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cfq-iosched: defer slice activation to first request being active

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This better matches what time the queue is actually spending doing
IO.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2007-01-19 11:51:58 +11:00 committed by Jens Axboe
parent 99f9628aba
commit 44f7c16065
1 changed files with 53 additions and 38 deletions
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91
block/cfq-iosched.c
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@ -171,6 +171,7 @@ enum cfqq_state_flags {
CFQ_CFQQ_FLAG_idle_window, /* slice idling enabled */
CFQ_CFQQ_FLAG_prio_changed, /* task priority has changed */
CFQ_CFQQ_FLAG_queue_new, /* queue never been serviced */
CFQ_CFQQ_FLAG_slice_new, /* no requests dispatched in slice */
};
#define CFQ_CFQQ_FNS(name) \
@ -196,6 +197,7 @@ CFQ_CFQQ_FNS(fifo_expire);
CFQ_CFQQ_FNS(idle_window);
CFQ_CFQQ_FNS(prio_changed);
CFQ_CFQQ_FNS(queue_new);
CFQ_CFQQ_FNS(slice_new);
#undef CFQ_CFQQ_FNS
static struct cfq_queue *cfq_find_cfq_hash(struct cfq_data *, unsigned int, unsigned short);
@ -230,6 +232,42 @@ static inline pid_t cfq_queue_pid(struct task_struct *task, int rw, int is_sync)
return CFQ_KEY_ASYNC;
}
/*
* Scale schedule slice based on io priority. Use the sync time slice only
* if a queue is marked sync and has sync io queued. A sync queue with async
* io only, should not get full sync slice length.
*/
static inline int
cfq_prio_to_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
const int base_slice = cfqd->cfq_slice[cfq_cfqq_sync(cfqq)];
WARN_ON(cfqq->ioprio >= IOPRIO_BE_NR);
return base_slice + (base_slice/CFQ_SLICE_SCALE * (4 - cfqq->ioprio));
}
static inline void
cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
cfqq->slice_end = cfq_prio_to_slice(cfqd, cfqq) + jiffies;
}
/*
* We need to wrap this check in cfq_cfqq_slice_new(), since ->slice_end
* isn't valid until the first request from the dispatch is activated
* and the slice time set.
*/
static inline int cfq_slice_used(struct cfq_queue *cfqq)
{
if (cfq_cfqq_slice_new(cfqq))
return 0;
if (time_before(jiffies, cfqq->slice_end))
return 0;
return 1;
}
/*
* Lifted from AS - choose which of rq1 and rq2 that is best served now.
* We choose the request that is closest to the head right now. Distance
@ -632,6 +670,7 @@ __cfq_set_active_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
cfqq->slice_left = 0;
cfq_clear_cfqq_must_alloc_slice(cfqq);
cfq_clear_cfqq_fifo_expire(cfqq);
cfq_mark_cfqq_slice_new(cfqq);
}
cfqd->active_queue = cfqq;
@ -660,7 +699,7 @@ __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
* store what was left of this slice, if the queue idled out
* or was preempted
*/
if (time_after(cfqq->slice_end, now))
if (cfq_slice_used(cfqq))
cfqq->slice_left = cfqq->slice_end - now;
else
cfqq->slice_left = 0;
@ -858,27 +897,6 @@ static inline struct request *cfq_check_fifo(struct cfq_queue *cfqq)
return NULL;
}
/*
* Scale schedule slice based on io priority. Use the sync time slice only
* if a queue is marked sync and has sync io queued. A sync queue with async
* io only, should not get full sync slice length.
*/
static inline int
cfq_prio_to_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
const int base_slice = cfqd->cfq_slice[cfq_cfqq_sync(cfqq)];
WARN_ON(cfqq->ioprio >= IOPRIO_BE_NR);
return base_slice + (base_slice/CFQ_SLICE_SCALE * (4 - cfqq->ioprio));
}
static inline void
cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
cfqq->slice_end = cfq_prio_to_slice(cfqd, cfqq) + jiffies;
}
static inline int
cfq_prio_to_maxrq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
@ -894,7 +912,6 @@ cfq_prio_to_maxrq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
*/
static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
{
unsigned long now = jiffies;
struct cfq_queue *cfqq;
cfqq = cfqd->active_queue;
@ -904,7 +921,7 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
/*
* slice has expired
*/
if (!cfq_cfqq_must_dispatch(cfqq) && time_after(now, cfqq->slice_end))
if (!cfq_cfqq_must_dispatch(cfqq) && cfq_slice_used(cfqq))
goto expire;
/*
@ -913,7 +930,7 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
*/
if (!RB_EMPTY_ROOT(&cfqq->sort_list))
goto keep_queue;
else if (cfq_cfqq_dispatched(cfqq)) {
else if (cfq_cfqq_slice_new(cfqq) || cfq_cfqq_dispatched(cfqq)) {
cfqq = NULL;
goto keep_queue;
} else if (cfq_cfqq_class_sync(cfqq)) {
@ -964,21 +981,16 @@ __cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq,
} while (dispatched < max_dispatch);
/*
* if slice end isn't set yet, set it.
*/
if (!cfqq->slice_end)
cfq_set_prio_slice(cfqd, cfqq);
/*
* expire an async queue immediately if it has used up its slice. idle
* queue always expire after 1 dispatch round.
*/
if ((!cfq_cfqq_sync(cfqq) &&
cfqd->dispatch_slice >= cfq_prio_to_maxrq(cfqd, cfqq)) ||
cfq_class_idle(cfqq) ||
!cfq_cfqq_idle_window(cfqq))
cfq_class_idle(cfqq)) {
cfqq->slice_end = jiffies + 1;
cfq_slice_expired(cfqd, 0);
}
return dispatched;
}
@ -1612,7 +1624,8 @@ static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
BUG_ON(!cfq_cfqq_on_rr(cfqq));
list_move(&cfqq->cfq_list, &cfqd->cur_rr);
cfqq->slice_end = cfqq->slice_left + jiffies;
cfqq->slice_end = 0;
cfq_mark_cfqq_slice_new(cfqq);
}
/*
@ -1722,7 +1735,11 @@ static void cfq_completed_request(request_queue_t *q, struct request *rq)
* or if we want to idle in case it has no pending requests.
*/
if (cfqd->active_queue == cfqq) {
if (time_after(now, cfqq->slice_end))
if (cfq_cfqq_slice_new(cfqq)) {
cfq_set_prio_slice(cfqd, cfqq);
cfq_clear_cfqq_slice_new(cfqq);
}
if (cfq_slice_used(cfqq))
cfq_slice_expired(cfqd, 0);
else if (sync && RB_EMPTY_ROOT(&cfqq->sort_list)) {
if (!cfq_arm_slice_timer(cfqd, cfqq))
@ -1901,12 +1918,10 @@ static void cfq_idle_slice_timer(unsigned long data)
spin_lock_irqsave(cfqd->queue->queue_lock, flags);
if ((cfqq = cfqd->active_queue) != NULL) {
unsigned long now = jiffies;
/*
* expired
*/
if (time_after(now, cfqq->slice_end))
if (cfq_slice_used(cfqq))
goto expire;
/*