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: Corrado Zoccolo <czoccolo@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Corrado Zoccolo 2009-10-26 22:45:29 +01:00 committed by Jens Axboe
parent a6d44e982d
commit 718eee0579

View file

@ -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
* 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(cfqq->seek_samples) && CFQQ_SEEKY(cfqq))
/* 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.
*/
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;
@ -1432,10 +1564,12 @@ 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)
dispatched += __cfq_forced_dispatch_cfqq(cfqq);
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)
dispatched += __cfq_forced_dispatch_cfqq(cfqq);
@ -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;
/*