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cfq-iosched: development update 

- Implement logic for detecting cooperating processes, so we
  choose the best available queue whenever possible.

- Improve residual slice time accounting.

- Remove dead code: we no longer see async requests coming in on
  sync queues. That part was removed a long time ago. That means
  that we can also remove the difference between cfq_cfqq_sync()
  and cfq_cfqq_class_sync(), they are now indentical. And we can
  kill the on_dispatch array, just make it a counter.

- Allow a process to go into the current list, if it hasn't been
  serviced in this scheduler tick yet.

Possible future improvements including caching the cfqq lookup
in cfq_close_cooperator(), so we don't have to look it up twice.
cfq_get_best_queue() should just use that last decision instead
of doing it again.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2007-04-25 12:44:27 +02:00 committed by Jens Axboe
parent 1e3335de05
commit 6d048f5310
1 changed files with 262 additions and 121 deletions
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383
block/cfq-iosched.c
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@ -56,13 +56,7 @@ static struct completion *ioc_gone;
#define ASYNC (0)
#define SYNC (1)
#define cfq_cfqq_dispatched(cfqq) \
((cfqq)->on_dispatch[ASYNC] + (cfqq)->on_dispatch[SYNC])
#define cfq_cfqq_class_sync(cfqq) ((cfqq)->key != CFQ_KEY_ASYNC)
#define cfq_cfqq_sync(cfqq) \
(cfq_cfqq_class_sync(cfqq) || (cfqq)->on_dispatch[SYNC])
#define cfq_cfqq_sync(cfqq) ((cfqq)->key != CFQ_KEY_ASYNC)
#define sample_valid(samples) ((samples) > 80)
@ -79,6 +73,7 @@ struct cfq_data {
struct list_head busy_rr;
struct list_head cur_rr;
struct list_head idle_rr;
unsigned long cur_rr_tick;
unsigned int busy_queues;
/*
@ -98,11 +93,12 @@ struct cfq_data {
struct cfq_queue *active_queue;
struct cfq_io_context *active_cic;
int cur_prio, cur_end_prio;
unsigned long prio_time;
unsigned int dispatch_slice;
struct timer_list idle_class_timer;
sector_t last_sector;
sector_t last_position;
unsigned long last_end_request;
/*
@ -117,6 +113,9 @@ struct cfq_data {
unsigned int cfq_slice_idle;
struct list_head cic_list;
sector_t new_seek_mean;
u64 new_seek_total;
};
/*
@ -133,6 +132,8 @@ struct cfq_queue {
unsigned int key;
/* member of the rr/busy/cur/idle cfqd list */
struct list_head cfq_list;
/* in what tick we were last serviced */
unsigned long rr_tick;
/* sorted list of pending requests */
struct rb_root sort_list;
/* if fifo isn't expired, next request to serve */
@ -148,10 +149,11 @@ struct cfq_queue {
unsigned long slice_end;
unsigned long service_last;
unsigned long slice_start;
long slice_resid;
/* number of requests that are on the dispatch list */
int on_dispatch[2];
/* number of requests that are on the dispatch list or inside driver */
int dispatched;
/* io prio of this group */
unsigned short ioprio, org_ioprio;
@ -159,6 +161,8 @@ struct cfq_queue {
/* various state flags, see below */
unsigned int flags;
sector_t last_request_pos;
};
enum cfqq_state_flags {
@ -259,6 +263,8 @@ cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
* easily introduce oscillations.
*/
cfqq->slice_resid = 0;
cfqq->slice_start = jiffies;
}
/*
@ -307,7 +313,7 @@ cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2)
s1 = rq1->sector;
s2 = rq2->sector;
last = cfqd->last_sector;
last = cfqd->last_position;
/*
* by definition, 1KiB is 2 sectors
@ -398,39 +404,42 @@ cfq_find_next_rq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
return cfq_choose_req(cfqd, next, prev);
}
static void cfq_resort_rr_list(struct cfq_queue *cfqq, int preempted)
/*
* This function finds out where to insert a BE queue in the service hierarchy
*/
static void cfq_resort_be_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq,
int preempted)
{
struct cfq_data *cfqd = cfqq->cfqd;
struct list_head *list, *n;
struct cfq_queue *__cfqq;
int add_tail = 0;
/*
* Resorting requires the cfqq to be on the RR list already.
* if cfqq has requests in flight, don't allow it to be
* found in cfq_set_active_queue before it has finished them.
* this is done to increase fairness between a process that
* has lots of io pending vs one that only generates one
* sporadically or synchronously
*/
if (!cfq_cfqq_on_rr(cfqq))
return;
list_del(&cfqq->cfq_list);
if (cfq_class_rt(cfqq))
if (cfqq->dispatched)
list = &cfqd->busy_rr;
else if (cfqq->ioprio == (cfqd->cur_prio + 1) &&
cfq_cfqq_sync(cfqq) &&
(time_before(cfqd->prio_time, cfqq->service_last) ||
cfq_cfqq_queue_new(cfqq) || preempted)) {
list = &cfqd->cur_rr;
else if (cfq_class_idle(cfqq))
list = &cfqd->idle_rr;
else {
/*
* if cfqq has requests in flight, don't allow it to be
* found in cfq_set_active_queue before it has finished them.
* this is done to increase fairness between a process that
* has lots of io pending vs one that only generates one
* sporadically or synchronously
*/
if (cfq_cfqq_dispatched(cfqq))
list = &cfqd->busy_rr;
else
list = &cfqd->rr_list[cfqq->ioprio];
}
add_tail = 1;
} else
list = &cfqd->rr_list[cfqq->ioprio];
if (preempted || cfq_cfqq_queue_new(cfqq)) {
if (!cfq_cfqq_sync(cfqq) || add_tail) {
/*
* async queue always goes to the end. this wont be overly
* unfair to writes, as the sort of the sync queue wont be
* allowed to pass the async queue again.
*/
list_add_tail(&cfqq->cfq_list, list);
} else if (preempted || cfq_cfqq_queue_new(cfqq)) {
/*
* If this queue was preempted or is new (never been serviced),
* let it be added first for fairness but beind other new
@ -444,14 +453,7 @@ static void cfq_resort_rr_list(struct cfq_queue *cfqq, int preempted)
n = n->next;
}
list_add_tail(&cfqq->cfq_list, n);
} else if (!cfq_cfqq_class_sync(cfqq)) {
/*
* async queue always goes to the end. this wont be overly
* unfair to writes, as the sort of the sync queue wont be
* allowed to pass the async queue again.
*/
list_add_tail(&cfqq->cfq_list, list);
list_add(&cfqq->cfq_list, n);
} else {
/*
* sort by last service, but don't cross a new or async
@ -461,17 +463,54 @@ static void cfq_resort_rr_list(struct cfq_queue *cfqq, int preempted)
*/
n = list;
while ((n = n->prev) != list) {
struct cfq_queue *__cfqq = list_entry_cfqq(n);
struct cfq_queue *__c = list_entry_cfqq(n);
if (!cfq_cfqq_class_sync(cfqq) || !__cfqq->service_last)
if (!cfq_cfqq_sync(__c) || !__c->service_last)
break;
if (time_before(__cfqq->service_last, cfqq->service_last))
if (time_before(__c->service_last, cfqq->service_last))
break;
}
list_add(&cfqq->cfq_list, n);
}
}
static void cfq_resort_rr_list(struct cfq_queue *cfqq, int preempted)
{
struct cfq_data *cfqd = cfqq->cfqd;
struct list_head *n;
/*
* Resorting requires the cfqq to be on the RR list already.
*/
if (!cfq_cfqq_on_rr(cfqq))
return;
list_del(&cfqq->cfq_list);
if (cfq_class_rt(cfqq)) {
/*
* At to the front of the current list, but behind other
* RT queues.
*/
n = &cfqd->cur_rr;
while (n->next != &cfqd->cur_rr)
if (!cfq_class_rt(cfqq))
break;
list_add(&cfqq->cfq_list, n);
} else if (cfq_class_idle(cfqq)) {
/*
* IDLE goes to the tail of the idle list
*/
list_add_tail(&cfqq->cfq_list, &cfqd->idle_rr);
} else {
/*
* So we get here, ergo the queue is a regular best-effort queue
*/
cfq_resort_be_queue(cfqd, cfqq, preempted);
}
}
/*
* add to busy list of queues for service, trying to be fair in ordering
* the pending list according to last request service
@ -579,6 +618,8 @@ static void cfq_activate_request(request_queue_t *q, struct request *rq)
*/
if (!cfqd->hw_tag && cfqd->rq_in_driver > 4)
cfqd->hw_tag = 1;
cfqd->last_position = rq->hard_sector + rq->hard_nr_sectors;
}
static void cfq_deactivate_request(request_queue_t *q, struct request *rq)
@ -684,6 +725,7 @@ __cfq_set_active_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
cfq_clear_cfqq_must_alloc_slice(cfqq);
cfq_clear_cfqq_fifo_expire(cfqq);
cfq_mark_cfqq_slice_new(cfqq);
cfqq->rr_tick = cfqd->cur_rr_tick;
}
cfqd->active_queue = cfqq;
@ -786,10 +828,46 @@ static int cfq_get_next_prio_level(struct cfq_data *cfqd)
cfqd->cur_end_prio = 0;
}
cfqd->cur_rr_tick++;
cfqd->prio_time = jiffies;
return prio;
}
static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd)
static inline sector_t cfq_dist_from_last(struct cfq_data *cfqd,
struct request *rq)
{
if (rq->sector >= cfqd->last_position)
return rq->sector - cfqd->last_position;
else
return cfqd->last_position - rq->sector;
}
static struct cfq_queue *cfq_get_best_queue(struct cfq_data *cfqd)
{
struct cfq_queue *cfqq = NULL, *__cfqq;
sector_t best = -1, dist;
list_for_each_entry(__cfqq, &cfqd->cur_rr, cfq_list) {
if (!__cfqq->next_rq || !cfq_cfqq_sync(__cfqq))
continue;
dist = cfq_dist_from_last(cfqd, __cfqq->next_rq);
if (dist < best) {
best = dist;
cfqq = __cfqq;
}
}
/*
* Only async queue(s) available, grab first entry
*/
if (!cfqq)
cfqq = list_entry_cfqq(cfqd->cur_rr.next);
return cfqq;
}
static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)
{
struct cfq_queue *cfqq = NULL;
@ -799,7 +877,7 @@ static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd)
* empty, get next prio level and grab first entry then if any
* are spliced
*/
cfqq = list_entry_cfqq(cfqd->cur_rr.next);
cfqq = cfq_get_best_queue(cfqd);
} else if (!list_empty(&cfqd->busy_rr)) {
/*
* If no new queues are available, check if the busy list has
@ -820,49 +898,128 @@ static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd)
mod_timer(&cfqd->idle_class_timer, end);
}
return cfqq;
}
static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd)
{
struct cfq_queue *cfqq;
do {
long prio;
cfqq = cfq_get_next_queue(cfqd);
if (!cfqq)
break;
prio = cfq_prio_to_slice(cfqd, cfqq);
if (cfqq->slice_resid > -prio)
break;
cfqq->slice_resid += prio;
list_del_init(&cfqq->cfq_list);
list_add_tail(&cfqq->cfq_list, &cfqd->rr_list[cfqq->ioprio]);
cfqq = NULL;
} while (1);
__cfq_set_active_queue(cfqd, cfqq);
return cfqq;
}
#define CIC_SEEKY(cic) ((cic)->seek_mean > (128 * 1024))
static inline int cfq_rq_close(struct cfq_data *cfqd, struct request *rq)
{
struct cfq_io_context *cic = cfqd->active_cic;
static int cfq_arm_slice_timer(struct cfq_data *cfqd)
if (!sample_valid(cic->seek_samples))
return 0;
return cfq_dist_from_last(cfqd, rq) <= cic->seek_mean;
}
static struct cfq_queue *__cfq_close_cooperator(struct cfq_data *cfqd,
struct cfq_queue *cur_cfqq,
struct list_head *list)
{
struct cfq_queue *cfqq;
list_for_each_entry(cfqq, list, cfq_list) {
if (cfqq == cur_cfqq || !cfq_cfqq_sync(cfqq))
continue;
BUG_ON(!cfqq->next_rq);
if (cfq_rq_close(cfqd, cfqq->next_rq))
return cfqq;
}
return NULL;
}
static int cfq_close_cooperator(struct cfq_data *cfqd,
struct cfq_queue *cur_cfqq)
{
struct cfq_queue *cfqq;
if (!cfqd->busy_queues)
return 0;
/*
* check cur_rr and same-prio rr_list for candidates
*/
cfqq = __cfq_close_cooperator(cfqd, cur_cfqq, &cfqd->cur_rr);
if (cfqq)
return 1;
cfqq = __cfq_close_cooperator(cfqd, cur_cfqq, &cfqd->rr_list[cur_cfqq->ioprio]);
if (cfqq && (cfqq->rr_tick == cfqd->cur_rr_tick))
cfqq = NULL;
return cfqq != NULL;
}
#define CIC_SEEKY(cic) ((cic)->seek_mean > (8 * 1024))
static void cfq_arm_slice_timer(struct cfq_data *cfqd)
{
struct cfq_queue *cfqq = cfqd->active_queue;
struct cfq_io_context *cic;
unsigned long sl;
WARN_ON(!RB_EMPTY_ROOT(&cfqq->sort_list));
WARN_ON(cfq_cfqq_slice_new(cfqq));
/*
* idle is disabled, either manually or by past process history
*/
if (!cfqd->cfq_slice_idle)
return 0;
if (!cfq_cfqq_idle_window(cfqq))
return 0;
if (!cfqd->cfq_slice_idle || !cfq_cfqq_idle_window(cfqq))
return;
/*
* task has exited, don't wait
*/
cic = cfqd->active_cic;
if (!cic || !cic->ioc->task)
return 0;
return;
/*
* See if this prio level has a good candidate
*/
if (cfq_close_cooperator(cfqd, cfqq))
return;
cfq_mark_cfqq_must_dispatch(cfqq);
cfq_mark_cfqq_wait_request(cfqq);
sl = min(cfqq->slice_end - 1, (unsigned long) cfqd->cfq_slice_idle);
/*
* we don't want to idle for seeks, but we do want to allow
* fair distribution of slice time for a process doing back-to-back
* seeks. so allow a little bit of time for him to submit a new rq
*/
sl = cfqd->cfq_slice_idle;
if (sample_valid(cic->seek_samples) && CIC_SEEKY(cic))
sl = min(sl, msecs_to_jiffies(2));
mod_timer(&cfqd->idle_slice_timer, jiffies + sl);
return 1;
}
static void cfq_dispatch_insert(request_queue_t *q, struct request *rq)
@ -870,7 +1027,7 @@ static void cfq_dispatch_insert(request_queue_t *q, struct request *rq)
struct cfq_queue *cfqq = RQ_CFQQ(rq);
cfq_remove_request(rq);
cfqq->on_dispatch[rq_is_sync(rq)]++;
cfqq->dispatched++;
elv_dispatch_sort(q, rq);
}
@ -891,13 +1048,13 @@ static inline struct request *cfq_check_fifo(struct cfq_queue *cfqq)
if (list_empty(&cfqq->fifo))
return NULL;
fifo = cfq_cfqq_class_sync(cfqq);
fifo = cfq_cfqq_sync(cfqq);
rq = rq_entry_fifo(cfqq->fifo.next);
if (time_after(jiffies, rq->start_time + cfqd->cfq_fifo_expire[fifo]))
return rq;
if (time_before(jiffies, rq->start_time + cfqd->cfq_fifo_expire[fifo]))
return NULL;
return NULL;
return rq;
}
static inline int
@ -922,23 +1079,26 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
goto new_queue;
/*
* slice has expired
* The active queue has run out of time, expire it and select new.
*/
if (!cfq_cfqq_must_dispatch(cfqq) && cfq_slice_used(cfqq))
if (cfq_slice_used(cfqq))
goto expire;
/*
* if queue has requests, dispatch one. if not, check if
* enough slice is left to wait for one
* The active queue has requests and isn't expired, allow it to
* dispatch.
*/
if (!RB_EMPTY_ROOT(&cfqq->sort_list))
goto keep_queue;
else if (cfq_cfqq_slice_new(cfqq) || cfq_cfqq_dispatched(cfqq)) {
/*
* No requests pending. If the active queue still has requests in
* flight or is idling for a new request, allow either of these
* conditions to happen (or time out) before selecting a new queue.
*/
if (cfqq->dispatched || timer_pending(&cfqd->idle_slice_timer)) {
cfqq = NULL;
goto keep_queue;
} else if (cfq_cfqq_class_sync(cfqq)) {
if (cfq_arm_slice_timer(cfqd))
return NULL;
}
expire:
@ -1039,7 +1199,7 @@ static int
cfq_dispatch_requests(request_queue_t *q, int force)
{
struct cfq_data *cfqd = q->elevator->elevator_data;
struct cfq_queue *cfqq, *prev_cfqq;
struct cfq_queue *cfqq;
int dispatched;
if (!cfqd->busy_queues)
@ -1049,23 +1209,19 @@ cfq_dispatch_requests(request_queue_t *q, int force)
return cfq_forced_dispatch(cfqd);
dispatched = 0;
prev_cfqq = NULL;
while ((cfqq = cfq_select_queue(cfqd)) != NULL) {
int max_dispatch;
if (cfqd->busy_queues > 1) {
/*
* Don't repeat dispatch from the previous queue.
*/
if (prev_cfqq == cfqq)
break;
/*
* So we have dispatched before in this round, if the
* next queue has idling enabled (must be sync), don't
* allow it service until the previous have continued.
* allow it service until the previous have completed.
*/
if (cfqd->rq_in_driver && cfq_cfqq_idle_window(cfqq))
if (cfqd->rq_in_driver && cfq_cfqq_idle_window(cfqq) &&
dispatched)
break;
if (cfqq->dispatched >= cfqd->cfq_quantum)
break;
}
@ -1078,7 +1234,6 @@ cfq_dispatch_requests(request_queue_t *q, int force)
max_dispatch = 1;
dispatched += __cfq_dispatch_requests(cfqd, cfqq, max_dispatch);
prev_cfqq = cfqq;
}
return dispatched;
@ -1520,7 +1675,8 @@ cfq_update_io_thinktime(struct cfq_data *cfqd, struct cfq_io_context *cic)
}
static void
cfq_update_io_seektime(struct cfq_io_context *cic, struct request *rq)
cfq_update_io_seektime(struct cfq_data *cfqd, struct cfq_io_context *cic,
struct request *rq)
{
sector_t sdist;
u64 total;
@ -1530,6 +1686,11 @@ cfq_update_io_seektime(struct cfq_io_context *cic, struct request *rq)
else
sdist = cic->last_request_pos - rq->sector;
if (!cic->seek_samples) {
cfqd->new_seek_total = (7*cic->seek_total + (u64)256*sdist) / 8;
cfqd->new_seek_mean = cfqd->new_seek_total / 256;
}
/*
* Don't allow the seek distance to get too large from the
* odd fragment, pagein, etc
@ -1580,13 +1741,16 @@ static int
cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
struct request *rq)
{
struct cfq_queue *cfqq = cfqd->active_queue;
sector_t dist;
struct cfq_queue *cfqq;
if (cfq_class_idle(new_cfqq))
cfqq = cfqd->active_queue;
if (!cfqq)
return 0;
if (!cfqq)
if (cfq_slice_used(cfqq))
return 1;
if (cfq_class_idle(new_cfqq))
return 0;
if (cfq_class_idle(cfqq))
@ -1613,12 +1777,7 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
* if this request is as-good as one we would expect from the
* current cfqq, let it preempt
*/
if (rq->sector > cfqd->last_sector)
dist = rq->sector - cfqd->last_sector;
else
dist = cfqd->last_sector - rq->sector;
if (dist <= cfqd->active_cic->seek_mean)
if (cfq_rq_close(cfqd, rq))
return 1;
return 0;
@ -1656,28 +1815,12 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
if (rq_is_meta(rq))
cfqq->meta_pending++;
/*
* we never wait for an async request and we don't allow preemption
* of an async request. so just return early
*/
if (!rq_is_sync(rq)) {
/*
* sync process issued an async request, if it's waiting
* then expire it and kick rq handling.
*/
if (cic == cfqd->active_cic &&
del_timer(&cfqd->idle_slice_timer)) {
cfq_slice_expired(cfqd, 0, 0);
blk_start_queueing(cfqd->queue);
}
return;
}
cfq_update_io_thinktime(cfqd, cic);
cfq_update_io_seektime(cic, rq);
cfq_update_io_seektime(cfqd, cic, rq);
cfq_update_idle_window(cfqd, cfqq, cic);
cic->last_request_pos = rq->sector + rq->nr_sectors;
cfqq->last_request_pos = cic->last_request_pos;
if (cfqq == cfqd->active_queue) {
/*
@ -1726,13 +1869,11 @@ static void cfq_completed_request(request_queue_t *q, struct request *rq)
now = jiffies;
WARN_ON(!cfqd->rq_in_driver);
WARN_ON(!cfqq->on_dispatch[sync]);
WARN_ON(!cfqq->dispatched);
cfqd->rq_in_driver--;
cfqq->on_dispatch[sync]--;
cfqq->dispatched--;
cfqq->service_last = now;
cfqd->last_sector = rq->hard_sector + rq->hard_nr_sectors;
if (!cfq_class_idle(cfqq))
cfqd->last_end_request = now;
@ -1752,11 +1893,12 @@ static void cfq_completed_request(request_queue_t *q, struct request *rq)
}
if (cfq_slice_used(cfqq))
cfq_slice_expired(cfqd, 0, 1);
else if (sync && RB_EMPTY_ROOT(&cfqq->sort_list)) {
if (!cfq_arm_slice_timer(cfqd))
cfq_schedule_dispatch(cfqd);
}
else if (sync && RB_EMPTY_ROOT(&cfqq->sort_list))
cfq_arm_slice_timer(cfqd);
}
if (!cfqd->rq_in_driver)
cfq_schedule_dispatch(cfqd);
}
/*
@ -2101,7 +2243,6 @@ fail:
/*
* sysfs parts below -->
*/
static ssize_t
cfq_var_show(unsigned int var, char *page)
{