk_clear_queue_full(q, BLK_RW_ASYNC);
wake_up(&rl->wait[BLK_RW_ASYNC]);
}
spin_unlock_irq(q->queue_lock);
return ret;

2
block/elevator.c
View File

@ -677,7 +677,7 @@ void elv_insert(struct request_queue *q, struct request *rq, int where)
}
if (unplug_it && blk_queue_plugged(q)) {
int nrq = q->rq.count[READ] + q->rq.count[WRITE]
int nrq = q->rq.count[BLK_RW_SYNC] + q->rq.count[BLK_RW_ASYNC]
- q->in_flight;
if (nrq >= q->unplug_thresh)

12
include/linux/backing-dev.h
View File

@ -24,8 +24,8 @@ struct dentry;
*/
enum bdi_state {
BDI_pdflush, /* A pdflush thread is working this device */
BDI_write_congested, /* The write queue is getting full */
BDI_read_congested, /* The read queue is getting full */
BDI_async_congested, /* The async (write) queue is getting full */
BDI_sync_congested, /* The sync queue is getting full */
BDI_unused, /* Available bits start here */
};
@ -215,18 +215,18 @@ static inline int bdi_congested(struct backing_dev_info *bdi, int bdi_bits)
static inline int bdi_read_congested(struct backing_dev_info *bdi)
{
return bdi_congested(bdi, 1 << BDI_read_congested);
return bdi_congested(bdi, 1 << BDI_sync_congested);
}
static inline int bdi_write_congested(struct backing_dev_info *bdi)
{
return bdi_congested(bdi, 1 << BDI_write_congested);
return bdi_congested(bdi, 1 << BDI_async_congested);
}
static inline int bdi_rw_congested(struct backing_dev_info *bdi)
{
return bdi_congested(bdi, (1 << BDI_read_congested)|
(1 << BDI_write_congested));
return bdi_congested(bdi, (1 << BDI_sync_congested) |
(1 << BDI_async_congested));
}
void clear_bdi_congested(struct backing_dev_info *bdi, int rw);

52
include/linux/blkdev.h
View File

@ -38,6 +38,10 @@ struct request;
typedef void (rq_end_io_fn)(struct request *, int);
struct request_list {
/*
* count[], starved[], and wait[] are indexed by
* BLK_RW_SYNC/BLK_RW_ASYNC
*/
int count[2];
int starved[2];
int elvpriv;
@ -66,6 +70,11 @@ enum rq_cmd_type_bits {
REQ_TYPE_ATA_PC,
};
enum {
BLK_RW_ASYNC = 0,
BLK_RW_SYNC = 1,
};
/*
* For request of type REQ_TYPE_LINUX_BLOCK, rq->cmd[0] is the opcode being
* sent down (similar to how REQ_TYPE_BLOCK_PC means that ->cmd[] holds a
@ -103,7 +112,7 @@ enum rq_flag_bits {
__REQ_QUIET, /* don't worry about errors */
__REQ_PREEMPT, /* set for "ide_preempt" requests */
__REQ_ORDERED_COLOR, /* is before or after barrier */
__REQ_RW_SYNC, /* request is sync (O_DIRECT) */
__REQ_RW_SYNC, /* request is sync (sync write or read) */
__REQ_ALLOCED, /* request came from our alloc pool */
__REQ_RW_META, /* metadata io request */
__REQ_COPY_USER, /* contains copies of user pages */
@ -438,8 +447,8 @@ struct request_queue
#define QUEUE_FLAG_CLUSTER 0 /* cluster several segments into 1 */
#define QUEUE_FLAG_QUEUED 1 /* uses generic tag queueing */
#define QUEUE_FLAG_STOPPED 2 /* queue is stopped */
#define QUEUE_FLAG_READFULL 3 /* read queue has been filled */
#define QUEUE_FLAG_WRITEFULL 4 /* write queue has been filled */
#define QUEUE_FLAG_SYNCFULL 3 /* read queue has been filled */
#define QUEUE_FLAG_ASYNCFULL 4 /* write queue has been filled */
#define QUEUE_FLAG_DEAD 5 /* queue being torn down */
#define QUEUE_FLAG_REENTER 6 /* Re-entrancy avoidance */
#define QUEUE_FLAG_PLUGGED 7 /* queue is plugged */
@ -611,32 +620,41 @@ enum {
#define rq_data_dir(rq) ((rq)->cmd_flags & 1)
/*
* We regard a request as sync, if it's a READ or a SYNC write.
* We regard a request as sync, if either a read or a sync write
*/
#define rq_is_sync(rq) (rq_data_dir((rq)) == READ || (rq)->cmd_flags & REQ_RW_SYNC)
static inline bool rw_is_sync(unsigned int rw_flags)
{
return !(rw_flags & REQ_RW) || (rw_flags & REQ_RW_SYNC);
}
static inline bool rq_is_sync(struct request *rq)
{
return rw_is_sync(rq->cmd_flags);
}
#define rq_is_meta(rq) ((rq)->cmd_flags & REQ_RW_META)
static inline int blk_queue_full(struct request_queue *q, int rw)
static inline int blk_queue_full(struct request_queue *q, int sync)
{
if (rw == READ)
return test_bit(QUEUE_FLAG_READFULL, &q->queue_flags);
return test_bit(QUEUE_FLAG_WRITEFULL, &q->queue_flags);
if (sync)
return test_bit(QUEUE_FLAG_SYNCFULL, &q->queue_flags);
return test_bit(QUEUE_FLAG_ASYNCFULL, &q->queue_flags);
}
static inline void blk_set_queue_full(struct request_queue *q, int rw)
static inline void blk_set_queue_full(struct request_queue *q, int sync)
{
if (rw == READ)
queue_flag_set(QUEUE_FLAG_READFULL, q);
if (sync)
queue_flag_set(QUEUE_FLAG_SYNCFULL, q);
else
queue_flag_set(QUEUE_FLAG_WRITEFULL, q);
queue_flag_set(QUEUE_FLAG_ASYNCFULL, q);
}
static inline void blk_clear_queue_full(struct request_queue *q, int rw)
static inline void blk_clear_queue_full(struct request_queue *q, int sync)
{
if (rw == READ)
queue_flag_clear(QUEUE_FLAG_READFULL, q);
if (sync)
queue_flag_clear(QUEUE_FLAG_SYNCFULL, q);
else
queue_flag_clear(QUEUE_FLAG_WRITEFULL, q);
queue_flag_clear(QUEUE_FLAG_ASYNCFULL, q);
}

10
mm/backing-dev.c
View File

@ -284,12 +284,12 @@ static wait_queue_head_t congestion_wqh[2] = {
};
void clear_bdi_congested(struct backing_dev_info *bdi, int rw)
void clear_bdi_congested(struct backing_dev_info *bdi, int sync)
{
enum bdi_state bit;
wait_queue_head_t *wqh = &congestion_wqh[rw];
wait_queue_head_t *wqh = &congestion_wqh[sync];
bit = (rw == WRITE) ? BDI_write_congested : BDI_read_congested;
bit = sync ? BDI_sync_congested : BDI_async_congested;
clear_bit(bit, &bdi->state);
smp_mb__after_clear_bit();
if (waitqueue_active(wqh))
@ -297,11 +297,11 @@ void clear_bdi_congested(struct backing_dev_info *bdi, int rw)
}
EXPORT_SYMBOL(clear_bdi_congested);
void set_bdi_congested(struct backing_dev_info *bdi, int rw)
void set_bdi_congested(struct backing_dev_info *bdi, int sync)
{
enum bdi_state bit;
bit = (rw == WRITE) ? BDI_write_congested : BDI_read_congested;
bit = sync ? BDI_sync_congested : BDI_async_congested;
set_bit(bit, &bdi->state);
}
EXPORT_SYMBOL(set_bdi_congested);