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[PATCH] cfq-iosched: many performance fixes
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This is a collection of patches that greatly improve CFQ performance
in some circumstances.

- Change the idling logic to only kick in after a request is done and we
  are deciding what to do. Before the idling included the request service
  time, so it was hard to adjust. Now it's true think/idle time.

- Take advantage of TCQ/NCQ/queueing for seeky sync workloads, but keep
  it in control for sync and sequential (or close to) workloads.

- Expire queues immediately and move on to other busy queues, if we are
  not going to idle after the current one finishes.

- Don't rearm idle timer if there are no busy queues. Just leave the
  system idle.

Signed-off-by: Jens Axboe <[email protected]>
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Jens Axboe authored and Jens Axboe committed Jun 23, 2006
1 parent 35e6077 commit caaa5f9
Showing 1 changed file with 76 additions and 40 deletions.
116 changes: 76 additions & 40 deletions block/cfq-iosched.c
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Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,7 @@ static const int cfq_back_penalty = 2; /* penalty of a backwards seek */
static const int cfq_slice_sync = HZ / 10;
static int cfq_slice_async = HZ / 25;
static const int cfq_slice_async_rq = 2;
static int cfq_slice_idle = HZ / 70;
static int cfq_slice_idle = HZ / 125;

#define CFQ_IDLE_GRACE (HZ / 10)
#define CFQ_SLICE_SCALE (5)
Expand Down Expand Up @@ -906,6 +906,8 @@ static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd)
return cfqq;
}

#define CIC_SEEKY(cic) ((cic)->seek_mean > (128 * 1024))

static int cfq_arm_slice_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)

{
Expand Down Expand Up @@ -939,7 +941,7 @@ static int cfq_arm_slice_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)
* 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
*/
if (sample_valid(cic->seek_samples) && cic->seek_mean > 131072)
if (sample_valid(cic->seek_samples) && CIC_SEEKY(cic))
sl = 2;

mod_timer(&cfqd->idle_slice_timer, jiffies + sl);
Expand Down Expand Up @@ -1038,8 +1040,10 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
*/
if (!RB_EMPTY(&cfqq->sort_list))
goto keep_queue;
else if (cfq_cfqq_class_sync(cfqq) &&
time_before(now, cfqq->slice_end)) {
else if (cfq_cfqq_dispatched(cfqq)) {
cfqq = NULL;
goto keep_queue;
} else if (cfq_cfqq_class_sync(cfqq)) {
if (cfq_arm_slice_timer(cfqd, cfqq))
return NULL;
}
Expand Down Expand Up @@ -1088,8 +1092,7 @@ __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 at least one request was
* sync, use the sync time slice value
* if slice end isn't set yet, set it.
*/
if (!cfqq->slice_end)
cfq_set_prio_slice(cfqd, cfqq);
Expand All @@ -1100,7 +1103,8 @@ __cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq,
*/
if ((!cfq_cfqq_sync(cfqq) &&
cfqd->dispatch_slice >= cfq_prio_to_maxrq(cfqd, cfqq)) ||
cfq_class_idle(cfqq))
cfq_class_idle(cfqq) ||
!cfq_cfqq_idle_window(cfqq))
cfq_slice_expired(cfqd, 0);

return dispatched;
Expand All @@ -1109,17 +1113,19 @@ __cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq,
static int
cfq_forced_dispatch_cfqqs(struct list_head *list)
{
int dispatched = 0;
struct cfq_queue *cfqq, *next;
struct cfq_rq *crq;
int dispatched;

dispatched = 0;
list_for_each_entry_safe(cfqq, next, list, cfq_list) {
while ((crq = cfqq->next_crq)) {
cfq_dispatch_insert(cfqq->cfqd->queue, crq);
dispatched++;
}
BUG_ON(!list_empty(&cfqq->fifo));
}

return dispatched;
}

Expand All @@ -1146,18 +1152,26 @@ static int
cfq_dispatch_requests(request_queue_t *q, int force)
{
struct cfq_data *cfqd = q->elevator->elevator_data;
struct cfq_queue *cfqq;
struct cfq_queue *cfqq, *prev_cfqq;
int dispatched;

if (!cfqd->busy_queues)
return 0;

if (unlikely(force))
return cfq_forced_dispatch(cfqd);

cfqq = cfq_select_queue(cfqd);
if (cfqq) {
dispatched = 0;
prev_cfqq = NULL;
while ((cfqq = cfq_select_queue(cfqd)) != NULL) {
int max_dispatch;

/*
* Don't repeat dispatch from the previous queue.
*/
if (prev_cfqq == cfqq)
break;

cfq_clear_cfqq_must_dispatch(cfqq);
cfq_clear_cfqq_wait_request(cfqq);
del_timer(&cfqd->idle_slice_timer);
Expand All @@ -1166,10 +1180,19 @@ cfq_dispatch_requests(request_queue_t *q, int force)
if (cfq_class_idle(cfqq))
max_dispatch = 1;

return __cfq_dispatch_requests(cfqd, cfqq, max_dispatch);
dispatched += __cfq_dispatch_requests(cfqd, cfqq, max_dispatch);

/*
* If the dispatch cfqq has idling enabled and is still
* the active queue, break out.
*/
if (cfq_cfqq_idle_window(cfqq) && cfqd->active_queue)
break;

prev_cfqq = cfqq;
}

return 0;
return dispatched;
}

/*
Expand Down Expand Up @@ -1375,24 +1398,28 @@ static inline void changed_ioprio(struct cfq_io_context *cic)
{
struct cfq_data *cfqd = cic->key;
struct cfq_queue *cfqq;
if (cfqd) {
spin_lock(cfqd->queue->queue_lock);
cfqq = cic->cfqq[ASYNC];
if (cfqq) {
struct cfq_queue *new_cfqq;
new_cfqq = cfq_get_queue(cfqd, CFQ_KEY_ASYNC,
cic->ioc->task, GFP_ATOMIC);
if (new_cfqq) {
cic->cfqq[ASYNC] = new_cfqq;
cfq_put_queue(cfqq);
}
}
cfqq = cic->cfqq[SYNC];
if (cfqq)
cfq_mark_cfqq_prio_changed(cfqq);

spin_unlock(cfqd->queue->queue_lock);
if (unlikely(!cfqd))
return;

spin_lock(cfqd->queue->queue_lock);

cfqq = cic->cfqq[ASYNC];
if (cfqq) {
struct cfq_queue *new_cfqq;
new_cfqq = cfq_get_queue(cfqd, CFQ_KEY_ASYNC, cic->ioc->task,
GFP_ATOMIC);
if (new_cfqq) {
cic->cfqq[ASYNC] = new_cfqq;
cfq_put_queue(cfqq);
}
}

cfqq = cic->cfqq[SYNC];
if (cfqq)
cfq_mark_cfqq_prio_changed(cfqq);

spin_unlock(cfqd->queue->queue_lock);
}

/*
Expand Down Expand Up @@ -1461,8 +1488,7 @@ cfq_get_queue(struct cfq_data *cfqd, unsigned int key, struct task_struct *tsk,
* set ->slice_left to allow preemption for a new process
*/
cfqq->slice_left = 2 * cfqd->cfq_slice_idle;
if (!cfqd->hw_tag)
cfq_mark_cfqq_idle_window(cfqq);
cfq_mark_cfqq_idle_window(cfqq);
cfq_mark_cfqq_prio_changed(cfqq);
cfq_init_prio_data(cfqq);
}
Expand Down Expand Up @@ -1653,7 +1679,8 @@ cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq,
{
int enable_idle = cfq_cfqq_idle_window(cfqq);

if (!cic->ioc->task || !cfqd->cfq_slice_idle || cfqd->hw_tag)
if (!cic->ioc->task || !cfqd->cfq_slice_idle ||
(cfqd->hw_tag && CIC_SEEKY(cic)))
enable_idle = 0;
else if (sample_valid(cic->ttime_samples)) {
if (cic->ttime_mean > cfqd->cfq_slice_idle)
Expand Down Expand Up @@ -1683,7 +1710,7 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
return 0;

if (!cfqq)
return 1;
return 0;

if (cfq_class_idle(cfqq))
return 1;
Expand Down Expand Up @@ -1715,7 +1742,7 @@ static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
cfqq->slice_left = cfq_prio_to_slice(cfqd, cfqq) / 2;

cfqq->slice_end = cfqq->slice_left + jiffies;
__cfq_slice_expired(cfqd, cfqq, 1);
cfq_slice_expired(cfqd, 1);
__cfq_set_active_queue(cfqd, cfqq);
}

Expand Down Expand Up @@ -1834,11 +1861,23 @@ static void cfq_completed_request(request_queue_t *q, struct request *rq)
cfqq->service_last = now;
cfq_resort_rr_list(cfqq, 0);
}
cfq_schedule_dispatch(cfqd);
}

if (cfq_crq_is_sync(crq))
if (sync)
crq->io_context->last_end_request = now;

/*
* If this is the active queue, check if it needs to be expired,
* 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))
cfq_slice_expired(cfqd, 0);
else if (sync && RB_EMPTY(&cfqq->sort_list)) {
if (!cfq_arm_slice_timer(cfqd, cfqq))
cfq_schedule_dispatch(cfqd);
}
}
}

static struct request *
Expand Down Expand Up @@ -2106,11 +2145,8 @@ static void cfq_idle_slice_timer(unsigned long data)
* only expire and reinvoke request handler, if there are
* other queues with pending requests
*/
if (!cfqd->busy_queues) {
cfqd->idle_slice_timer.expires = min(now + cfqd->cfq_slice_idle, cfqq->slice_end);
add_timer(&cfqd->idle_slice_timer);
if (!cfqd->busy_queues)
goto out_cont;
}

/*
* not expired and it has a request pending, let it dispatch
Expand Down

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