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SubjectRe: [PATCH 5/8 v2] cfq-iosched: Introduce hierarchical scheduling with CFQ queue and group at the same level
Vivek Goyal wrote:
> On Mon, Dec 13, 2010 at 09:45:01AM +0800, Gui Jianfeng wrote:
>> This patch makes CFQ queue and CFQ group schedules at the same level.
>> Consider the following hierarchy:
>>
>> Root
>> / | \
>> q1 q2 G1
>> / \
>> q3 G2
>>
>> q1 q2 and q3 are CFQ queues G1 and G2 are CFQ groups. With this patch, q1,
>> q2 and G1 are scheduling on a same service tree in Root CFQ group. q3 and G2
>> are schedluing under G1. Note, for the time being, CFQ group is treated
>> as "BE and SYNC" workload, and is put on "BE and SYNC" service tree. That
>> means service differentiate only happens in "BE and SYNC" service tree.
>> Later, we may introduce "IO Class" for CFQ group.
>>
>> Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
>> ---
>> block/cfq-iosched.c | 473 ++++++++++++++++++++++++++++++++++----------------
>> 1 files changed, 321 insertions(+), 152 deletions(-)
>>
>> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
>> index 6486956..d90627e 100644
>> --- a/block/cfq-iosched.c
>> +++ b/block/cfq-iosched.c
>> @@ -105,6 +105,9 @@ struct cfq_entity {
>> u64 vdisktime;
>> bool is_group_entity;
>> unsigned int weight;
>> + struct cfq_entity *parent;
>> + /* Reposition time */
>> + unsigned long reposition_time;
>> };
>>
>> /*
>> @@ -113,8 +116,6 @@ 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 */
>> @@ -194,6 +195,9 @@ struct cfq_group {
>> /* number of cfqq currently on this group */
>> int nr_cfqq;
>>
>> + /* number of sub cfq groups */
>> + int nr_subgp;
>> +
>
> Do you really have to maintain separate count for child queue and
> child groups? Will a common count something like nr_children be
> not sufficient.

Currently, nr_subgp is only effective in hierarchical mode, but nr_cfqq work
for both hierarchical and flat mode. So for the time being, we need separate
count for child queues and groups.

>
>> /*
>> * Per group busy queus average. Useful for workload slice calc. We
>> * create the array for each prio class but at run time it is used
>> @@ -229,8 +233,6 @@ struct cfq_group {
>> */
>> struct cfq_data {
>> struct request_queue *queue;
>> - /* Root service tree for cfq_groups */
>> - struct cfq_rb_root grp_service_tree;
>
> I see that you are removing this service tree here and then adding it
> back in patch 7. I think it is confusing. In fact title of patch 7 is
> add flat mode. The fact the flat mode is already supported and we
> are just adding hierarchical mode on top of it. I think this is
> just a matter of better naming and patch organization so that
> it is more clear.

Ok, will merge hierarchical patch and flat patch together.

>
>> struct cfq_group root_group;
>>
>> /*
>> @@ -347,8 +349,6 @@ cfqg_of_entity(struct cfq_entity *cfqe)
>> return NULL;
>> }
>>
>> -static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd);
>> -
>> static struct cfq_rb_root *service_tree_for(struct cfq_group *cfqg,
>> enum wl_prio_t prio,
>> enum wl_type_t type)
>> @@ -638,10 +638,15 @@ static inline unsigned cfq_group_get_avg_queues(struct cfq_data *cfqd,
>> static inline unsigned
>> cfq_group_slice(struct cfq_data *cfqd, struct cfq_group *cfqg)
>> {
>> - struct cfq_rb_root *st = &cfqd->grp_service_tree;
>> struct cfq_entity *cfqe = &cfqg->cfqe;
>> + struct cfq_rb_root *st = cfqe->service_tree;
>>
>> - return cfq_target_latency * cfqe->weight / st->total_weight;
>> + if (st)
>> + return cfq_target_latency * cfqe->weight
>> + / st->total_weight;
>
> Is it still true in hierarchical mode. Previously group used to be
> at the top and there used to be only one service tree for groups so
> st->total_weight represented total weight in the system.
>
> Now with hierarhcy this will not/should not be true. So a group slice
> calculation should be different?

I just keep the original group slice calculation here. I was thinking that
calculate group slice in a hierachical way, this might get a really small
group slice and not sure how it works. So I just keep the original calculation.
Any thoughts?

>
>> + else
>> + /* If this is the root group, give it a full slice. */
>> + return cfq_target_latency;
>> }
>>
>> static inline void
>> @@ -804,17 +809,6 @@ static struct cfq_entity *cfq_rb_first(struct cfq_rb_root *root)
>> return NULL;
>> }
>>
>> -static struct cfq_entity *cfq_rb_first_entity(struct cfq_rb_root *root)
>> -{
>> - if (!root->left)
>> - root->left = rb_first(&root->rb);
>> -
>> - if (root->left)
>> - return rb_entry_entity(root->left);
>> -
>> - return NULL;
>> -}
>> -
>> static void rb_erase_init(struct rb_node *n, struct rb_root *root)
>> {
>> rb_erase(n, root);
>> @@ -888,12 +882,15 @@ __cfq_entity_service_tree_add(struct cfq_rb_root *st, struct cfq_entity *cfqe)
>>
>> rb_link_node(&cfqe->rb_node, parent, node);
>> rb_insert_color(&cfqe->rb_node, &st->rb);
>> +
>> + update_min_vdisktime(st);
>> }
>>
>> static void
>> cfq_entity_service_tree_add(struct cfq_rb_root *st, struct cfq_entity *cfqe)
>> {
>> __cfq_entity_service_tree_add(st, cfqe);
>> + cfqe->reposition_time = jiffies;
>> st->count++;
>> st->total_weight += cfqe->weight;
>> }
>> @@ -901,34 +898,57 @@ cfq_entity_service_tree_add(struct cfq_rb_root *st, struct cfq_entity *cfqe)
>> static void
>> cfq_group_service_tree_add(struct cfq_data *cfqd, struct cfq_group *cfqg)
>> {
>> - struct cfq_rb_root *st = &cfqd->grp_service_tree;
>> struct cfq_entity *cfqe = &cfqg->cfqe;
>> - struct cfq_entity *__cfqe;
>> struct rb_node *n;
>> + struct cfq_entity *entity;
>> + struct cfq_rb_root *st;
>> + struct cfq_group *__cfqg;
>>
>> cfqg->nr_cfqq++;
>> +
>> + /*
>> + * Root group doesn't belongs to any service
>> + */
>> + if (cfqg == &cfqd->root_group)
>> + return;
>
> Can we keep root group on cfqd->grp_service_tree? In hierarchical mode
> there will be only 1 group on grp service tree and in flat mode there
> can be many.

Keep top service tree different for hierarchical mode and flat mode is just
fine to me. If you don't strongly object, I'd to keep the current way. :)

>
>> +
>> if (!RB_EMPTY_NODE(&cfqe->rb_node))
>> return;
>>
>> /*
>> - * Currently put the group at the end. Later implement something
>> - * so that groups get lesser vtime based on their weights, so that
>> - * if group does not loose all if it was not continously backlogged.
>> + * Enqueue this group and its ancestors onto their service tree.
>> */
>> - n = rb_last(&st->rb);
>> - if (n) {
>> - __cfqe = rb_entry_entity(n);
>> - cfqe->vdisktime = __cfqe->vdisktime + CFQ_IDLE_DELAY;
>> - } else
>> - cfqe->vdisktime = st->min_vdisktime;
>> + while (cfqe && cfqe->parent) {
>> + if (!RB_EMPTY_NODE(&cfqe->rb_node))
>> + return;
>> +
>> + /*
>> + * Currently put the group at the end. Later implement
>> + * something so that groups get lesser vtime based on their
>> + * weights, so that if group does not loose all if it was not
>> + * continously backlogged.
>> + */
>> + st = cfqe->service_tree;
>> + n = rb_last(&st->rb);
>> + if (n) {
>> + entity = rb_entry_entity(n);
>> + cfqe->vdisktime = entity->vdisktime +
>> + CFQ_IDLE_DELAY;
>> + } else
>> + cfqe->vdisktime = st->min_vdisktime;
>>
>> - cfq_entity_service_tree_add(st, cfqe);
>> + cfq_entity_service_tree_add(st, cfqe);
>> + cfqe = cfqe->parent;
>> + __cfqg = cfqg_of_entity(cfqe);
>> + __cfqg->nr_subgp++;
>> + }
>> }
>>
>> static void
>> __cfq_entity_service_tree_del(struct cfq_rb_root *st, struct cfq_entity *cfqe)
>> {
>> cfq_rb_erase(&cfqe->rb_node, st);
>> + update_min_vdisktime(st);
>> }
>>
>> static void
>> @@ -937,27 +957,47 @@ cfq_entity_service_tree_del(struct cfq_rb_root *st, struct cfq_entity *cfqe)
>> if (!RB_EMPTY_NODE(&cfqe->rb_node)) {
>> __cfq_entity_service_tree_del(st, cfqe);
>> st->total_weight -= cfqe->weight;
>> - cfqe->service_tree = NULL;
>> }
>> }
>>
>> static void
>> cfq_group_service_tree_del(struct cfq_data *cfqd, struct cfq_group *cfqg)
>> {
>> - struct cfq_rb_root *st = &cfqd->grp_service_tree;
>> struct cfq_entity *cfqe = &cfqg->cfqe;
>> + struct cfq_group *__cfqg, *p_cfqg;
>>
>> BUG_ON(cfqg->nr_cfqq < 1);
>> cfqg->nr_cfqq--;
>>
>> + /*
>> + * Root group doesn't belongs to any service
>> + */
>> + if (cfqg == &cfqd->root_group)
>> + return;
>> +
>> /* If there are other cfq queues under this group, don't delete it */
>> if (cfqg->nr_cfqq)
>> return;
>>
>> - cfq_log_cfqg(cfqd, cfqg, "del_from_rr group");
>> - cfq_entity_service_tree_del(st, cfqe);
>> - cfqg->saved_workload_slice = 0;
>> - cfq_blkiocg_update_dequeue_stats(&cfqg->blkg, 1);
>> + /* If child group exists, don't dequeue it */
>> + if (cfqg->nr_subgp)
>> + return;
>> +
>> + /*
>> + * Dequeue this group and its ancestors from their service tree.
>> + */
>> + while (cfqe && cfqe->parent) {
>> + __cfqg = cfqg_of_entity(cfqe);
>> + p_cfqg = cfqg_of_entity(cfqe->parent);
>> + cfq_entity_service_tree_del(cfqe->service_tree, cfqe);
>> + cfq_blkiocg_update_dequeue_stats(&__cfqg->blkg, 1);
>> + cfq_log_cfqg(cfqd, __cfqg, "del_from_rr group");
>> + __cfqg->saved_workload_slice = 0;
>> + cfqe = cfqe->parent;
>> + p_cfqg->nr_subgp--;
>> + if (p_cfqg->nr_cfqq || p_cfqg->nr_subgp)
>> + return;
>> + }
>> }
>
> I think one you merge queue/group algorithms, you can use same function
> for adding/deleting queue/group entities and don't have to use separate
> functions for groups?

The CFQ entity adding/deleting for queue/group are almost the same, and I'v
already extract common function to handle it.
cfq_entity_service_tree_add() and cfq_entity_service_tree_del()

>
> [..]
>> - cfqg->cfqe.weight = blkcg_get_weight(blkcg, cfqg->blkg.dev);
>> +int cfqg_chain_alloc(struct cfq_data *cfqd, struct cgroup *cgroup)
>> +{
>> + struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);
>> + struct blkio_cgroup *p_blkcg;
>> + struct backing_dev_info *bdi = &cfqd->queue->backing_dev_info;
>> + unsigned int major, minor;
>> + struct cfq_group *cfqg, *p_cfqg;
>> + void *key = cfqd;
>> + int ret;
>>
>> - /* Add group on cfqd list */
>> - hlist_add_head(&cfqg->cfqd_node, &cfqd->cfqg_list);
>> + cfqg = cfqg_of_blkg(blkiocg_lookup_group(blkcg, key));
>> + if (cfqg) {
>> + if (!cfqg->blkg.dev && bdi->dev && dev_name(bdi->dev)) {
>> + sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
>> + cfqg->blkg.dev = MKDEV(major, minor);
>> + }
>> + /* chain has already been built */
>> + return 0;
>> + }
>> +
>> + cfqg = kzalloc_node(sizeof(*cfqg), GFP_ATOMIC, cfqd->queue->node);
>> + if (!cfqg)
>> + return -1;
>> +
>> + init_cfqg(cfqd, blkcg, cfqg);
>> +
>> + /* Already to the top group */
>> + if (!cgroup->parent)
>> + return 0;
>> +
>> + /* Allocate CFQ groups on the chain */
>> + ret = cfqg_chain_alloc(cfqd, cgroup->parent);
>
> Can you avoid recursion and user for/while loops to initialize the
> chain. Don't want to push multiple stack frames in case of a deep hier.
>

OK, will change.

>> + if (ret == -1) {
>> + uninit_cfqg(cfqd, cfqg);
>> + return -1;
>> + }
>> +
>> + p_blkcg = cgroup_to_blkio_cgroup(cgroup->parent);
>> + p_cfqg = cfqg_of_blkg(blkiocg_lookup_group(p_blkcg, key));
>> + BUG_ON(p_cfqg == NULL);
>> +
>> + cfqg_set_parent(cfqd, cfqg, p_cfqg);
>> + return 0;
>> +}
>> +
>> +static struct cfq_group *
>> +cfq_find_alloc_cfqg(struct cfq_data *cfqd, struct cgroup *cgroup, int create)
>> +{
>> + struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);
>> + struct cfq_group *cfqg = NULL;
>> + void *key = cfqd;
>> + struct backing_dev_info *bdi = &cfqd->queue->backing_dev_info;
>> + unsigned int major, minor;
>> + int ret;
>> +
>> + cfqg = cfqg_of_blkg(blkiocg_lookup_group(blkcg, key));
>> + if (cfqg && !cfqg->blkg.dev && bdi->dev && dev_name(bdi->dev)) {
>> + sscanf(dev_name(bdi->dev), "%u:%u", &major, &minor);
>> + cfqg->blkg.dev = MKDEV(major, minor);
>> + goto done;
>> + }
>> + if (cfqg || !create)
>> + goto done;
>> +
>> + /*
>> + * For hierarchical cfq group scheduling, we need to allocate
>> + * the whole cfq group chain.
>> + */
>> + ret = cfqg_chain_alloc(cfqd, cgroup);
>> + if (!ret) {
>> + cfqg = cfqg_of_blkg(blkiocg_lookup_group(blkcg, key));
>> + BUG_ON(cfqg == NULL);
>> + goto done;
>> + }
>>
>> done:
>> return cfqg;
>> @@ -1140,12 +1278,22 @@ static void cfq_put_cfqg(struct cfq_group *cfqg)
>> {
>> struct cfq_rb_root *st;
>> int i, j;
>> + struct cfq_entity *cfqe;
>> + struct cfq_group *p_cfqg;
>>
>> BUG_ON(atomic_read(&cfqg->ref) <= 0);
>> if (!atomic_dec_and_test(&cfqg->ref))
>> return;
>> for_each_cfqg_st(cfqg, i, j, st)
>> BUG_ON(!RB_EMPTY_ROOT(&st->rb));
>> +
>> + cfqe = &cfqg->cfqe;
>> + if (cfqe->parent) {
>> + p_cfqg = cfqg_of_entity(cfqe->parent);
>> + /* Drop the reference taken by children */
>> + atomic_dec(&p_cfqg->ref);
>> + }
>> +
>
> Is it the right way to free up whole of the parent chain. just think that
> in a hier of test1->test2->test3 somebody drops the reference to test3
> and test1 and test2 don't have any other children. In that case after
> freeing up test3, we should be freeing up test2 and test1 also.
>
> I was thiking that we can achieve this by freeing up groups in a
> loop.
>
> do {
> cfqe = cfqg->entity.parent;
> if (!atomic_dec_and_test(&cfqg->ref))
> return;
> kfree(cfqg);
> cfqg = cfqg_of_entity(cfqe);
> } while(cfqg)
>

OK

>> kfree(cfqg);
>> }
>>
>> @@ -1358,8 +1506,6 @@ insert:
>> /* Add cfqq onto service tree. */
>> cfq_entity_service_tree_add(service_tree, cfqe);
>>
>> - update_min_vdisktime(service_tree);
>> - cfqq->reposition_time = jiffies;
>> if ((add_front || !new_cfqq) && !group_changed)
>> return;
>> cfq_group_service_tree_add(cfqd, cfqq->cfqg);
>> @@ -1802,28 +1948,30 @@ static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)
>> return cfqq_of_entity(cfq_rb_first(service_tree));
>> }
>>
>> -static struct cfq_queue *cfq_get_next_queue_forced(struct cfq_data *cfqd)
>> +static struct cfq_entity *
>> +cfq_get_next_entity_forced(struct cfq_data *cfqd, struct cfq_group *cfqg)
>> {
>> - struct cfq_group *cfqg;
>> - struct cfq_entity *cfqe;
>> + struct cfq_entity *entity;
>> int i, j;
>> struct cfq_rb_root *st;
>>
>> if (!cfqd->rq_queued)
>> return NULL;
>>
>> - cfqg = cfq_get_next_cfqg(cfqd);
>> - if (!cfqg)
>> - return NULL;
>> -
>> for_each_cfqg_st(cfqg, i, j, st) {
>> - cfqe = cfq_rb_first(st);
>> - if (cfqe != NULL)
>> - return cfqq_of_entity(cfqe);
>> + entity = cfq_rb_first(st);
>> +
>> + if (entity && !entity->is_group_entity)
>> + return entity;
>> + else if (entity && entity->is_group_entity) {
>> + cfqg = cfqg_of_entity(entity);
>> + return cfq_get_next_entity_forced(cfqd, cfqg);
>> + }
>> }
>> return NULL;
>> }
>
> Can above be siplified by just taking cfqd as parameter. Will work both
> for hierarchical and flat mode. Wanted to avoid recursion as somebody
> can create deep cgroup hierarchy and push lots of frames on stack.

Ok, will change.

>
> struct cfq_entity *cfq_get_next_entity_forced(struct cfq_data *cfqd)
> {
> struct service_tree *st = cfqd->grp_service_tree;
>
> do {
> cfqe = cfq_rb_first(st);
> if (is_cfqe_cfqq(cfqe))
> return cfqe;
> st = choose_service_tree_forced(cfqg);
> } while (st);
> }
>
> And choose_service_tree_forced() can be something like.
>
> choose_service_tree_forced(cfqg) {
> for_each_cfqg_st() {
> if (st->count !=0)
> return st;
> }
> }
>
>>
>> +
>> /*
>> * Get and set a new active queue for service.
>> */
>> @@ -2179,7 +2327,6 @@ 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 time_valid = false;
>> @@ -2191,10 +2338,9 @@ static enum wl_type_t cfq_choose_wl(struct cfq_data *cfqd,
>> */
>> for (i = 0; i <= SYNC_WORKLOAD; ++i) {
>> cfqe = cfq_rb_first(service_tree_for(cfqg, prio, i));
>> - cfqq = cfqq_of_entity(cfqe);
>> if (cfqe && (!time_valid ||
>> - cfqq->reposition_time < lowest_start_time)) {
>> - lowest_start_time = cfqq->reposition_time;
>> + cfqe->reposition_time < lowest_start_time)) {
>> + lowest_start_time = cfqe->reposition_time;
>> cur_best = i;
>> time_valid = true;
>> }
>> @@ -2203,47 +2349,13 @@ static enum wl_type_t cfq_choose_wl(struct cfq_data *cfqd,
>> return cur_best;
>> }
>>
>> -static void choose_service_tree(struct cfq_data *cfqd, struct cfq_group *cfqg)
>> +static void set_workload_expire(struct cfq_data *cfqd, struct cfq_group *cfqg)
>> {
>> unsigned slice;
>> unsigned count;
>> struct cfq_rb_root *st;
>> unsigned group_slice;
>>
>> - if (!cfqg) {
>> - cfqd->serving_prio = IDLE_WORKLOAD;
>> - cfqd->workload_expires = jiffies + 1;
>> - return;
>> - }
>> -
>> - /* Choose next priority. RT > BE > IDLE */
>> - if (cfq_group_busy_queues_wl(RT_WORKLOAD, cfqd, cfqg))
>> - cfqd->serving_prio = RT_WORKLOAD;
>> - else if (cfq_group_busy_queues_wl(BE_WORKLOAD, cfqd, cfqg))
>> - 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
>> - */
>> - st = service_tree_for(cfqg, cfqd->serving_prio, cfqd->serving_type);
>> - count = st->count;
>> -
>> - /*
>> - * check workload expiration, and that we still have other queues ready
>> - */
>> - if (count && !time_after(jiffies, cfqd->workload_expires))
>> - return;
>> -
>> - /* otherwise select new workload type */
>> - cfqd->serving_type =
>> - cfq_choose_wl(cfqd, cfqg, cfqd->serving_prio);
>> st = service_tree_for(cfqg, cfqd->serving_prio, cfqd->serving_type);
>> count = st->count;
>>
>> @@ -2284,26 +2396,51 @@ static void choose_service_tree(struct cfq_data *cfqd, struct cfq_group *cfqg)
>> cfqd->workload_expires = jiffies + slice;
>> }
>>
>> -static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd)
>> +static void choose_service_tree(struct cfq_data *cfqd, struct cfq_group *cfqg)
>> {
>> - struct cfq_rb_root *st = &cfqd->grp_service_tree;
>> - struct cfq_group *cfqg;
>> - struct cfq_entity *cfqe;
>> + struct cfq_rb_root *st;
>> + unsigned count;
>>
>> - if (RB_EMPTY_ROOT(&st->rb))
>> - return NULL;
>> - cfqe = cfq_rb_first_entity(st);
>> - cfqg = cfqg_of_entity(cfqe);
>> - BUG_ON(!cfqg);
>> - update_min_vdisktime(st);
>> - return cfqg;
>> + if (!cfqg) {
>> + cfqd->serving_prio = IDLE_WORKLOAD;
>> + cfqd->workload_expires = jiffies + 1;
>> + return;
>> + }
>
> I am wondering where do we use above code. Do we ever call
> choose_service_tree() with cfqg == NULL? Can't seem to figure out by
> looking at the code.

Already fixed by a seperate patch. ;)

>
>> +
>> + /* Choose next priority. RT > BE > IDLE */
>> + if (cfq_group_busy_queues_wl(RT_WORKLOAD, cfqd, cfqg))
>> + cfqd->serving_prio = RT_WORKLOAD;
>> + else if (cfq_group_busy_queues_wl(BE_WORKLOAD, cfqd, cfqg))
>> + 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
>> + */
>> + st = service_tree_for(cfqg, cfqd->serving_prio, cfqd->serving_type);
>> + count = st->count;
>> +
>> + /*
>> + * check workload expiration, and that we still have other queues ready
>> + */
>> + if (count && !time_after(jiffies, cfqd->workload_expires))
>> + return;
>> +
>> + /* otherwise select new workload type */
>> + cfqd->serving_type =
>> + cfq_choose_wl(cfqd, cfqg, cfqd->serving_prio);
>> }
>>
>> -static void cfq_choose_cfqg(struct cfq_data *cfqd)
>> +struct cfq_entity *choose_serving_entity(struct cfq_data *cfqd,
>> + struct cfq_group *cfqg)
>
> I think for this function you don't have to pass cfqg as parameter. You
> can just use cfqd as parameter and then take all decisions based on
> service tree.
>
> So at top we can continue to have grp_service_tree in cfqd. In
> hierarchical mode it will only have root group queued there and in
> flat mode it can have multiple groups queued.
>
> Also I am looking forward to simplifying and organizing CFQ code little
> better so that it is easy to read. Can chooser_serving entity function
> be organized something as follows. This shoudl work both for flat and
> hierarchical modes. Following is only a pesudo code.
>
> struct cfq_entity *select_entity(struct cfq_data *cfqd)
> {
> struct cfq_rb_root *st = cfqd->grp_service_tree;
> struct cfq_entity *cfqe;
>
> do {
> cfqe = cfq_rb_first(st);
> if (is_cfqe_cfqq(cfqe))
> /* We found the next queue to dispatch from */
> break;
> else
> st = choose_service_tree();
> } while (st)
>
> return cfqe;
> }
>

Ok, I'll refine the code to make it easier to read.

>> {
>> - struct cfq_group *cfqg = cfq_get_next_cfqg(cfqd);
>> -
>> - cfqd->serving_group = cfqg;
>> + struct cfq_rb_root *service_tree;
>>
>> /* Restore the workload type data */
>> if (cfqg->saved_workload_slice) {
>> @@ -2314,8 +2451,21 @@ static void cfq_choose_cfqg(struct cfq_data *cfqd)
>> cfqd->workload_expires = jiffies - 1;
>>
>> choose_service_tree(cfqd, cfqg);
>> -}
>>
>> + service_tree = service_tree_for(cfqg, cfqd->serving_prio,
>> + cfqd->serving_type);
>> +
>> + if (!cfqd->rq_queued)
>> + return NULL;
>> +
>> + /* There is nothing to dispatch */
>> + if (!service_tree)
>> + return NULL;
>> + if (RB_EMPTY_ROOT(&service_tree->rb))
>> + return NULL;
>> +
>> + return cfq_rb_first(service_tree);
>> +}
>> /*
>> * 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.
>> @@ -2323,6 +2473,8 @@ static void cfq_choose_cfqg(struct cfq_data *cfqd)
>> static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
>> {
>> struct cfq_queue *cfqq, *new_cfqq = NULL;
>> + struct cfq_group *cfqg;
>> + struct cfq_entity *entity;
>>
>> cfqq = cfqd->active_queue;
>> if (!cfqq)
>> @@ -2422,8 +2574,23 @@ new_queue:
>> * Current queue expired. Check if we have to switch to a new
>> * service tree
>> */
>> - if (!new_cfqq)
>> - cfq_choose_cfqg(cfqd);
>> + cfqg = &cfqd->root_group;
>> +
>> + if (!new_cfqq) {
>> + do {
>> + entity = choose_serving_entity(cfqd, cfqg);
>> + if (entity && !entity->is_group_entity) {
>> + /* This is the CFQ queue that should run */
>> + new_cfqq = cfqq_of_entity(entity);
>> + cfqd->serving_group = cfqg;
>> + set_workload_expire(cfqd, cfqg);
>> + break;
>> + } else if (entity && entity->is_group_entity) {
>> + /* Continue to lookup in this CFQ group */
>> + cfqg = cfqg_of_entity(entity);
>> + }
>> + } while (entity && entity->is_group_entity);
>
> I think move above logic in a separate function otherwise select_queue()
> is becoming complicated.
>
> Secondly for traversing the hierarchy you can introduce macros like
> for_each_entity() or for_each_cfqe() etc.
>
> Thirdly I would again say that flat mode is already supported. Build on
> top of it instead of first getting rid of it and then adding it back
> with the help of a separate patch. If it is too complicated then let
> it be a single patch instead of separating it out in two pathes.

Ok

Thanks for reviewing Vievk, will post a updated patch.

Gui

>
>> + }
>
>>
>> cfqq = cfq_set_active_queue(cfqd, new_cfqq);
>> keep_queue:
>> @@ -2454,10 +2621,14 @@ static int cfq_forced_dispatch(struct cfq_data *cfqd)
>> {
>> struct cfq_queue *cfqq;
>> int dispatched = 0;
>> + struct cfq_entity *entity;
>> + struct cfq_group *root = &cfqd->root_group;
>>
>> /* Expire the timeslice of the current active queue first */
>> cfq_slice_expired(cfqd, 0);
>> - while ((cfqq = cfq_get_next_queue_forced(cfqd)) != NULL) {
>> + while ((entity = cfq_get_next_entity_forced(cfqd, root)) != NULL) {
>> + BUG_ON(entity->is_group_entity);
>> + cfqq = cfqq_of_entity(entity);
>> __cfq_set_active_queue(cfqd, cfqq);
>> dispatched += __cfq_forced_dispatch_cfqq(cfqq);
>> }
>> @@ -3991,9 +4162,6 @@ static void *cfq_init_queue(struct request_queue *q)
>>
>> cfqd->cic_index = i;
>>
>> - /* Init root service tree */
>> - cfqd->grp_service_tree = CFQ_RB_ROOT;
>> -
>> /* Init root group */
>> cfqg = &cfqd->root_group;
>> for_each_cfqg_st(cfqg, i, j, st)
>> @@ -4003,6 +4171,7 @@ static void *cfq_init_queue(struct request_queue *q)
>> /* Give preference to root group over other groups */
>> cfqg->cfqe.weight = 2*BLKIO_WEIGHT_DEFAULT;
>> cfqg->cfqe.is_group_entity = true;
>> + cfqg->cfqe.parent = NULL;
>>
>> #ifdef CONFIG_CFQ_GROUP_IOSCHED
>> /*
>> --
>> 1.6.5.2
>>
>>
>


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