Unlike other ioscheds, as-iosched handles alias by chaing them using
rq->queuelist. As aliased requests are very rare in the first place,
this complicates merge/dispatch handling without meaningful
performance improvement. This patch updates as-iosched to dump
aliased requests into dispatch queue as other ioscheds do.
Signed-off-by: Tejun Heo <[email protected]>
---
Jens, I've tested this change for several hours, but it might be
better to postpone this change to next release. It's your call.
diff --git a/block/as-iosched.c b/block/as-iosched.c
--- a/block/as-iosched.c
+++ b/block/as-iosched.c
@@ -184,6 +184,9 @@ struct as_rq {
static kmem_cache_t *arq_pool;
+static void as_move_to_dispatch(struct as_data *ad, struct as_rq *arq);
+static void as_antic_stop(struct as_data *ad);
+
/*
* IO Context helper functions
*/
@@ -372,7 +375,7 @@ static struct as_rq *as_find_first_arq(s
* existing request against the same sector), which can happen when using
* direct IO, then return the alias.
*/
-static struct as_rq *as_add_arq_rb(struct as_data *ad, struct as_rq *arq)
+static struct as_rq *__as_add_arq_rb(struct as_data *ad, struct as_rq *arq)
{
struct rb_node **p = &ARQ_RB_ROOT(ad, arq)->rb_node;
struct rb_node *parent = NULL;
@@ -399,6 +402,16 @@ static struct as_rq *as_add_arq_rb(struc
return NULL;
}
+static void as_add_arq_rb(struct as_data *ad, struct as_rq *arq)
+{
+ struct as_rq *alias;
+
+ while ((unlikely(alias = __as_add_arq_rb(ad, arq)))) {
+ as_move_to_dispatch(ad, alias);
+ as_antic_stop(ad);
+ }
+}
+
static inline void as_del_arq_rb(struct as_data *ad, struct as_rq *arq)
{
if (!ON_RB(&arq->rb_node)) {
@@ -1135,23 +1148,6 @@ static void as_move_to_dispatch(struct a
/*
* take it off the sort and fifo list, add to dispatch queue
*/
- while (!list_empty(&rq->queuelist)) {
- struct request *__rq = list_entry_rq(rq->queuelist.next);
- struct as_rq *__arq = RQ_DATA(__rq);
-
- list_del(&__rq->queuelist);
-
- elv_dispatch_add_tail(ad->q, __rq);
-
- if (__arq->io_context && __arq->io_context->aic)
- atomic_inc(&__arq->io_context->aic->nr_dispatched);
-
- WARN_ON(__arq->state != AS_RQ_QUEUED);
- __arq->state = AS_RQ_DISPATCHED;
-
- ad->nr_dispatched++;
- }
-
as_remove_queued_request(ad->q, rq);
WARN_ON(arq->state != AS_RQ_QUEUED);
@@ -1328,49 +1324,12 @@ fifo_expired:
}
/*
- * Add arq to a list behind alias
- */
-static inline void
-as_add_aliased_request(struct as_data *ad, struct as_rq *arq,
- struct as_rq *alias)
-{
- struct request *req = arq->request;
- struct list_head *insert = alias->request->queuelist.prev;
-
- /*
- * Transfer list of aliases
- */
- while (!list_empty(&req->queuelist)) {
- struct request *__rq = list_entry_rq(req->queuelist.next);
- struct as_rq *__arq = RQ_DATA(__rq);
-
- list_move_tail(&__rq->queuelist, &alias->request->queuelist);
-
- WARN_ON(__arq->state != AS_RQ_QUEUED);
- }
-
- /*
- * Another request with the same start sector on the rbtree.
- * Link this request to that sector. They are untangled in
- * as_move_to_dispatch
- */
- list_add(&arq->request->queuelist, insert);
-
- /*
- * Don't want to have to handle merges.
- */
- as_del_arq_hash(arq);
- arq->request->flags |= REQ_NOMERGE;
-}
-
-/*
* add arq to rbtree and fifo
*/
static void as_add_request(request_queue_t *q, struct request *rq)
{
struct as_data *ad = q->elevator->elevator_data;
struct as_rq *arq = RQ_DATA(rq);
- struct as_rq *alias;
int data_dir;
if (arq->state != AS_RQ_PRESCHED) {
@@ -1393,33 +1352,17 @@ static void as_add_request(request_queue
atomic_inc(&arq->io_context->aic->nr_queued);
}
- alias = as_add_arq_rb(ad, arq);
- if (!alias) {
- /*
- * set expire time (only used for reads) and add to fifo list
- */
- arq->expires = jiffies + ad->fifo_expire[data_dir];
- list_add_tail(&arq->fifo, &ad->fifo_list[data_dir]);
+ as_add_arq_rb(ad, arq);
+ if (rq_mergeable(arq->request))
+ as_add_arq_hash(ad, arq);
- if (rq_mergeable(arq->request))
- as_add_arq_hash(ad, arq);
- as_update_arq(ad, arq); /* keep state machine up to date */
-
- } else {
- as_add_aliased_request(ad, arq, alias);
-
- /*
- * have we been anticipating this request?
- * or does it come from the same process as the one we are
- * anticipating for?
- */
- if (ad->antic_status == ANTIC_WAIT_REQ
- || ad->antic_status == ANTIC_WAIT_NEXT) {
- if (as_can_break_anticipation(ad, arq))
- as_antic_stop(ad);
- }
- }
+ /*
+ * set expire time (only used for reads) and add to fifo list
+ */
+ arq->expires = jiffies + ad->fifo_expire[data_dir];
+ list_add_tail(&arq->fifo, &ad->fifo_list[data_dir]);
+ as_update_arq(ad, arq); /* keep state machine up to date */
arq->state = AS_RQ_QUEUED;
}
@@ -1542,23 +1485,8 @@ static void as_merged_request(request_qu
* if the merge was a front merge, we need to reposition request
*/
if (rq_rb_key(req) != arq->rb_key) {
- struct as_rq *alias, *next_arq = NULL;
-
- if (ad->next_arq[arq->is_sync] == arq)
- next_arq = as_find_next_arq(ad, arq);
-
- /*
- * Note! We should really be moving any old aliased requests
- * off this request and try to insert them into the rbtree. We
- * currently don't bother. Ditto the next function.
- */
as_del_arq_rb(ad, arq);
- if ((alias = as_add_arq_rb(ad, arq))) {
- list_del_init(&arq->fifo);
- as_add_aliased_request(ad, arq, alias);
- if (next_arq)
- ad->next_arq[arq->is_sync] = next_arq;
- }
+ as_add_arq_rb(ad, arq);
/*
* Note! At this stage of this and the next function, our next
* request may not be optimal - eg the request may have "grown"
@@ -1585,18 +1513,8 @@ static void as_merged_requests(request_q
as_add_arq_hash(ad, arq);
if (rq_rb_key(req) != arq->rb_key) {
- struct as_rq *alias, *next_arq = NULL;
-
- if (ad->next_arq[arq->is_sync] == arq)
- next_arq = as_find_next_arq(ad, arq);
-
as_del_arq_rb(ad, arq);
- if ((alias = as_add_arq_rb(ad, arq))) {
- list_del_init(&arq->fifo);
- as_add_aliased_request(ad, arq, alias);
- if (next_arq)
- ad->next_arq[arq->is_sync] = next_arq;
- }
+ as_add_arq_rb(ad, arq);
}
/*
@@ -1616,18 +1534,6 @@ static void as_merged_requests(request_q
}
/*
- * Transfer list of aliases
- */
- while (!list_empty(&next->queuelist)) {
- struct request *__rq = list_entry_rq(next->queuelist.next);
- struct as_rq *__arq = RQ_DATA(__rq);
-
- list_move_tail(&__rq->queuelist, &req->queuelist);
-
- WARN_ON(__arq->state != AS_RQ_QUEUED);
- }
-
- /*
* kill knowledge of next, this one is a goner
*/
as_remove_queued_request(q, next);
-
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