blk-iocost: replace iocg->has_surplus with ->surplus_list

Instead of marking iocgs with surplus with a flag and filtering for them
while walking all active iocgs, build a surpluses list. This doesn't make
much difference now but will help implementing improved donation logic which
will iterate iocgs with surplus multiple times.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 2496674..c1cd66c 100644 (file)
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -494,9 +494,9 @@ struct ioc_gq {
        int                             hweight_gen;
        u32                             hweight_active;
        u32                             hweight_inuse;
-       bool                            has_surplus;
 
        struct list_head                walk_list;
+       struct list_head                surplus_list;
 
        struct wait_queue_head          waitq;
        struct hrtimer                  waitq_timer;
@@ -1507,6 +1507,7 @@ static void ioc_timer_fn(struct timer_list *timer)
        struct ioc *ioc = container_of(timer, struct ioc, timer);
        struct ioc_gq *iocg, *tiocg;
        struct ioc_now now;
+       LIST_HEAD(surpluses);
        int nr_surpluses = 0, nr_shortages = 0, nr_lagging = 0;
        u32 ppm_rthr = MILLION - ioc->params.qos[QOS_RPPM];
        u32 ppm_wthr = MILLION - ioc->params.qos[QOS_WPPM];
@@ -1630,8 +1631,7 @@ static void ioc_timer_fn(struct timer_list *timer)
                /* see whether there's surplus vtime */
                vmin = now.vnow - ioc->margins.max;
 
-               iocg->has_surplus = false;
-
+               WARN_ON_ONCE(!list_empty(&iocg->surplus_list));
                if (!waitqueue_active(&iocg->waitq) &&
                    time_before64(vtime, vmin)) {
                        u64 delta = vmin - vtime;
@@ -1641,7 +1641,7 @@ static void ioc_timer_fn(struct timer_list *timer)
                        atomic64_add(delta, &iocg->done_vtime);
                        /* if usage is sufficiently low, maybe it can donate */
                        if (surplus_adjusted_hweight_inuse(usage, hw_inuse)) {
-                               iocg->has_surplus = true;
+                               list_add(&iocg->surplus_list, &surpluses);
                                nr_surpluses++;
                        }
                } else if (hw_inuse < hw_active) {
@@ -1677,13 +1677,10 @@ static void ioc_timer_fn(struct timer_list *timer)
                goto skip_surplus_transfers;
 
        /* there are both shortages and surpluses, transfer surpluses */
-       list_for_each_entry(iocg, &ioc->active_iocgs, active_list) {
+       list_for_each_entry(iocg, &surpluses, surplus_list) {
                u32 usage, hw_active, hw_inuse, new_hwi, new_inuse;
                int nr_valid = 0;
 
-               if (!iocg->has_surplus)
-                       continue;
-
                /* base the decision on max historical usage */
                for (i = 0, usage = 0; i < NR_USAGE_SLOTS; i++) {
                        if (iocg->usages[i]) {
@@ -1711,6 +1708,10 @@ static void ioc_timer_fn(struct timer_list *timer)
 skip_surplus_transfers:
        commit_weights(ioc);
 
+       /* surplus list should be dissolved after use */
+       list_for_each_entry_safe(iocg, tiocg, &surpluses, surplus_list)
+               list_del_init(&iocg->surplus_list);
+
        /*
         * If q is getting clogged or we're missing too much, we're issuing
         * too much IO and should lower vtime rate.  If we're not missing
@@ -2284,6 +2285,7 @@ static void ioc_pd_init(struct blkg_policy_data *pd)
        atomic64_set(&iocg->active_period, atomic64_read(&ioc->cur_period));
        INIT_LIST_HEAD(&iocg->active_list);
        INIT_LIST_HEAD(&iocg->walk_list);
+       INIT_LIST_HEAD(&iocg->surplus_list);
        iocg->hweight_active = WEIGHT_ONE;
        iocg->hweight_inuse = WEIGHT_ONE;
 
@@ -2320,6 +2322,7 @@ static void ioc_pd_free(struct blkg_policy_data *pd)
                }
 
                WARN_ON_ONCE(!list_empty(&iocg->walk_list));
+               WARN_ON_ONCE(!list_empty(&iocg->surplus_list));
 
                spin_unlock_irqrestore(&ioc->lock, flags);