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SubjectRe: [PATCH 3/6 v3] cfq-iosched: Introduce vdisktime and io weight for CFQ queue
Shaohua Li wrote:
> On Mon, 2010-12-27 at 16:51 +0800, Gui Jianfeng wrote:
>> Introduce vdisktime and io weight for CFQ queue scheduling. Currently, io priority
>> maps to a range [100,1000]. It also gets rid of cfq_slice_offset() logic and makes
>> use the same scheduling algorithm as CFQ group does. This helps for CFQ queue and
>> group scheduling on the same service tree.
> Haven't read the whole series yet. Looks this changes a lot of logic
> even without cgroup support. Did you have test if this changes both
> performance and latency in some mixed workloads?

Hi Shaohua,

I did some tests with different workloads and with idling on or idling off.
I don't see performance drop on my box.

>
>> Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
>> ---
>> block/cfq-iosched.c | 211 ++++++++++++++++++++++++++++++++++++++-------------
>> 1 files changed, 158 insertions(+), 53 deletions(-)
>>
>> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
>> index a2553c0..b598798 100644
>> --- a/block/cfq-iosched.c
>> +++ b/block/cfq-iosched.c
>> @@ -100,10 +100,7 @@ struct cfq_entity {
>> struct cfq_rb_root *service_tree;
>> /* service_tree member */
>> struct rb_node rb_node;
>> - /* service_tree key, represent the position on the tree */
>> - unsigned long rb_key;
>> -
>> - /* group service_tree key */
>> + /* service_tree key */
>> u64 vdisktime;
>> bool is_group_entity;
>> unsigned int weight;
>> @@ -115,6 +112,8 @@ struct cfq_entity {
>> struct cfq_queue {
>> /* The schedule entity */
>> struct cfq_entity cfqe;
>> + /* Reposition time */
>> + unsigned long reposition_time;
>> /* reference count */
>> atomic_t ref;
>> /* various state flags, see below */
>> @@ -313,6 +312,24 @@ struct cfq_data {
>> struct rcu_head rcu;
>> };
>>
>> +/*
>> + * Map io priority(7 ~ 0) to io weight(100 ~ 1000) as follows
>> + * prio 0 1 2 3 4 5 6 7
>> + * weight 1000 868 740 612 484 356 228 100
>> + */
>> +static inline unsigned int cfq_prio_to_weight(unsigned short ioprio)
>> +{
>> + unsigned int step;
>> +
>> + BUG_ON(ioprio >= IOPRIO_BE_NR);
>> +
>> + step = (BLKIO_WEIGHT_MAX - BLKIO_WEIGHT_MIN) / (IOPRIO_BE_NR - 1);
>> + if (ioprio == 0)
>> + return BLKIO_WEIGHT_MAX;
>> +
>> + return BLKIO_WEIGHT_MIN + (IOPRIO_BE_NR - ioprio - 1) * step;
>> +}
>> +
>> static inline struct cfq_queue *
>> cfqq_of_entity(struct cfq_entity *cfqe)
>> {
>> @@ -841,16 +858,6 @@ cfq_find_next_rq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
>> return cfq_choose_req(cfqd, next, prev, blk_rq_pos(last));
>> }
>>
>> -static unsigned long cfq_slice_offset(struct cfq_data *cfqd,
>> - struct cfq_queue *cfqq)
>> -{
>> - /*
>> - * just an approximation, should be ok.
>> - */
>> - return (cfqq->cfqg->nr_cfqq - 1) * (cfq_prio_slice(cfqd, 1, 0) -
>> - cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio));
>> -}
>> -
>> static inline s64
>> entity_key(struct cfq_rb_root *st, struct cfq_entity *entity)
>> {
>> @@ -1199,6 +1206,16 @@ static inline void cfq_put_cfqg(struct cfq_group *cfqg) {}
>>
>> #endif /* GROUP_IOSCHED */
>>
>> +static inline u64 cfq_get_boost(struct cfq_data *cfqd,
>> + struct cfq_entity *cfqe)
>> +{
>> + u64 d = cfqd->cfq_slice[1] << CFQ_SERVICE_SHIFT;
>> +
>> + d = d * BLKIO_WEIGHT_DEFAULT;
>> + do_div(d, BLKIO_WEIGHT_MAX - cfqe->weight + BLKIO_WEIGHT_MIN);
>> + return d;
>> +}
> don't consider sync/async here? for group, we don't have such issue, but
> we need boost sync otherwise.

Ok, we should.

>> +
>> /*
>> * The cfqd->service_trees holds all pending cfq_queue's that have
>> * requests waiting to be processed. It is sorted in the order that
>> @@ -1210,13 +1227,14 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
>> struct cfq_entity *cfqe;
>> struct rb_node **p, *parent;
>> struct cfq_entity *__cfqe;
>> - unsigned long rb_key;
>> - struct cfq_rb_root *service_tree;
>> + struct cfq_rb_root *service_tree, *orig_st;
>> int left;
>> int new_cfqq = 1;
>> int group_changed = 0;
>> + s64 key;
>>
>> cfqe = &cfqq->cfqe;
>> + orig_st = cfqe->service_tree;
>>
>> #ifdef CONFIG_CFQ_GROUP_IOSCHED
>> if (!cfqd->cfq_group_isolation
>> @@ -1224,8 +1242,15 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
>> && cfqq->cfqg && cfqq->cfqg != &cfqd->root_group) {
>> /* Move this cfq to root group */
>> cfq_log_cfqq(cfqd, cfqq, "moving to root group");
>> - if (!RB_EMPTY_NODE(&cfqe->rb_node))
>> + if (!RB_EMPTY_NODE(&cfqe->rb_node)) {
>> cfq_group_service_tree_del(cfqd, cfqq->cfqg);
>> + /*
>> + * Group changed, dequeue this CFQ queue from the
>> + * original service tree.
>> + */
>> + cfq_rb_erase(&cfqe->rb_node, cfqe->service_tree);
>> + orig_st->total_weight -= cfqe->weight;
>> + }
>> cfqq->orig_cfqg = cfqq->cfqg;
>> cfqq->cfqg = &cfqd->root_group;
>> atomic_inc(&cfqd->root_group.ref);
>> @@ -1234,8 +1259,15 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
>> && cfqq_type(cfqq) == SYNC_WORKLOAD && cfqq->orig_cfqg) {
>> /* cfqq is sequential now needs to go to its original group */
>> BUG_ON(cfqq->cfqg != &cfqd->root_group);
>> - if (!RB_EMPTY_NODE(&cfqe->rb_node))
>> + if (!RB_EMPTY_NODE(&cfqe->rb_node)) {
>> cfq_group_service_tree_del(cfqd, cfqq->cfqg);
>> + /*
>> + * Group changed, dequeue this CFQ queue from the
>> + * original service tree.
>> + */
>> + cfq_rb_erase(&cfqe->rb_node, cfqe->service_tree);
>> + orig_st->total_weight -= cfqe->weight;
>> + }
>> cfq_put_cfqg(cfqq->cfqg);
>> cfqq->cfqg = cfqq->orig_cfqg;
>> cfqq->orig_cfqg = NULL;
>> @@ -1246,47 +1278,71 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
>>
>> service_tree = service_tree_for(cfqq->cfqg, cfqq_prio(cfqq),
>> cfqq_type(cfqq));
>> + /*
>> + * For the time being, put the newly added CFQ queue at the end of the
>> + * service tree.
>> + */
> so this should be fixed later? please mark it as a todo.

Ahh, forgot remove this annotation, I'v already boost vdisktime according to it ioprio.

>> + if (RB_EMPTY_NODE(&cfqe->rb_node)) {
>> + /*
>> + * If this CFQ queue moves to another group, the original
>> + * vdisktime makes no sense any more, reset the vdisktime
>> + * here.
>> + */
>> + parent = rb_last(&service_tree->rb);
>> + if (parent) {
>> + u64 boost;
>> + s64 __vdisktime;
>> +
>> + __cfqe = rb_entry_entity(parent);
>> + cfqe->vdisktime = __cfqe->vdisktime + CFQ_IDLE_DELAY;
>> +
>> + /* Give some vdisktime boost according to its weight */
>> + boost = cfq_get_boost(cfqd, cfqe);
>> + __vdisktime = cfqe->vdisktime - boost;
>> + if (__vdisktime > service_tree->min_vdisktime)
>> + cfqe->vdisktime = __vdisktime;
>> + else
>> + cfqe->vdisktime = service_tree->min_vdisktime;
>> + } else
>> + cfqe->vdisktime = service_tree->min_vdisktime;
>> +
>> + goto insert;
>> + }
>> + /*
>> + * Ok, we get here, this CFQ queue is on the service tree, dequeue it
>> + * firstly.
>> + */
>> + cfq_rb_erase(&cfqe->rb_node, cfqe->service_tree);
>> + orig_st->total_weight -= cfqe->weight;
>> +
>> + new_cfqq = 0;
>> +
>> if (cfq_class_idle(cfqq)) {
>> - rb_key = CFQ_IDLE_DELAY;
>> parent = rb_last(&service_tree->rb);
>> if (parent && parent != &cfqe->rb_node) {
>> __cfqe = rb_entry(parent, struct cfq_entity, rb_node);
>> - rb_key += __cfqe->rb_key;
>> + cfqe->vdisktime = __cfqe->vdisktime + CFQ_IDLE_DELAY;
>> } else
>> - rb_key += jiffies;
>> + cfqe->vdisktime = service_tree->min_vdisktime;
>> } else if (!add_front) {
>> /*
>> - * Get our rb key offset. Subtract any residual slice
>> - * value carried from last service. A negative resid
>> - * count indicates slice overrun, and this should position
>> - * the next service time further away in the tree.
>> - */
>> - rb_key = cfq_slice_offset(cfqd, cfqq) + jiffies;
>> - rb_key -= cfqq->slice_resid;
>> - cfqq->slice_resid = 0;
>> - } else {
>> - rb_key = -HZ;
>> - __cfqe = cfq_rb_first(service_tree);
>> - rb_key += __cfqe ? __cfqe->rb_key : jiffies;
>> - }
>> -
>> - if (!RB_EMPTY_NODE(&cfqe->rb_node)) {
>> - new_cfqq = 0;
>> - /*
>> - * same position, nothing more to do
>> + * We charge the CFQ queue by the time this queue runs, and
>> + * repsition it on the service tree.
>> */
>> - if (rb_key == cfqe->rb_key &&
>> - cfqe->service_tree == service_tree)
>> - return;
>> + unsigned int used_sl;
>>
>> - cfq_rb_erase(&cfqe->rb_node, cfqe->service_tree);
>> - cfqe->service_tree = NULL;
>> + used_sl = cfq_cfqq_slice_usage(cfqq);
>> + cfqe->vdisktime += cfq_scale_slice(used_sl, cfqe);
> cfqq->slice_resid could be > 0 or < 0, and the queue can be boosted or
> penalized. Looks the logic is completely removed. This exists in current
> cfq group too, I wonder why?

With vdisktime introduced, vdisktime represents cfqq's position on a service
tree. And vdisktime is decided by the acutal running time by a cfqq. So we
don't need slice_resid any more here.

>
>> + } else {
>> + cfqe->vdisktime = service_tree->min_vdisktime;
>> }
>>
>> +insert:
>> left = 1;
>> parent = NULL;
>> cfqe->service_tree = service_tree;
>> p = &service_tree->rb.rb_node;
>> + key = entity_key(service_tree, cfqe);
>> while (*p) {
>> struct rb_node **n;
>>
>> @@ -1296,7 +1352,7 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
>> /*
>> * sort by key, that represents service time.
>> */
>> - if (time_before(rb_key, __cfqe->rb_key))
>> + if (key < entity_key(service_tree, __cfqe))
>> n = &(*p)->rb_left;
>> else {
>> n = &(*p)->rb_right;
>> @@ -1309,10 +1365,12 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
>> if (left)
>> service_tree->left = &cfqe->rb_node;
>>
>> - cfqe->rb_key = rb_key;
>> rb_link_node(&cfqe->rb_node, parent, p);
>> rb_insert_color(&cfqe->rb_node, &service_tree->rb);
>> + update_min_vdisktime(service_tree);
>> service_tree->count++;
>> + service_tree->total_weight += cfqe->weight;
>> + cfqq->reposition_time = jiffies;
>> if ((add_front || !new_cfqq) && !group_changed)
>> return;
>> cfq_group_service_tree_add(cfqd, cfqq->cfqg);
>> @@ -1414,14 +1472,18 @@ static void cfq_add_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
>> static void cfq_del_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
>> {
>> struct cfq_entity *cfqe;
>> + struct cfq_rb_root *service_tree;
>> +
>> cfq_log_cfqq(cfqd, cfqq, "del_from_rr");
>> BUG_ON(!cfq_cfqq_on_rr(cfqq));
>> cfq_clear_cfqq_on_rr(cfqq);
>>
>> cfqe = &cfqq->cfqe;
>> + service_tree = cfqe->service_tree;
>>
>> if (!RB_EMPTY_NODE(&cfqe->rb_node)) {
>> cfq_rb_erase(&cfqe->rb_node, cfqe->service_tree);
>> + service_tree->total_weight -= cfqe->weight;
>> cfqe->service_tree = NULL;
>> }
>> if (cfqq->p_root) {
>> @@ -2120,23 +2182,35 @@ static void cfq_setup_merge(struct cfq_queue *cfqq, struct cfq_queue *new_cfqq)
>> }
>> }
>>
>> +/*
>> + * The time when a CFQ queue is put onto a service tree is recoreded in
>> + * cfqq->reposition_time. Currently, we check the first priority CFQ queues
>> + * on each service tree, and select the workload type that contain the lowest
>> + * reposition_time CFQ queue among them.
>> + */
>> static enum wl_type_t cfq_choose_wl(struct cfq_data *cfqd,
>> struct cfq_group *cfqg, enum wl_prio_t prio)
>> {
>> struct cfq_entity *cfqe;
>> + struct cfq_queue *cfqq;
>> + unsigned long lowest_start_time;
>> int i;
>> - bool key_valid = false;
>> - unsigned long lowest_key = 0;
>> + bool time_valid = false;
>> enum wl_type_t cur_best = SYNC_NOIDLE_WORKLOAD;
>>
>> + /*
>> + * TODO: We may take io priority into account when choosing a workload
>> + * type. But for the time being just make use of reposition_time only.
>> + */
> not just priority, original rb_key considers sys/async too.

IIUC, in original CFQ, rb_key is cross tree, so we need to take sync/async into
account. But with vdisktime introduced, each service has its own vdisktime space.
So there's no need to consider sync/async here.

>> for (i = 0; i <= SYNC_WORKLOAD; ++i) {
>> - /* select the one with lowest rb_key */
>> cfqe = cfq_rb_first(service_tree_for(cfqg, prio, i));
>> - if (cfqe &&
>> - (!key_valid || time_before(cfqe->rb_key, lowest_key))) {
>> - lowest_key = cfqe->rb_key;
>> + cfqq = cfqq_of_entity(cfqe);
>> + if (cfqe && (!time_valid ||
>> + time_before(cfqq->reposition_time,
>> + lowest_start_time))) {
>> + lowest_start_time = cfqq->reposition_time;
>> cur_best = i;
>> - key_valid = true;
>> + time_valid = true;
>> }
>> }
>
> Thanks,
> Shaohua
>
> --
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--
Regards
Gui Jianfeng


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