blkio: Introduce per cfq group weights and vdisktime calculations

o Bring in the per cfq group weight and how vdisktime is calculated for the
  group. Also bring in the functionality of updating the min_vdisktime of
  the group service tree.

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

2 files changed, 69 insertions, 2 deletions

diff --git a/block/Kconfig.iosched b/block/Kconfig.iosched
index be0280deec29..fa95fa770570 100644
--- a/block/Kconfig.iosched
+++ b/block/Kconfig.iosched
@@ -23,7 +23,6 @@ config IOSCHED_DEADLINE
 
 config IOSCHED_CFQ
         tristate "CFQ I/O scheduler"
-        select BLK_CGROUP
         default y
         ---help---
           The CFQ I/O scheduler tries to distribute bandwidth equally
@@ -33,6 +32,14 @@ config IOSCHED_CFQ
 
           This is the default I/O scheduler.
 
+config CFQ_GROUP_IOSCHED
+        bool "CFQ Group Scheduling support"
+        depends on IOSCHED_CFQ && CGROUPS
+        select BLK_CGROUP
+        default n
+        ---help---
+          Enable group IO scheduling in CFQ.
+
 choice
         prompt "Default I/O scheduler"
         default DEFAULT_CFQ
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index e1f822ac4690..019f28eea9df 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -13,6 +13,7 @@
 #include <linux/rbtree.h>
 #include <linux/ioprio.h>
 #include <linux/blktrace_api.h>
+#include "blk-cgroup.h"
 
 /*
  * tunables
@@ -49,6 +50,7 @@ static const int cfq_hist_divisor = 4;
 
 #define CFQ_SLICE_SCALE         (5)
 #define CFQ_HW_QUEUE_MIN        (5)
+#define CFQ_SERVICE_SHIFT       12
 
 #define RQ_CIC(rq)              \
         ((struct cfq_io_context *) (rq)->elevator_private)
@@ -79,6 +81,7 @@ struct cfq_rb_root {
         struct rb_node *left;
         unsigned count;
         u64 min_vdisktime;
+        struct rb_node *active;
 };
 #define CFQ_RB_ROOT     (struct cfq_rb_root) { RB_ROOT, NULL, 0, 0, }
 
@@ -163,6 +166,7 @@ struct cfq_group {
 
         /* group service_tree key */
         u64 vdisktime;
+        unsigned int weight;
         bool on_st;
 
         /* number of cfqq currently on this group */
@@ -434,6 +438,51 @@ cfq_prio_to_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
         return cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio);
 }
 
+static inline u64 cfq_scale_slice(unsigned long delta, struct cfq_group *cfqg)
+{
+        u64 d = delta << CFQ_SERVICE_SHIFT;
+
+        d = d * BLKIO_WEIGHT_DEFAULT;
+        do_div(d, cfqg->weight);
+        return d;
+}
+
+static inline u64 max_vdisktime(u64 min_vdisktime, u64 vdisktime)
+{
+        s64 delta = (s64)(vdisktime - min_vdisktime);
+        if (delta > 0)
+                min_vdisktime = vdisktime;
+
+        return min_vdisktime;
+}
+
+static inline u64 min_vdisktime(u64 min_vdisktime, u64 vdisktime)
+{
+        s64 delta = (s64)(vdisktime - min_vdisktime);
+        if (delta < 0)
+                min_vdisktime = vdisktime;
+
+        return min_vdisktime;
+}
+
+static void update_min_vdisktime(struct cfq_rb_root *st)
+{
+        u64 vdisktime = st->min_vdisktime;
+        struct cfq_group *cfqg;
+
+        if (st->active) {
+                cfqg = rb_entry_cfqg(st->active);
+                vdisktime = cfqg->vdisktime;
+        }
+
+        if (st->left) {
+                cfqg = rb_entry_cfqg(st->left);
+                vdisktime = min_vdisktime(vdisktime, cfqg->vdisktime);
+        }
+
+        st->min_vdisktime = max_vdisktime(st->min_vdisktime, vdisktime);
+}
+
 /*
  * get averaged number of queues of RT/BE priority.
  * average is updated, with a formula that gives more weight to higher numbers,
@@ -734,8 +783,12 @@ cfq_group_service_tree_del(struct cfq_data *cfqd, struct cfq_group *cfqg)
 {
         struct cfq_rb_root *st = &cfqd->grp_service_tree;
 
+        if (st->active == &cfqg->rb_node)
+                st->active = NULL;
+
         BUG_ON(cfqg->nr_cfqq < 1);
         cfqg->nr_cfqq--;
+
         /* If there are other cfq queues under this group, don't delete it */
         if (cfqg->nr_cfqq)
                 return;
@@ -1654,10 +1707,14 @@ static void choose_service_tree(struct cfq_data *cfqd, struct cfq_group *cfqg)
 static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd)
 {
         struct cfq_rb_root *st = &cfqd->grp_service_tree;
+        struct cfq_group *cfqg;
 
         if (RB_EMPTY_ROOT(&st->rb))
                 return NULL;
-        return cfq_rb_first_group(st);
+        cfqg = cfq_rb_first_group(st);
+        st->active = &cfqg->rb_node;
+        update_min_vdisktime(st);
+        return cfqg;
 }
 
 static void cfq_choose_cfqg(struct cfq_data *cfqd)
@@ -3150,6 +3207,9 @@ static void *cfq_init_queue(struct request_queue *q)
                 *st = CFQ_RB_ROOT;
         RB_CLEAR_NODE(&cfqg->rb_node);
 
+        /* Give preference to root group over other groups */
+        cfqg->weight = 2*BLKIO_WEIGHT_DEFAULT;
+
         /*
          * Not strictly needed (since RB_ROOT just clears the node and we
          * zeroed cfqd on alloc), but better be safe in case someone decides