cfq-iosched: Allow parent cgroup to preempt its child

[karo-tx-linux.git] / block / cfq-iosched.c

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 98569c2f373eca985c5d0bda1e03a6a97aec4f5d..e3c591dd8f19d0b46fe42dc842510f9d220af143 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -632,6 +632,13 @@ static inline struct cfq_group *cfqg_parent(struct cfq_group *cfqg)
        return pblkg ? blkg_to_cfqg(pblkg) : NULL;
 }
 
+static inline bool cfqg_is_descendant(struct cfq_group *cfqg,
+                                     struct cfq_group *ancestor)
+{
+       return cgroup_is_descendant(cfqg_to_blkg(cfqg)->blkcg->css.cgroup,
+                                   cfqg_to_blkg(ancestor)->blkcg->css.cgroup);
+}
+
 static inline void cfqg_get(struct cfq_group *cfqg)
 {
        return blkg_get(cfqg_to_blkg(cfqg));
@@ -758,6 +765,11 @@ static void cfqg_stats_xfer_dead(struct cfq_group *cfqg)
 #else  /* CONFIG_CFQ_GROUP_IOSCHED */
 
 static inline struct cfq_group *cfqg_parent(struct cfq_group *cfqg) { return NULL; }
+static inline bool cfqg_is_descendant(struct cfq_group *cfqg,
+                                     struct cfq_group *ancestor)
+{
+       return true;
+}
 static inline void cfqg_get(struct cfq_group *cfqg) { }
 static inline void cfqg_put(struct cfq_group *cfqg) { }
 
@@ -3953,7 +3965,12 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
        if (rq_is_sync(rq) && !cfq_cfqq_sync(cfqq))
                return true;
 
-       if (new_cfqq->cfqg != cfqq->cfqg)
+       /*
+        * Treat ancestors of current cgroup the same way as current cgroup.
+        * For anybody else we disallow preemption to guarantee service
+        * fairness among cgroups.
+        */
+       if (!cfqg_is_descendant(cfqq->cfqg, new_cfqq->cfqg))
                return false;
 
        if (cfq_slice_used(cfqq))