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SubjectRe: [PATCH 5/15] cfq-iosched: speed up rbtree handling
On Wed, Apr 25 2007, Jens Axboe wrote:
> On Wed, Apr 25 2007, Alan D. Brunelle wrote:
> > Hi Jens -
> >
> > The attached patch speeds it up even more - I'm finding a >9% reduction
> > in %system with no loss in IO performance. This just sets the cached
> > element when the first is looked for.
>
> Interesting, good thinking. It should not change the IO pattern, as the
> end result should be the same. Thanks Alan, will commit!
>
> I'll give elevator.c the same treatment, should be even more beneficial.
> Stay tuned for a test patch.

Something like this, totally untested (it compiles). I initially wanted
to fold the cfq addon into the elevator.h provided implementation, but
that requires more extensive changes. Given how little code it is, I
think I'll keep them seperate.

diff --git a/block/as-iosched.c b/block/as-iosched.c
index ef12627..37c6fb3 100644
--- a/block/as-iosched.c
+++ b/block/as-iosched.c
@@ -89,7 +89,7 @@ struct as_data {
/*
* requests (as_rq s) are present on both sort_list and fifo_list
*/
- struct rb_root sort_list[2];
+ struct blk_rb_root sort_list[2];
struct list_head fifo_list[2];

struct request *next_rq[2]; /* next in sort order */
@@ -369,9 +369,9 @@ as_find_next_rq(struct as_data *ad, struct request *last)
else {
const int data_dir = rq_is_sync(last);

- rbnext = rb_first(&ad->sort_list[data_dir]);
- if (rbnext && rbnext != &last->rb_node)
- next = rb_entry_rq(rbnext);
+ next = elv_rb_first(&ad->sort_list[data_dir]);
+ if (next == last)
+ next = NULL;
}

return as_choose_req(ad, next, prev);
@@ -1057,7 +1057,7 @@ static int as_dispatch_request(request_queue_t *q, int force)
*/

if (reads) {
- BUG_ON(RB_EMPTY_ROOT(&ad->sort_list[REQ_SYNC]));
+ BUG_ON(BLK_RB_EMPTY_ROOT(&ad->sort_list[REQ_SYNC]));

if (writes && ad->batch_data_dir == REQ_SYNC)
/*
@@ -1081,7 +1081,7 @@ static int as_dispatch_request(request_queue_t *q, int force)

if (writes) {
dispatch_writes:
- BUG_ON(RB_EMPTY_ROOT(&ad->sort_list[REQ_ASYNC]));
+ BUG_ON(BLK_RB_EMPTY_ROOT(&ad->sort_list[REQ_ASYNC]));

if (ad->batch_data_dir == REQ_SYNC) {
ad->changed_batch = 1;
@@ -1337,8 +1337,8 @@ static void *as_init_queue(request_queue_t *q)

INIT_LIST_HEAD(&ad->fifo_list[REQ_SYNC]);
INIT_LIST_HEAD(&ad->fifo_list[REQ_ASYNC]);
- ad->sort_list[REQ_SYNC] = RB_ROOT;
- ad->sort_list[REQ_ASYNC] = RB_ROOT;
+ ad->sort_list[REQ_SYNC] = BLK_RB_ROOT;
+ ad->sort_list[REQ_ASYNC] = BLK_RB_ROOT;
ad->fifo_expire[REQ_SYNC] = default_read_expire;
ad->fifo_expire[REQ_ASYNC] = default_write_expire;
ad->antic_expire = default_antic_expire;
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 7a18f31..f3020aa 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -127,7 +127,7 @@ struct cfq_queue {
/* service_tree key */
unsigned long rb_key;
/* sorted list of pending requests */
- struct rb_root sort_list;
+ struct blk_rb_root sort_list;
/* if fifo isn't expired, next request to serve */
struct request *next_rq;
/* requests queued in sort_list */
@@ -419,9 +419,9 @@ cfq_find_next_rq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
if (rbnext)
next = rb_entry_rq(rbnext);
else {
- rbnext = rb_first(&cfqq->sort_list);
- if (rbnext && rbnext != &last->rb_node)
- next = rb_entry_rq(rbnext);
+ next = elv_rb_first(&cfqq->sort_list);
+ if (next == last)
+ next = NULL;
}

return cfq_choose_req(cfqd, next, prev);
@@ -564,7 +564,7 @@ static inline void cfq_del_rq_rb(struct request *rq)

elv_rb_del(&cfqq->sort_list, rq);

- if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list))
+ if (cfq_cfqq_on_rr(cfqq) && BLK_RB_EMPTY_ROOT(&cfqq->sort_list))
cfq_del_cfqq_rr(cfqd, cfqq);
}

@@ -871,7 +871,7 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd)
struct cfq_io_context *cic;
unsigned long sl;

- WARN_ON(!RB_EMPTY_ROOT(&cfqq->sort_list));
+ WARN_ON(!BLK_RB_EMPTY_ROOT(&cfqq->sort_list));
WARN_ON(cfq_cfqq_slice_new(cfqq));

/*
@@ -983,7 +983,7 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
* The active queue has requests and isn't expired, allow it to
* dispatch.
*/
- if (!RB_EMPTY_ROOT(&cfqq->sort_list))
+ if (!BLK_RB_EMPTY_ROOT(&cfqq->sort_list))
goto keep_queue;

/*
@@ -1015,7 +1015,7 @@ __cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq,
{
int dispatched = 0;

- BUG_ON(RB_EMPTY_ROOT(&cfqq->sort_list));
+ BUG_ON(BLK_RB_EMPTY_ROOT(&cfqq->sort_list));

do {
struct request *rq;
@@ -1038,7 +1038,7 @@ __cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq,
cfqd->active_cic = RQ_CIC(rq);
}

- if (RB_EMPTY_ROOT(&cfqq->sort_list))
+ if (BLK_RB_EMPTY_ROOT(&cfqq->sort_list))
break;

} while (dispatched < max_dispatch);
@@ -1147,7 +1147,7 @@ static void cfq_put_queue(struct cfq_queue *cfqq)
if (!atomic_dec_and_test(&cfqq->ref))
return;

- BUG_ON(rb_first(&cfqq->sort_list));
+ BUG_ON(elv_rb_first(&cfqq->sort_list));
BUG_ON(cfqq->allocated[READ] + cfqq->allocated[WRITE]);
BUG_ON(cfq_cfqq_on_rr(cfqq));

@@ -1385,6 +1385,7 @@ retry:

memset(cfqq, 0, sizeof(*cfqq));

+ cfqq->sort_list = BLK_RB_ROOT;
RB_CLEAR_NODE(&cfqq->rb_node);
INIT_LIST_HEAD(&cfqq->fifo);

@@ -1783,7 +1784,7 @@ static void cfq_completed_request(request_queue_t *q, struct request *rq)
}
if (cfq_slice_used(cfqq))
cfq_slice_expired(cfqd, 1);
- else if (sync && RB_EMPTY_ROOT(&cfqq->sort_list))
+ else if (sync && BLK_RB_EMPTY_ROOT(&cfqq->sort_list))
cfq_arm_slice_timer(cfqd);
}

@@ -1973,7 +1974,7 @@ static void cfq_idle_slice_timer(unsigned long data)
/*
* not expired and it has a request pending, let it dispatch
*/
- if (!RB_EMPTY_ROOT(&cfqq->sort_list)) {
+ if (!BLK_RB_EMPTY_ROOT(&cfqq->sort_list)) {
cfq_mark_cfqq_must_dispatch(cfqq);
goto out_kick;
}
diff --git a/block/deadline-iosched.c b/block/deadline-iosched.c
index 6d673e9..8db8709 100644
--- a/block/deadline-iosched.c
+++ b/block/deadline-iosched.c
@@ -31,7 +31,7 @@ struct deadline_data {
/*
* requests (deadline_rq s) are present on both sort_list and fifo_list
*/
- struct rb_root sort_list[2];
+ struct blk_rb_root sort_list[2];
struct list_head fifo_list[2];

/*
@@ -58,11 +58,10 @@ static void deadline_move_request(struct deadline_data *, struct request *);
static void
deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
{
- struct rb_root *root = RQ_RB_ROOT(dd, rq);
struct request *__alias;

retry:
- __alias = elv_rb_add(root, rq);
+ __alias = elv_rb_add(RQ_RB_ROOT(dd, rq), rq);
if (unlikely(__alias)) {
deadline_move_request(dd, __alias);
goto retry;
@@ -270,7 +269,7 @@ static int deadline_dispatch_requests(request_queue_t *q, int force)
*/

if (reads) {
- BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));
+ BUG_ON(BLK_RB_EMPTY_ROOT(&dd->sort_list[READ]));

if (writes && (dd->starved++ >= dd->writes_starved))
goto dispatch_writes;
@@ -286,7 +285,7 @@ static int deadline_dispatch_requests(request_queue_t *q, int force)

if (writes) {
dispatch_writes:
- BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
+ BUG_ON(BLK_RB_EMPTY_ROOT(&dd->sort_list[WRITE]));

dd->starved = 0;

@@ -313,16 +312,13 @@ dispatch_find_request:
*/
rq = dd->next_rq[data_dir];
} else {
- struct rb_node *node;
/*
* The last req was the other direction or we have run out of
* higher-sectored requests. Go back to the lowest sectored
* request (1 way elevator) and start a new batch.
*/
dd->batching = 0;
- node = rb_first(&dd->sort_list[data_dir]);
- if (node)
- rq = rb_entry_rq(node);
+ rq = elv_rb_first(&dd->sort_list[data_dir]);
}

dispatch_request:
@@ -367,8 +363,8 @@ static void *deadline_init_queue(request_queue_t *q)

INIT_LIST_HEAD(&dd->fifo_list[READ]);
INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
- dd->sort_list[READ] = RB_ROOT;
- dd->sort_list[WRITE] = RB_ROOT;
+ dd->sort_list[READ] = BLK_RB_ROOT;
+ dd->sort_list[WRITE] = BLK_RB_ROOT;
dd->fifo_expire[READ] = read_expire;
dd->fifo_expire[WRITE] = write_expire;
dd->writes_starved = writes_starved;
diff --git a/block/elevator.c b/block/elevator.c
index 96a00c8..8f1c287 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -336,11 +336,12 @@ static struct request *elv_rqhash_find(request_queue_t *q, sector_t offset)
* RB-tree support functions for inserting/lookup/removal of requests
* in a sorted RB tree.
*/
-struct request *elv_rb_add(struct rb_root *root, struct request *rq)
+struct request *elv_rb_add(struct blk_rb_root *root, struct request *rq)
{
- struct rb_node **p = &root->rb_node;
+ struct rb_node **p = &root->tree.rb_node;
struct rb_node *parent = NULL;
struct request *__rq;
+ int left = 1;

while (*p) {
parent = *p;
@@ -348,31 +349,38 @@ struct request *elv_rb_add(struct rb_root *root, struct request *rq)

if (rq->sector < __rq->sector)
p = &(*p)->rb_left;
- else if (rq->sector > __rq->sector)
+ else if (rq->sector > __rq->sector) {
p = &(*p)->rb_right;
- else
+ left = 0;
+ } else
return __rq;
}

+ if (left)
+ root->left = &rq->rb_node;
+
rb_link_node(&rq->rb_node, parent, p);
- rb_insert_color(&rq->rb_node, root);
+ rb_insert_color(&rq->rb_node, &root->tree);
return NULL;
}

EXPORT_SYMBOL(elv_rb_add);

-void elv_rb_del(struct rb_root *root, struct request *rq)
+void elv_rb_del(struct blk_rb_root *root, struct request *rq)
{
+ if (root->left == &rq->rb_node)
+ root->left = NULL;
+
BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
- rb_erase(&rq->rb_node, root);
+ rb_erase(&rq->rb_node, &root->tree);
RB_CLEAR_NODE(&rq->rb_node);
}

EXPORT_SYMBOL(elv_rb_del);

-struct request *elv_rb_find(struct rb_root *root, sector_t sector)
+struct request *elv_rb_find(struct blk_rb_root *root, sector_t sector)
{
- struct rb_node *n = root->rb_node;
+ struct rb_node *n = root->tree.rb_node;
struct request *rq;

while (n) {
@@ -391,6 +399,18 @@ struct request *elv_rb_find(struct rb_root *root, sector_t sector)

EXPORT_SYMBOL(elv_rb_find);

+struct request *elv_rb_first(struct blk_rb_root *root)
+{
+ if (!root->left)
+ root->left = rb_first(&root->tree);
+ if (root->left)
+ return rb_entry_rq(root->left);
+
+ return NULL;
+}
+
+EXPORT_SYMBOL(elv_rb_first);
+
/*
* Insert rq into dispatch queue of q. Queue lock must be held on
* entry. rq is sort insted into the dispatch queue. To be used by
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index e88fcbc..28cc010 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -139,11 +139,22 @@ extern struct request *elv_rb_former_request(request_queue_t *, struct request *
extern struct request *elv_rb_latter_request(request_queue_t *, struct request *);

/*
- * rb support functions.
+ * rb support functions below. we have a private rb_root setup where we
+ * cache the leftmost node in the tree, for fastest min element retrieval.
+ * this is the main purpose of the rbtree (sort and min extraction).
*/
-extern struct request *elv_rb_add(struct rb_root *, struct request *);
-extern void elv_rb_del(struct rb_root *, struct request *);
-extern struct request *elv_rb_find(struct rb_root *, sector_t);
+struct blk_rb_root {
+ struct rb_root tree;
+ struct rb_node *left;
+};
+
+#define BLK_RB_ROOT (struct blk_rb_root) { RB_ROOT, NULL, }
+#define BLK_RB_EMPTY_ROOT(root) RB_EMPTY_ROOT(&((root)->tree))
+
+extern struct request *elv_rb_add(struct blk_rb_root *, struct request *);
+extern void elv_rb_del(struct blk_rb_root *, struct request *);
+extern struct request *elv_rb_find(struct blk_rb_root *, sector_t);
+extern struct request *elv_rb_first(struct blk_rb_root *);

/*
* Return values from elevator merger
--
Jens Axboe

-
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