Re: [PATCH linux-2.6-block:master 01/05] blk: implement generic dispatch queue

From: Tejun Heo
Date: Tue Jul 26 2005 - 08:59:35 EST

01_blk_implement-generic-dispatch-queue.patch

Implements generic dispatch queue which can replace all
dispatch queues implemented by each iosched. This reduces
code duplication, eases enforcing semantics over dispatch
queue, and simplifies specific ioscheds.

Signed-off-by: Tejun Heo <htejun@xxxxxxxxx>

drivers/block/elevator.c | 242 ++++++++++++++++++++++++++++++++--------------
drivers/block/ll_rw_blk.c | 23 ++--
include/linux/blkdev.h | 17 ++-
include/linux/elevator.h | 16 +--
4 files changed, 201 insertions(+), 97 deletions(-)

Index: blk-fixes/drivers/block/elevator.c
===================================================================
--- blk-fixes.orig/drivers/block/elevator.c 2005-07-26 22:55:00.000000000 +0900
+++ blk-fixes/drivers/block/elevator.c 2005-07-26 22:55:00.000000000 +0900
@@ -40,6 +40,11 @@
static DEFINE_SPINLOCK(elv_list_lock);
static LIST_HEAD(elv_list);

+static inline sector_t rq_last_sector(struct request *rq)
+{
+ return rq->sector + rq->nr_sectors;
+}
+
/*
* can we safely merge with this request?
*/
@@ -143,6 +148,9 @@ static int elevator_attach(request_queue
INIT_LIST_HEAD(&q->queue_head);
q->last_merge = NULL;
q->elevator = eq;
+ q->last_sector = 0;
+ q->boundary_rq = NULL;
+ q->max_back_kb = 0;

if (eq->ops->elevator_init_fn)
ret = eq->ops->elevator_init_fn(q, eq);
@@ -225,6 +233,48 @@ void elevator_exit(elevator_t *e)
kfree(e);
}

+/*
+ * Insert rq into dispatch queue of q. Queue lock must be held on
+ * entry. If sort != 0, rq is sort-inserted; otherwise, rq will be
+ * appended to the dispatch queue. To be used by specific elevators.
+ */
+void elv_dispatch_insert(request_queue_t *q, struct request *rq, int sort)
+{
+ sector_t boundary;
+ unsigned max_back;
+ struct list_head *entry;
+
+ if (!sort) {
+ /* Specific elevator is performing sort. Step away. */
+ q->last_sector = rq_last_sector(rq);
+ q->boundary_rq = rq;
+ list_add_tail(&rq->queuelist, &q->queue_head);
+ return;
+ }
+
+ boundary = q->last_sector;
+ max_back = q->max_back_kb * 2;
+ boundary = boundary > max_back ? boundary - max_back : 0;
+
+ list_for_each_prev(entry, &q->queue_head) {
+ struct request *pos = list_entry_rq(entry);
+
+ if (pos->flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
+ break;
+ if (rq->sector >= boundary) {
+ if (pos->sector < boundary)
+ continue;
+ } else {
+ if (pos->sector >= boundary)
+ break;
+ }
+ if (rq->sector >= pos->sector)
+ break;
+ }
+
+ list_add(&rq->queuelist, entry);
+}
+
int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
{
elevator_t *e = q->elevator;
@@ -255,13 +305,7 @@ void elv_merge_requests(request_queue_t
e->ops->elevator_merge_req_fn(q, rq, next);
}

-/*
- * For careful internal use by the block layer. Essentially the same as
- * a requeue in that it tells the io scheduler that this request is not
- * active in the driver or hardware anymore, but we don't want the request
- * added back to the scheduler. Function is not exported.
- */
-void elv_deactivate_request(request_queue_t *q, struct request *rq)
+void elv_requeue_request(request_queue_t *q, struct request *rq)
{
elevator_t *e = q->elevator;

@@ -269,19 +313,14 @@ void elv_deactivate_request(request_queu
* it already went through dequeue, we need to decrement the
* in_flight count again
*/
- if (blk_account_rq(rq))
+ if (blk_account_rq(rq)) {
q->in_flight--;
+ if (blk_sorted_rq(rq) && e->ops->elevator_deactivate_req_fn)
+ e->ops->elevator_deactivate_req_fn(q, rq);
+ }

rq->flags &= ~REQ_STARTED;

- if (e->ops->elevator_deactivate_req_fn)
- e->ops->elevator_deactivate_req_fn(q, rq);
-}
-
-void elv_requeue_request(request_queue_t *q, struct request *rq)
-{
- elv_deactivate_request(q, rq);
-
/*
* if this is the flush, requeue the original instead and drop the flush
*/
@@ -290,55 +329,89 @@ void elv_requeue_request(request_queue_t
rq = rq->end_io_data;
}

- /*
- * the request is prepped and may have some resources allocated.
- * allowing unprepped requests to pass this one may cause resource
- * deadlock. turn on softbarrier.
- */
- rq->flags |= REQ_SOFTBARRIER;
-
- /*
- * if iosched has an explicit requeue hook, then use that. otherwise
- * just put the request at the front of the queue
- */
- if (q->elevator->ops->elevator_requeue_req_fn)
- q->elevator->ops->elevator_requeue_req_fn(q, rq);
- else
- __elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
+ __elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
}

void __elv_add_request(request_queue_t *q, struct request *rq, int where,
int plug)
{
- /*
- * barriers implicitly indicate back insertion
- */
- if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER) &&
- where == ELEVATOR_INSERT_SORT)
- where = ELEVATOR_INSERT_BACK;
+ if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
+ /*
+ * barriers implicitly indicate back insertion
+ */
+ if (where == ELEVATOR_INSERT_SORT)
+ where = ELEVATOR_INSERT_BACK;
+
+ /*
+ * this request is scheduling boundary, update last_sector
+ */
+ if (blk_fs_request(rq)) {
+ q->last_sector = rq_last_sector(rq);
+ q->boundary_rq = rq;
+ }
+ }

if (plug)
blk_plug_device(q);

rq->q = q;

- if (!test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags)) {
- q->elevator->ops->elevator_add_req_fn(q, rq, where);
-
- if (blk_queue_plugged(q)) {
- int nrq = q->rq.count[READ] + q->rq.count[WRITE]
- - q->in_flight;
-
- if (nrq >= q->unplug_thresh)
- __generic_unplug_device(q);
- }
- } else
+ if (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags))) {
/*
* if drain is set, store the request "locally". when the drain
* is finished, the requests will be handed ordered to the io
* scheduler
*/
list_add_tail(&rq->queuelist, &q->drain_list);
+ return;
+ }
+
+ switch (where) {
+ case ELEVATOR_INSERT_FRONT:
+ rq->flags |= REQ_SOFTBARRIER;
+
+ list_add(&rq->queuelist, &q->queue_head);
+ break;
+
+ case ELEVATOR_INSERT_BACK:
+ rq->flags |= REQ_SOFTBARRIER;
+
+ while (q->elevator->ops->elevator_dispatch_fn(q, 1))
+ ;
+ list_add_tail(&rq->queuelist, &q->queue_head);
+ /*
+ * We kick the queue here for the following reasons.
+ * - The elevator might have returned NULL previously
+ * to delay requests and returned them now. As the
+ * queue wasn't empty before this request, ll_rw_blk
+ * won't run the queue on return, resulting in hang.
+ * - Usually, back inserted requests won't be merged
+ * with anything. There's no point in delaying queue
+ * processing.
+ */
+ blk_remove_plug(q);
+ q->request_fn(q);
+ break;
+
+ case ELEVATOR_INSERT_SORT:
+ BUG_ON(!blk_fs_request(rq));
+ rq->flags |= REQ_SORTED;
+ q->elevator->ops->elevator_add_req_fn(q, rq);
+ break;
+
+ default:
+ printk(KERN_ERR "%s: bad insertion point %d\n",
+ __FUNCTION__, where);
+ BUG();
+ }
+
+ if (blk_queue_plugged(q)) {
+ int nrq = q->rq.count[READ] + q->rq.count[WRITE]
+ - q->in_flight;
+
+ if (nrq >= q->unplug_thresh)
+ __generic_unplug_device(q);
+ }
}

void elv_add_request(request_queue_t *q, struct request *rq, int where,
@@ -353,13 +426,19 @@ void elv_add_request(request_queue_t *q,

static inline struct request *__elv_next_request(request_queue_t *q)
{
- struct request *rq = q->elevator->ops->elevator_next_req_fn(q);
+ struct request *rq;
+
+ if (unlikely(list_empty(&q->queue_head) &&
+ !q->elevator->ops->elevator_dispatch_fn(q, 0)))
+ return NULL;
+
+ rq = list_entry_rq(q->queue_head.next);

/*
* if this is a barrier write and the device has to issue a
* flush sequence to support it, check how far we are
*/
- if (rq && blk_fs_request(rq) && blk_barrier_rq(rq)) {
+ if (blk_fs_request(rq) && blk_barrier_rq(rq)) {
BUG_ON(q->ordered == QUEUE_ORDERED_NONE);

if (q->ordered == QUEUE_ORDERED_FLUSH &&
@@ -376,16 +455,34 @@ struct request *elv_next_request(request
int ret;

while ((rq = __elv_next_request(q)) != NULL) {
- /*
- * just mark as started even if we don't start it, a request
- * that has been delayed should not be passed by new incoming
- * requests
- */
- rq->flags |= REQ_STARTED;
+ if (!(rq->flags & REQ_STARTED)) {
+ elevator_t *e = q->elevator;
+
+ /*
+ * This is the first time the device driver
+ * sees this request (possibly after
+ * requeueing). Notify IO scheduler.
+ */
+ if (blk_sorted_rq(rq) &&
+ e->ops->elevator_activate_req_fn)
+ e->ops->elevator_activate_req_fn(q, rq);
+
+ /*
+ * just mark as started even if we don't start
+ * it, a request that has been delayed should
+ * not be passed by new incoming requests
+ */
+ rq->flags |= REQ_STARTED;
+ }

if (rq == q->last_merge)
q->last_merge = NULL;

+ if (!q->boundary_rq || q->boundary_rq == rq) {
+ q->last_sector = rq_last_sector(rq);
+ q->boundary_rq = NULL;
+ }
+
if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
break;

@@ -396,9 +493,9 @@ struct request *elv_next_request(request
/*
* the request may have been (partially) prepped.
* we need to keep this request in the front to
- * avoid resource deadlock. turn on softbarrier.
+ * avoid resource deadlock. REQ_STARTED will
+ * prevent other fs requests from passing this one.
*/
- rq->flags |= REQ_SOFTBARRIER;
rq = NULL;
break;
} else if (ret == BLKPREP_KILL) {
@@ -421,16 +518,16 @@ struct request *elv_next_request(request
return rq;
}

-void elv_remove_request(request_queue_t *q, struct request *rq)
+void elv_dequeue_request(request_queue_t *q, struct request *rq)
{
- elevator_t *e = q->elevator;
+ BUG_ON(list_empty(&rq->queuelist));
+
+ list_del_init(&rq->queuelist);

/*
* the time frame between a request being removed from the lists
* and to it is freed is accounted as io that is in progress at
- * the driver side. note that we only account requests that the
- * driver has seen (REQ_STARTED set), to avoid false accounting
- * for request-request merges
+ * the driver side.
*/
if (blk_account_rq(rq))
q->in_flight++;
@@ -444,19 +541,19 @@ void elv_remove_request(request_queue_t
*/
if (rq == q->last_merge)
q->last_merge = NULL;
-
- if (e->ops->elevator_remove_req_fn)
- e->ops->elevator_remove_req_fn(q, rq);
}

int elv_queue_empty(request_queue_t *q)
{
elevator_t *e = q->elevator;

+ if (!list_empty(&q->queue_head))
+ return 0;
+
if (e->ops->elevator_queue_empty_fn)
return e->ops->elevator_queue_empty_fn(q);

- return list_empty(&q->queue_head);
+ return 1;
}

struct request *elv_latter_request(request_queue_t *q, struct request *rq)
@@ -527,11 +624,11 @@ void elv_completed_request(request_queue
/*
* request is released from the driver, io must be done
*/
- if (blk_account_rq(rq))
+ if (blk_account_rq(rq)) {
q->in_flight--;
-
- if (e->ops->elevator_completed_req_fn)
- e->ops->elevator_completed_req_fn(q, rq);
+ if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
+ e->ops->elevator_completed_req_fn(q, rq);
+ }
}

int elv_register_queue(struct request_queue *q)
@@ -704,11 +801,12 @@ ssize_t elv_iosched_show(request_queue_t
return len;
}

+EXPORT_SYMBOL(elv_dispatch_insert);
EXPORT_SYMBOL(elv_add_request);
EXPORT_SYMBOL(__elv_add_request);
EXPORT_SYMBOL(elv_requeue_request);
EXPORT_SYMBOL(elv_next_request);
-EXPORT_SYMBOL(elv_remove_request);
+EXPORT_SYMBOL(elv_dequeue_request);
EXPORT_SYMBOL(elv_queue_empty);
EXPORT_SYMBOL(elv_completed_request);
EXPORT_SYMBOL(elevator_exit);
Index: blk-fixes/drivers/block/ll_rw_blk.c
===================================================================
--- blk-fixes.orig/drivers/block/ll_rw_blk.c 2005-07-26 22:54:59.000000000 +0900
+++ blk-fixes/drivers/block/ll_rw_blk.c 2005-07-26 22:55:00.000000000 +0900
@@ -349,6 +349,8 @@ static void blk_pre_flush_end_io(struct
struct request *rq = flush_rq->end_io_data;
request_queue_t *q = rq->q;

+ elv_completed_request(q, flush_rq);
+
rq->flags |= REQ_BAR_PREFLUSH;

if (!flush_rq->errors)
@@ -365,6 +367,8 @@ static void blk_post_flush_end_io(struct
struct request *rq = flush_rq->end_io_data;
request_queue_t *q = rq->q;

+ elv_completed_request(q, flush_rq);
+
rq->flags |= REQ_BAR_POSTFLUSH;

q->end_flush_fn(q, flush_rq);
@@ -404,8 +408,6 @@ struct request *blk_start_pre_flush(requ
if (!list_empty(&rq->queuelist))
blkdev_dequeue_request(rq);

- elv_deactivate_request(q, rq);
-
flush_rq->end_io_data = rq;
flush_rq->end_io = blk_pre_flush_end_io;

@@ -1036,6 +1038,7 @@ EXPORT_SYMBOL(blk_queue_invalidate_tags)
static char *rq_flags[] = {
"REQ_RW",
"REQ_FAILFAST",
+ "REQ_SORTED",
"REQ_SOFTBARRIER",
"REQ_HARDBARRIER",
"REQ_CMD",
@@ -2370,6 +2373,8 @@ static void __blk_put_request(request_qu
if (unlikely(--req->ref_count))
return;

+ elv_completed_request(q, req);
+
req->rq_status = RQ_INACTIVE;
req->q = NULL;
req->rl = NULL;
@@ -2381,8 +2386,6 @@ static void __blk_put_request(request_qu
if (rl) {
int rw = rq_data_dir(req);

- elv_completed_request(q, req);
-
BUG_ON(!list_empty(&req->queuelist));

blk_free_request(q, req);
@@ -2392,14 +2395,14 @@ static void __blk_put_request(request_qu

void blk_put_request(struct request *req)
{
+ unsigned long flags;
+ request_queue_t *q = req->q;
+
/*
- * if req->rl isn't set, this request didnt originate from the
- * block layer, so it's safe to just disregard it
+ * Gee, IDE calls in w/ NULL q. Fix IDE and remove the
+ * following if (q) test.
*/
- if (req->rl) {
- unsigned long flags;
- request_queue_t *q = req->q;
-
+ if (q) {
spin_lock_irqsave(q->queue_lock, flags);
__blk_put_request(q, req);
spin_unlock_irqrestore(q->queue_lock, flags);
Index: blk-fixes/include/linux/blkdev.h
===================================================================
--- blk-fixes.orig/include/linux/blkdev.h 2005-07-26 22:54:59.000000000 +0900
+++ blk-fixes/include/linux/blkdev.h 2005-07-26 22:55:00.000000000 +0900
@@ -193,6 +193,7 @@ struct request {
enum rq_flag_bits {
__REQ_RW, /* not set, read. set, write */
__REQ_FAILFAST, /* no low level driver retries */
+ __REQ_SORTED, /* elevator knows about this request */
__REQ_SOFTBARRIER, /* may not be passed by ioscheduler */
__REQ_HARDBARRIER, /* may not be passed by drive either */
__REQ_CMD, /* is a regular fs rw request */
@@ -225,6 +226,7 @@ enum rq_flag_bits {

#define REQ_RW (1 << __REQ_RW)
#define REQ_FAILFAST (1 << __REQ_FAILFAST)
+#define REQ_SORTED (1 << __REQ_SORTED)
#define REQ_SOFTBARRIER (1 << __REQ_SOFTBARRIER)
#define REQ_HARDBARRIER (1 << __REQ_HARDBARRIER)
#define REQ_CMD (1 << __REQ_CMD)
@@ -326,6 +328,13 @@ struct request_queue
end_flush_fn *end_flush_fn;

/*
+ * Dispatch queue sorting
+ */
+ sector_t last_sector;
+ struct request *boundary_rq;
+ unsigned int max_back_kb;
+
+ /*
* Auto-unplugging state
*/
struct timer_list unplug_timer;
@@ -446,6 +455,7 @@ enum {
#define blk_pm_request(rq) \
((rq)->flags & (REQ_PM_SUSPEND | REQ_PM_RESUME))

+#define blk_sorted_rq(rq) ((rq)->flags & REQ_SORTED)
#define blk_barrier_rq(rq) ((rq)->flags & REQ_HARDBARRIER)
#define blk_barrier_preflush(rq) ((rq)->flags & REQ_BAR_PREFLUSH)
#define blk_barrier_postflush(rq) ((rq)->flags & REQ_BAR_POSTFLUSH)
@@ -604,12 +614,7 @@ extern void end_request(struct request *

static inline void blkdev_dequeue_request(struct request *req)
{
- BUG_ON(list_empty(&req->queuelist));
-
- list_del_init(&req->queuelist);
-
- if (req->rl)
- elv_remove_request(req->q, req);
+ elv_dequeue_request(req->q, req);
}

/*
Index: blk-fixes/include/linux/elevator.h
===================================================================
--- blk-fixes.orig/include/linux/elevator.h 2005-07-26 22:54:59.000000000 +0900
+++ blk-fixes/include/linux/elevator.h 2005-07-26 22:55:00.000000000 +0900
@@ -8,18 +8,17 @@ typedef void (elevator_merge_req_fn) (re

typedef void (elevator_merged_fn) (request_queue_t *, struct request *);

-typedef struct request *(elevator_next_req_fn) (request_queue_t *);
+typedef int (elevator_dispatch_fn) (request_queue_t *, int);

-typedef void (elevator_add_req_fn) (request_queue_t *, struct request *, int);
+typedef void (elevator_add_req_fn) (request_queue_t *, struct request *);
typedef int (elevator_queue_empty_fn) (request_queue_t *);
-typedef void (elevator_remove_req_fn) (request_queue_t *, struct request *);
-typedef void (elevator_requeue_req_fn) (request_queue_t *, struct request *);
typedef struct request *(elevator_request_list_fn) (request_queue_t *, struct request *);
typedef void (elevator_completed_req_fn) (request_queue_t *, struct request *);
typedef int (elevator_may_queue_fn) (request_queue_t *, int);

typedef int (elevator_set_req_fn) (request_queue_t *, struct request *, int);
typedef void (elevator_put_req_fn) (request_queue_t *, struct request *);
+typedef void (elevator_activate_req_fn) (request_queue_t *, struct request *);
typedef void (elevator_deactivate_req_fn) (request_queue_t *, struct request *);

typedef int (elevator_init_fn) (request_queue_t *, elevator_t *);
@@ -31,10 +30,9 @@ struct elevator_ops
elevator_merged_fn *elevator_merged_fn;
elevator_merge_req_fn *elevator_merge_req_fn;

- elevator_next_req_fn *elevator_next_req_fn;
+ elevator_dispatch_fn *elevator_dispatch_fn;
elevator_add_req_fn *elevator_add_req_fn;
- elevator_remove_req_fn *elevator_remove_req_fn;
- elevator_requeue_req_fn *elevator_requeue_req_fn;
+ elevator_activate_req_fn *elevator_activate_req_fn;
elevator_deactivate_req_fn *elevator_deactivate_req_fn;

elevator_queue_empty_fn *elevator_queue_empty_fn;
@@ -81,15 +79,15 @@ struct elevator_queue
/*
* block elevator interface
*/
+extern void elv_dispatch_insert(request_queue_t *, struct request *, int);
extern void elv_add_request(request_queue_t *, struct request *, int, int);
extern void __elv_add_request(request_queue_t *, struct request *, int, int);
extern int elv_merge(request_queue_t *, struct request **, struct bio *);
extern void elv_merge_requests(request_queue_t *, struct request *,
struct request *);
extern void elv_merged_request(request_queue_t *, struct request *);
-extern void elv_remove_request(request_queue_t *, struct request *);
+extern void elv_dequeue_request(request_queue_t *, struct request *);
extern void elv_requeue_request(request_queue_t *, struct request *);
-extern void elv_deactivate_request(request_queue_t *, struct request *);
extern int elv_queue_empty(request_queue_t *);
extern struct request *elv_next_request(struct request_queue *q);
extern struct request *elv_former_request(request_queue_t *, struct request *);

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