block: change the request allocation/congestion logic to be sync/async based
Jens Axboe [Mon, 6 Apr 2009 12:48:01 +0000 (14:48 +0200)]
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>

block/blk-core.c
block/blk-sysfs.c
block/elevator.c
include/linux/backing-dev.h
include/linux/blkdev.h
mm/backing-dev.c

index 996ed90..a32b571 100644 (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);
index e29ddfc..3ff9bba 100644 (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[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[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] >= 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[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[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;
index 98259ed..ca6788a 100644 (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)
index bee52ab..0ec2c59 100644 (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);
index 465d6ba..67dae3b 100644 (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);
 }
 
 
index be68c95..493b468 100644 (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);