Re: [PATCH 3/6 v3] cfq-iosched: Introduce vdisktime and io weightfor CFQ queue
From: Shaohua Li
Date: Mon Dec 27 2010 - 21:50:57 EST
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?
> Signed-off-by: Gui Jianfeng <guijianfeng@xxxxxxxxxxxxxx>
> ---
> 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.
> +
> /*
> * 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.
> + 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?
> + } 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.
> 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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