[BLOCK] Reimplement elevator switch
This patch reimplements elevator switch. This patch assumes generic
dispatch queue patchset is applied.
* Each request is tagged with REQ_ELVPRIV flag if it has its elevator
private data set.
* Requests which doesn't have REQ_ELVPRIV flag set never enter
iosched. They are always directly back inserted to dispatch queue.
Of course, elevator_put_req_fn is called only for requests which
have its REQ_ELVPRIV set.
* Request queue maintains the current number of requests which have
its elevator data set (elevator_set_req_fn called) in
q->rq->elvpriv.
* If a request queue has QUEUE_FLAG_BYPASS set, elevator private data
is not allocated for new requests.
To switch to another iosched, we set QUEUE_FLAG_BYPASS and wait until
elvpriv goes to zero; then, we attach the new iosched and clears
QUEUE_FLAG_BYPASS. New implementation is much simpler and main code
paths are less cluttered, IMHO.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jens Axboe <axboe@suse.de>
diff --git a/drivers/block/ll_rw_blk.c b/drivers/block/ll_rw_blk.c
index d2a66fd..f7c9931 100644
--- a/drivers/block/ll_rw_blk.c
+++ b/drivers/block/ll_rw_blk.c
@@ -263,8 +263,6 @@
blk_queue_bounce_limit(q, BLK_BOUNCE_HIGH);
blk_queue_activity_fn(q, NULL, NULL);
-
- INIT_LIST_HEAD(&q->drain_list);
}
EXPORT_SYMBOL(blk_queue_make_request);
@@ -1050,6 +1048,7 @@
"REQ_STARTED",
"REQ_DONTPREP",
"REQ_QUEUED",
+ "REQ_ELVPRIV",
"REQ_PC",
"REQ_BLOCK_PC",
"REQ_SENSE",
@@ -1640,9 +1639,9 @@
rl->count[READ] = rl->count[WRITE] = 0;
rl->starved[READ] = rl->starved[WRITE] = 0;
+ rl->elvpriv = 0;
init_waitqueue_head(&rl->wait[READ]);
init_waitqueue_head(&rl->wait[WRITE]);
- init_waitqueue_head(&rl->drain);
rl->rq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
mempool_free_slab, request_cachep, q->node);
@@ -1785,12 +1784,14 @@
static inline void blk_free_request(request_queue_t *q, struct request *rq)
{
- elv_put_request(q, rq);
+ if (rq->flags & REQ_ELVPRIV)
+ elv_put_request(q, rq);
mempool_free(rq, q->rq.rq_pool);
}
static inline struct request *
-blk_alloc_request(request_queue_t *q, int rw, struct bio *bio, int gfp_mask)
+blk_alloc_request(request_queue_t *q, int rw, struct bio *bio,
+ int priv, int gfp_mask)
{
struct request *rq = mempool_alloc(q->rq.rq_pool, gfp_mask);
@@ -1803,11 +1804,15 @@
*/
rq->flags = rw;
- if (!elv_set_request(q, rq, bio, gfp_mask))
- return rq;
+ if (priv) {
+ if (unlikely(elv_set_request(q, rq, bio, gfp_mask))) {
+ mempool_free(rq, q->rq.rq_pool);
+ return NULL;
+ }
+ rq->flags |= REQ_ELVPRIV;
+ }
- mempool_free(rq, q->rq.rq_pool);
- return NULL;
+ return rq;
}
/*
@@ -1863,22 +1868,18 @@
* 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(request_queue_t *q, int rw)
+static void freed_request(request_queue_t *q, int rw, int priv)
{
struct request_list *rl = &q->rq;
rl->count[rw]--;
+ if (priv)
+ rl->elvpriv--;
__freed_request(q, rw);
if (unlikely(rl->starved[rw ^ 1]))
__freed_request(q, rw ^ 1);
-
- if (!rl->count[READ] && !rl->count[WRITE]) {
- smp_mb();
- if (unlikely(waitqueue_active(&rl->drain)))
- wake_up(&rl->drain);
- }
}
#define blkdev_free_rq(list) list_entry((list)->next, struct request, queuelist)
@@ -1893,9 +1894,7 @@
struct request *rq = NULL;
struct request_list *rl = &q->rq;
struct io_context *ioc = current_io_context(GFP_ATOMIC);
-
- if (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags)))
- goto out;
+ int priv;
if (rl->count[rw]+1 >= q->nr_requests) {
/*
@@ -1940,9 +1939,14 @@
rl->starved[rw] = 0;
if (rl->count[rw] >= queue_congestion_on_threshold(q))
set_queue_congested(q, rw);
+
+ priv = !test_bit(QUEUE_FLAG_BYPASS, &q->queue_flags);
+ if (priv)
+ rl->elvpriv++;
+
spin_unlock_irq(q->queue_lock);
- rq = blk_alloc_request(q, rw, bio, gfp_mask);
+ rq = blk_alloc_request(q, rw, bio, priv, gfp_mask);
if (!rq) {
/*
* Allocation failed presumably due to memory. Undo anything
@@ -1952,7 +1956,7 @@
* wait queue, but this is pretty rare.
*/
spin_lock_irq(q->queue_lock);
- freed_request(q, rw);
+ freed_request(q, rw, priv);
/*
* in the very unlikely event that allocation failed and no
@@ -2470,11 +2474,12 @@
*/
if (rl) {
int rw = rq_data_dir(req);
+ int priv = req->flags & REQ_ELVPRIV;
BUG_ON(!list_empty(&req->queuelist));
blk_free_request(q, req);
- freed_request(q, rw);
+ freed_request(q, rw, priv);
}
}
@@ -2802,97 +2807,6 @@
}
}
-void blk_finish_queue_drain(request_queue_t *q)
-{
- struct request_list *rl = &q->rq;
- struct request *rq;
- int requeued = 0;
-
- spin_lock_irq(q->queue_lock);
- clear_bit(QUEUE_FLAG_DRAIN, &q->queue_flags);
-
- while (!list_empty(&q->drain_list)) {
- rq = list_entry_rq(q->drain_list.next);
-
- list_del_init(&rq->queuelist);
- elv_requeue_request(q, rq);
- requeued++;
- }
-
- if (requeued)
- q->request_fn(q);
-
- spin_unlock_irq(q->queue_lock);
-
- wake_up(&rl->wait[0]);
- wake_up(&rl->wait[1]);
- wake_up(&rl->drain);
-}
-
-static int wait_drain(request_queue_t *q, struct request_list *rl, int dispatch)
-{
- int wait = rl->count[READ] + rl->count[WRITE];
-
- if (dispatch)
- wait += !list_empty(&q->queue_head);
-
- return wait;
-}
-
-/*
- * We rely on the fact that only requests allocated through blk_alloc_request()
- * have io scheduler private data structures associated with them. Any other
- * type of request (allocated on stack or through kmalloc()) should not go
- * to the io scheduler core, but be attached to the queue head instead.
- */
-void blk_wait_queue_drained(request_queue_t *q, int wait_dispatch)
-{
- struct request_list *rl = &q->rq;
- DEFINE_WAIT(wait);
-
- spin_lock_irq(q->queue_lock);
- set_bit(QUEUE_FLAG_DRAIN, &q->queue_flags);
-
- while (wait_drain(q, rl, wait_dispatch)) {
- prepare_to_wait(&rl->drain, &wait, TASK_UNINTERRUPTIBLE);
-
- if (wait_drain(q, rl, wait_dispatch)) {
- __generic_unplug_device(q);
- spin_unlock_irq(q->queue_lock);
- io_schedule();
- spin_lock_irq(q->queue_lock);
- }
-
- finish_wait(&rl->drain, &wait);
- }
-
- spin_unlock_irq(q->queue_lock);
-}
-
-/*
- * block waiting for the io scheduler being started again.
- */
-static inline void block_wait_queue_running(request_queue_t *q)
-{
- DEFINE_WAIT(wait);
-
- while (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags))) {
- struct request_list *rl = &q->rq;
-
- prepare_to_wait_exclusive(&rl->drain, &wait,
- TASK_UNINTERRUPTIBLE);
-
- /*
- * re-check the condition. avoids using prepare_to_wait()
- * in the fast path (queue is running)
- */
- if (test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags))
- io_schedule();
-
- finish_wait(&rl->drain, &wait);
- }
-}
-
static void handle_bad_sector(struct bio *bio)
{
char b[BDEVNAME_SIZE];
@@ -2988,8 +2902,6 @@
if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
goto end_io;
- block_wait_queue_running(q);
-
/*
* If this device has partitions, remap block n
* of partition p to block n+start(p) of the disk.