Commit 718eee05 authored by Corrado Zoccolo's avatar Corrado Zoccolo Committed by Jens Axboe
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cfq-iosched: fairness for sync no-idle queues 



Currently no-idle queues in cfq are not serviced fairly:
even if they can only dispatch a small number of requests at a time,
they have to compete with idling queues to be serviced, experiencing
large latencies.

We should notice, instead, that no-idle queues are the ones that would
benefit most from having low latency, in fact they are any of:
* processes with large think times (e.g. interactive ones like file
  managers)
* seeky (e.g. programs faulting in their code at startup)
* or marked as no-idle from upper levels, to improve latencies of those
  requests.

This patch improves the fairness and latency for those queues, by:
* separating sync idle, sync no-idle and async queues in separate
  service_trees, for each priority
* service all no-idle queues together
* and idling when the last no-idle queue has been serviced, to
  anticipate for more no-idle work
* the timeslices allotted for idle and no-idle service_trees are
  computed proportionally to the number of processes in each set.

Servicing all no-idle queues together should have a performance boost
for NCQ-capable drives, without compromising fairness.

Signed-off-by: default avatarCorrado Zoccolo <czoccolo@gmail.com>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent a6d44e98

block/cfq-iosched.c

+168 −32
Original line number Diff line number Diff line
@@ -134,7 +134,7 @@ struct cfq_queue { 
};



/*

 * Index in the service_trees.

 * First index in the service_trees.

 * IDLE is handled separately, so it has negative index

 */

enum wl_prio_t {
@@ -143,6 +143,16 @@ enum wl_prio_t { 
	RT_WORKLOAD = 1

};



/*

 * Second index in the service_trees.

 */

enum wl_type_t {

	ASYNC_WORKLOAD = 0,

	SYNC_NOIDLE_WORKLOAD = 1,

	SYNC_WORKLOAD = 2

};





/*

 * Per block device queue structure

 */
@@ -153,12 +163,14 @@ struct cfq_data { 
	 * rr lists of queues with requests, onle rr for each priority class.

	 * Counts are embedded in the cfq_rb_root

	 */

	struct cfq_rb_root service_trees[2];

	struct cfq_rb_root service_trees[2][3];

	struct cfq_rb_root service_tree_idle;

	/*

	 * The priority currently being served

	 */

	enum wl_prio_t serving_prio;

	enum wl_type_t serving_type;

	unsigned long workload_expires;



	/*

	 * Each priority tree is sorted by next_request position.  These
@@ -221,12 +233,13 @@ struct cfq_data { 
};



static struct cfq_rb_root *service_tree_for(enum wl_prio_t prio,

					    enum wl_type_t type,

					    struct cfq_data *cfqd)

{

	if (prio == IDLE_WORKLOAD)

		return &cfqd->service_tree_idle;



	return &cfqd->service_trees[prio];

	return &cfqd->service_trees[prio][type];

}



enum cfqq_state_flags {
@@ -282,12 +295,24 @@ static inline enum wl_prio_t cfqq_prio(struct cfq_queue *cfqq) 
	return BE_WORKLOAD;

}





static enum wl_type_t cfqq_type(struct cfq_queue *cfqq)

{

	if (!cfq_cfqq_sync(cfqq))

		return ASYNC_WORKLOAD;

	if (!cfq_cfqq_idle_window(cfqq))

		return SYNC_NOIDLE_WORKLOAD;

	return SYNC_WORKLOAD;

}



static inline int cfq_busy_queues_wl(enum wl_prio_t wl, struct cfq_data *cfqd)

{

	if (wl == IDLE_WORKLOAD)

		return cfqd->service_tree_idle.count;



	return cfqd->service_trees[wl].count;

	return cfqd->service_trees[wl][ASYNC_WORKLOAD].count

		+ cfqd->service_trees[wl][SYNC_NOIDLE_WORKLOAD].count

		+ cfqd->service_trees[wl][SYNC_WORKLOAD].count;

}



static void cfq_dispatch_insert(struct request_queue *, struct request *);
@@ -597,7 +622,7 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq, 
	struct cfq_rb_root *service_tree;

	int left;



	service_tree = service_tree_for(cfqq_prio(cfqq), cfqd);

	service_tree = service_tree_for(cfqq_prio(cfqq), cfqq_type(cfqq), cfqd);

	if (cfq_class_idle(cfqq)) {

		rb_key = CFQ_IDLE_DELAY;

		parent = rb_last(&service_tree->rb);
@@ -1030,7 +1055,7 @@ static inline void cfq_slice_expired(struct cfq_data *cfqd, bool timed_out) 
static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)

{

	struct cfq_rb_root *service_tree =

		service_tree_for(cfqd->serving_prio, cfqd);

		service_tree_for(cfqd->serving_prio, cfqd->serving_type, cfqd);



	if (RB_EMPTY_ROOT(&service_tree->rb))

		return NULL;
@@ -1167,7 +1192,7 @@ static struct cfq_queue *cfq_close_cooperator(struct cfq_data *cfqd, 
static bool cfq_should_idle(struct cfq_data *cfqd, struct cfq_queue *cfqq)

{

	enum wl_prio_t prio = cfqq_prio(cfqq);

	struct cfq_rb_root *service_tree;

	struct cfq_rb_root *service_tree = cfqq->service_tree;



	/* We never do for idle class queues. */

	if (prio == IDLE_WORKLOAD)
@@ -1181,7 +1206,9 @@ static bool cfq_should_idle(struct cfq_data *cfqd, struct cfq_queue *cfqq) 
	 * Otherwise, we do only if they are the last ones

	 * in their service tree.

	 */

	service_tree = service_tree_for(prio, cfqd);

	if (!service_tree)

		service_tree = service_tree_for(prio, cfqq_type(cfqq), cfqd);



	if (service_tree->count == 0)

		return true;
@@ -1235,14 +1262,20 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd) 


	cfq_mark_cfqq_wait_request(cfqq);



	/*

	 * we don't want to idle for seeks, but we do want to allow

	sl = cfqd->cfq_slice_idle;

	/* are we servicing noidle tree, and there are more queues?

	 * non-rotational or NCQ: no idle

	 * non-NCQ rotational : very small idle, 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

	 *     seeks.

	 */

	sl = cfqd->cfq_slice_idle;

	if (sample_valid(cfqq->seek_samples) && CFQQ_SEEKY(cfqq))

	if (cfqd->serving_type == SYNC_NOIDLE_WORKLOAD &&

	    service_tree_for(cfqd->serving_prio, SYNC_NOIDLE_WORKLOAD, cfqd)

		->count > 0) {

		if (blk_queue_nonrot(cfqd->queue) || cfqd->hw_tag)

			return;

		sl = min(sl, msecs_to_jiffies(CFQ_MIN_TT));

	}



	mod_timer(&cfqd->idle_slice_timer, jiffies + sl);

	cfq_log_cfqq(cfqd, cfqq, "arm_idle: %lu", sl);
@@ -1346,6 +1379,106 @@ static void cfq_setup_merge(struct cfq_queue *cfqq, struct cfq_queue *new_cfqq) 
	}

}



static enum wl_type_t cfq_choose_wl(struct cfq_data *cfqd, enum wl_prio_t prio,

				    bool prio_changed)

{

	struct cfq_queue *queue;

	int i;

	bool key_valid = false;

	unsigned long lowest_key = 0;

	enum wl_type_t cur_best = SYNC_NOIDLE_WORKLOAD;



	if (prio_changed) {

		/*

		 * When priorities switched, we prefer starting

		 * from SYNC_NOIDLE (first choice), or just SYNC

		 * over ASYNC

		 */

		if (service_tree_for(prio, cur_best, cfqd)->count)

			return cur_best;

		cur_best = SYNC_WORKLOAD;

		if (service_tree_for(prio, cur_best, cfqd)->count)

			return cur_best;



		return ASYNC_WORKLOAD;

	}



	for (i = 0; i < 3; ++i) {

		/* otherwise, select the one with lowest rb_key */

		queue = cfq_rb_first(service_tree_for(prio, i, cfqd));

		if (queue &&

		    (!key_valid || time_before(queue->rb_key, lowest_key))) {

			lowest_key = queue->rb_key;

			cur_best = i;

			key_valid = true;

		}

	}



	return cur_best;

}



static void choose_service_tree(struct cfq_data *cfqd)

{

	enum wl_prio_t previous_prio = cfqd->serving_prio;

	bool prio_changed;

	unsigned slice;

	unsigned count;



	/* Choose next priority. RT > BE > IDLE */

	if (cfq_busy_queues_wl(RT_WORKLOAD, cfqd))

		cfqd->serving_prio = RT_WORKLOAD;

	else if (cfq_busy_queues_wl(BE_WORKLOAD, cfqd))

		cfqd->serving_prio = BE_WORKLOAD;

	else {

		cfqd->serving_prio = IDLE_WORKLOAD;

		cfqd->workload_expires = jiffies + 1;

		return;

	}



	/*

	 * For RT and BE, we have to choose also the type

	 * (SYNC, SYNC_NOIDLE, ASYNC), and to compute a workload

	 * expiration time

	 */

	prio_changed = (cfqd->serving_prio != previous_prio);

	count = service_tree_for(cfqd->serving_prio, cfqd->serving_type, cfqd)

		->count;



	/*

	 * If priority didn't change, check workload expiration,

	 * and that we still have other queues ready

	 */

	if (!prio_changed && count &&

	    !time_after(jiffies, cfqd->workload_expires))

		return;



	/* otherwise select new workload type */

	cfqd->serving_type =

		cfq_choose_wl(cfqd, cfqd->serving_prio, prio_changed);

	count = service_tree_for(cfqd->serving_prio, cfqd->serving_type, cfqd)

		->count;



	/*

	 * the workload slice is computed as a fraction of target latency

	 * proportional to the number of queues in that workload, over

	 * all the queues in the same priority class

	 */

	slice = cfq_target_latency * count /

		max_t(unsigned, cfqd->busy_queues_avg[cfqd->serving_prio],

		      cfq_busy_queues_wl(cfqd->serving_prio, cfqd));



	if (cfqd->serving_type == ASYNC_WORKLOAD)

		/* async workload slice is scaled down according to

		 * the sync/async slice ratio. */

		slice = slice * cfqd->cfq_slice[0] / cfqd->cfq_slice[1];

	else

		/* sync workload slice is at least 2 * cfq_slice_idle */

		slice = max(slice, 2 * cfqd->cfq_slice_idle);



	slice = max_t(unsigned, slice, CFQ_MIN_TT);

	cfqd->workload_expires = jiffies + slice;

}



/*

 * Select a queue for service. If we have a current active queue,

 * check whether to continue servicing it, or retrieve and set a new one.
@@ -1398,14 +1531,13 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd) 
expire:

	cfq_slice_expired(cfqd, 0);

new_queue:

	if (!new_cfqq) {

		if (cfq_busy_queues_wl(RT_WORKLOAD, cfqd))

			cfqd->serving_prio = RT_WORKLOAD;

		else if (cfq_busy_queues_wl(BE_WORKLOAD, cfqd))

			cfqd->serving_prio = BE_WORKLOAD;

		else

			cfqd->serving_prio = IDLE_WORKLOAD;

	}

	/*

	 * Current queue expired. Check if we have to switch to a new

	 * service tree

	 */

	if (!new_cfqq)

		choose_service_tree(cfqd);



	cfqq = cfq_set_active_queue(cfqd, new_cfqq);

keep_queue:

	return cfqq;
@@ -1432,9 +1564,11 @@ static int cfq_forced_dispatch(struct cfq_data *cfqd) 
{

	struct cfq_queue *cfqq;

	int dispatched = 0;

	int i;

	int i, j;

	for (i = 0; i < 2; ++i)

		while ((cfqq = cfq_rb_first(&cfqd->service_trees[i])) != NULL)

		for (j = 0; j < 3; ++j)

			while ((cfqq = cfq_rb_first(&cfqd->service_trees[i][j]))

				!= NULL)

				dispatched += __cfq_forced_dispatch_cfqq(cfqq);



	while ((cfqq = cfq_rb_first(&cfqd->service_tree_idle)) != NULL)
@@ -2218,13 +2352,10 @@ cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq, 
	enable_idle = old_idle = cfq_cfqq_idle_window(cfqq);



	if (!atomic_read(&cic->ioc->nr_tasks) || !cfqd->cfq_slice_idle ||

	    (!cfqd->cfq_latency && cfqd->hw_tag && CFQQ_SEEKY(cfqq)))

	    (sample_valid(cfqq->seek_samples) && CFQQ_SEEKY(cfqq)))

		enable_idle = 0;

	else if (sample_valid(cic->ttime_samples)) {

		unsigned int slice_idle = cfqd->cfq_slice_idle;

		if (sample_valid(cfqq->seek_samples) && CFQQ_SEEKY(cfqq))

			slice_idle = msecs_to_jiffies(CFQ_MIN_TT);

		if (cic->ttime_mean > slice_idle)

		if (cic->ttime_mean > cfqd->cfq_slice_idle)

			enable_idle = 0;

		else

			enable_idle = 1;
@@ -2262,6 +2393,10 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq, 
	if (cfq_class_idle(cfqq))

		return true;



	if (cfqd->serving_type == SYNC_NOIDLE_WORKLOAD

	    && new_cfqq->service_tree == cfqq->service_tree)

		return true;



	/*

	 * if the new request is sync, but the currently running queue is

	 * not, let the sync request have priority.
@@ -2778,14 +2913,15 @@ static void cfq_exit_queue(struct elevator_queue *e) 
static void *cfq_init_queue(struct request_queue *q)

{

	struct cfq_data *cfqd;

	int i;

	int i, j;



	cfqd = kmalloc_node(sizeof(*cfqd), GFP_KERNEL | __GFP_ZERO, q->node);

	if (!cfqd)

		return NULL;



	for (i = 0; i < 2; ++i)

		cfqd->service_trees[i] = CFQ_RB_ROOT;

		for (j = 0; j < 3; ++j)

			cfqd->service_trees[i][j] = CFQ_RB_ROOT;

	cfqd->service_tree_idle = CFQ_RB_ROOT;



	/*

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