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>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index bfb3967..28236f2 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -56,13 +56,7 @@
#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 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_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 @@
unsigned int cfq_slice_idle;
struct list_head cic_list;
+
+ sector_t new_seek_mean;
+ u64 new_seek_total;
};
/*
@@ -133,6 +132,8 @@
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 @@
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 @@
/* various state flags, see below */
unsigned int flags;
+
+ sector_t last_request_pos;
};
enum cfqq_state_flags {
@@ -259,6 +263,8 @@
* easily introduce oscillations.
*/
cfqq->slice_resid = 0;
+
+ cfqq->slice_start = jiffies;
}
/*
@@ -307,7 +313,7 @@
s1 = rq1->sector;
s2 = rq2->sector;
- last = cfqd->last_sector;
+ last = cfqd->last_position;
/*
* by definition, 1KiB is 2 sectors
@@ -398,39 +404,42 @@
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 @@
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 @@
*/
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 @@
*/
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_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 @@
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 @@
* 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 @@
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 @@
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 @@
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 @@
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 @@
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 @@
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 @@
max_dispatch = 1;
dispatched += __cfq_dispatch_requests(cfqd, cfqq, max_dispatch);
- prev_cfqq = cfqq;
}
return dispatched;
@@ -1520,7 +1675,8 @@
}
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 @@
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 @@
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 @@
* 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 @@
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 @@
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 @@
}
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 @@
/*
* sysfs parts below -->
*/
-
static ssize_t
cfq_var_show(unsigned int var, char *page)
{