blkio: Group time used accounting and workload context save restore

o This patch introduces the functionality to do the accounting of group time
  when a queue expires. This time used decides which is the group to go
  next.

o Also introduce the functionlity to save and restore the workload type
  context with-in group. It might happen that once we expire the cfq queue
  and group, a different group will schedule in and we will lose the context
  of the workload type. Hence save and restore it upon queue expiry.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 79 insertions, 0 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 84887e2eb21..55d2a21f7f0 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -115,6 +115,10 @@ struct cfq_queue {
         /* fifo list of requests in sort_list */
         struct list_head fifo;
 
+        /* time when queue got scheduled in to dispatch first request. */
+        unsigned long dispatch_start;
+        /* time when first request from queue completed and slice started. */
+        unsigned long slice_start;
         unsigned long slice_end;
         long slice_resid;
         unsigned int slice_dispatch;
@@ -181,6 +185,10 @@ struct cfq_group {
          */
         struct cfq_rb_root service_trees[2][3];
         struct cfq_rb_root service_tree_idle;
+
+        unsigned long saved_workload_slice;
+        enum wl_type_t saved_workload;
+        enum wl_prio_t saved_serving_prio;
 };
 
 /*
@@ -543,6 +551,7 @@ cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
                                     low_slice);
                 }
         }
+        cfqq->slice_start = jiffies;
         cfqq->slice_end = jiffies + slice;
         cfq_log_cfqq(cfqd, cfqq, "set_slice=%lu", cfqq->slice_end - jiffies);
 }
@@ -818,6 +827,58 @@ cfq_group_service_tree_del(struct cfq_data *cfqd, struct cfq_group *cfqg)
         st->total_weight -= cfqg->weight;
         if (!RB_EMPTY_NODE(&cfqg->rb_node))
                 cfq_rb_erase(&cfqg->rb_node, st);
+        cfqg->saved_workload_slice = 0;
+}
+
+static inline unsigned int cfq_cfqq_slice_usage(struct cfq_queue *cfqq)
+{
+        unsigned int slice_used, allocated_slice;
+
+        /*
+         * Queue got expired before even a single request completed or
+         * got expired immediately after first request completion.
+         */
+        if (!cfqq->slice_start || cfqq->slice_start == jiffies) {
+                /*
+                 * Also charge the seek time incurred to the group, otherwise
+                 * if there are mutiple queues in the group, each can dispatch
+                 * a single request on seeky media and cause lots of seek time
+                 * and group will never know it.
+                 */
+                slice_used = max_t(unsigned, (jiffies - cfqq->dispatch_start),
+                                        1);
+        } else {
+                slice_used = jiffies - cfqq->slice_start;
+                allocated_slice = cfqq->slice_end - cfqq->slice_start;
+                if (slice_used > allocated_slice)
+                        slice_used = allocated_slice;
+        }
+
+        cfq_log_cfqq(cfqq->cfqd, cfqq, "sl_used=%u", slice_used);
+        return slice_used;
+}
+
+static void cfq_group_served(struct cfq_data *cfqd, struct cfq_group *cfqg,
+                                struct cfq_queue *cfqq)
+{
+        struct cfq_rb_root *st = &cfqd->grp_service_tree;
+        unsigned int used_sl;
+
+        used_sl = cfq_cfqq_slice_usage(cfqq);
+
+        /* Can't update vdisktime while group is on service tree */
+        cfq_rb_erase(&cfqg->rb_node, st);
+        cfqg->vdisktime += cfq_scale_slice(used_sl, cfqg);
+        __cfq_group_service_tree_add(st, cfqg);
+
+        /* This group is being expired. Save the context */
+        if (time_after(cfqd->workload_expires, jiffies)) {
+                cfqg->saved_workload_slice = cfqd->workload_expires
+                                                - jiffies;
+                cfqg->saved_workload = cfqd->serving_type;
+                cfqg->saved_serving_prio = cfqd->serving_prio;
+        } else
+                cfqg->saved_workload_slice = 0;
 }
 
 /*
@@ -833,6 +894,7 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
         unsigned long rb_key;
         struct cfq_rb_root *service_tree;
         int left;
+        int new_cfqq = 1;
 
         service_tree = service_tree_for(cfqq->cfqg, cfqq_prio(cfqq),
                                                 cfqq_type(cfqq), cfqd);
@@ -861,6 +923,7 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
         }
 
         if (!RB_EMPTY_NODE(&cfqq->rb_node)) {
+                new_cfqq = 0;
                 /*
                  * same position, nothing more to do
                  */
@@ -902,6 +965,8 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
         rb_link_node(&cfqq->rb_node, parent, p);
         rb_insert_color(&cfqq->rb_node, &service_tree->rb);
         service_tree->count++;
+        if (add_front || !new_cfqq)
+                return;
         cfq_group_service_tree_add(cfqd, cfqq->cfqg);
 }
 
@@ -1218,6 +1283,8 @@ static void __cfq_set_active_queue(struct cfq_data *cfqd,
 {
         if (cfqq) {
                 cfq_log_cfqq(cfqd, cfqq, "set_active");
+                cfqq->slice_start = 0;
+                cfqq->dispatch_start = jiffies;
                 cfqq->slice_end = 0;
                 cfqq->slice_dispatch = 0;
 
@@ -1255,6 +1322,8 @@ __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                 cfq_log_cfqq(cfqd, cfqq, "resid=%ld", cfqq->slice_resid);
         }
 
+        cfq_group_served(cfqd, cfqq->cfqg, cfqq);
+
         if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list))
                 cfq_del_cfqq_rr(cfqd, cfqq);
 
@@ -1263,6 +1332,9 @@ __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
         if (cfqq == cfqd->active_queue)
                 cfqd->active_queue = NULL;
 
+        if (&cfqq->cfqg->rb_node == cfqd->grp_service_tree.active)
+                cfqd->grp_service_tree.active = NULL;
+
         if (cfqd->active_cic) {
                 put_io_context(cfqd->active_cic->ioc);
                 cfqd->active_cic = NULL;
@@ -1747,6 +1819,13 @@ static void cfq_choose_cfqg(struct cfq_data *cfqd)
         struct cfq_group *cfqg = cfq_get_next_cfqg(cfqd);
 
         cfqd->serving_group = cfqg;
+
+        /* Restore the workload type data */
+        if (cfqg->saved_workload_slice) {
+                cfqd->workload_expires = jiffies + cfqg->saved_workload_slice;
+                cfqd->serving_type = cfqg->saved_workload;
+                cfqd->serving_prio = cfqg->saved_serving_prio;
+        }
         choose_service_tree(cfqd, cfqg);
 }