diff options
| -rw-r--r-- | Documentation/block/cfq-iosched.txt | 58 | ||||
| -rw-r--r-- | Documentation/cgroups/blkio-controller.txt | 35 | ||||
| -rw-r--r-- | block/cfq-iosched.c | 21 |
3 files changed, 88 insertions, 26 deletions
diff --git a/Documentation/block/cfq-iosched.txt b/Documentation/block/cfq-iosched.txt index d89b4fe..a5eb7d1 100644 --- a/Documentation/block/cfq-iosched.txt +++ b/Documentation/block/cfq-iosched.txt @@ -102,6 +102,64 @@ processing of request. Therefore, increasing the value can imporve the performace although this can cause the latency of some I/O to increase due to more number of requests. +CFQ Group scheduling +==================== + +CFQ supports blkio cgroup and has "blkio." prefixed files in each +blkio cgroup directory. It is weight-based and there are four knobs +for configuration - weight[_device] and leaf_weight[_device]. +Internal cgroup nodes (the ones with children) can also have tasks in +them, so the former two configure how much proportion the cgroup as a +whole is entitled to at its parent's level while the latter two +configure how much proportion the tasks in the cgroup have compared to +its direct children. + +Another way to think about it is assuming that each internal node has +an implicit leaf child node which hosts all the tasks whose weight is +configured by leaf_weight[_device]. Let's assume a blkio hierarchy +composed of five cgroups - root, A, B, AA and AB - with the following +weights where the names represent the hierarchy. + + weight leaf_weight + root : 125 125 + A : 500 750 + B : 250 500 + AA : 500 500 + AB : 1000 500 + +root never has a parent making its weight is meaningless. For backward +compatibility, weight is always kept in sync with leaf_weight. B, AA +and AB have no child and thus its tasks have no children cgroup to +compete with. They always get 100% of what the cgroup won at the +parent level. Considering only the weights which matter, the hierarchy +looks like the following. + + root + / | \ + A B leaf + 500 250 125 + / | \ + AA AB leaf + 500 1000 750 + +If all cgroups have active IOs and competing with each other, disk +time will be distributed like the following. + +Distribution below root. The total active weight at this level is +A:500 + B:250 + C:125 = 875. + + root-leaf : 125 / 875 =~ 14% + A : 500 / 875 =~ 57% + B(-leaf) : 250 / 875 =~ 28% + +A has children and further distributes its 57% among the children and +the implicit leaf node. The total active weight at this level is +AA:500 + AB:1000 + A-leaf:750 = 2250. + + A-leaf : ( 750 / 2250) * A =~ 19% + AA(-leaf) : ( 500 / 2250) * A =~ 12% + AB(-leaf) : (1000 / 2250) * A =~ 25% + CFQ IOPS Mode for group scheduling =================================== Basic CFQ design is to provide priority based time slices. Higher priority diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt index b4b1fb3..1b70843 100644 --- a/Documentation/cgroups/blkio-controller.txt +++ b/Documentation/cgroups/blkio-controller.txt @@ -94,13 +94,11 @@ Throttling/Upper Limit policy Hierarchical Cgroups ==================== -- Currently none of the IO control policy supports hierarchical groups. But - cgroup interface does allow creation of hierarchical cgroups and internally - IO policies treat them as flat hierarchy. +- Currently only CFQ supports hierarchical groups. For throttling, + cgroup interface does allow creation of hierarchical cgroups and + internally it treats them as flat hierarchy. - So this patch will allow creation of cgroup hierarchcy but at the backend - everything will be treated as flat. So if somebody created a hierarchy like - as follows. + If somebody created a hierarchy like as follows. root / \ @@ -108,16 +106,20 @@ Hierarchical Cgroups | test3 - CFQ and throttling will practically treat all groups at same level. + CFQ will handle the hierarchy correctly but and throttling will + practically treat all groups at same level. For details on CFQ + hierarchy support, refer to Documentation/block/cfq-iosched.txt. + Throttling will treat the hierarchy as if it looks like the + following. pivot / / \ \ root test1 test2 test3 - Down the line we can implement hierarchical accounting/control support - and also introduce a new cgroup file "use_hierarchy" which will control - whether cgroup hierarchy is viewed as flat or hierarchical by the policy.. - This is how memory controller also has implemented the things. + Nesting cgroups, while allowed, isn't officially supported and blkio + genereates warning when cgroups nest. Once throttling implements + hierarchy support, hierarchy will be supported and the warning will + be removed. Various user visible config options =================================== @@ -172,6 +174,12 @@ Proportional weight policy files dev weight 8:16 300 +- blkio.leaf_weight[_device] + - Equivalents of blkio.weight[_device] for the purpose of + deciding how much weight tasks in the given cgroup has while + competing with the cgroup's child cgroups. For details, + please refer to Documentation/block/cfq-iosched.txt. + - blkio.time - disk time allocated to cgroup per device in milliseconds. First two fields specify the major and minor number of the device and @@ -279,6 +287,11 @@ Proportional weight policy files and minor number of the device and third field specifies the number of times a group was dequeued from a particular device. +- blkio.*_recursive + - Recursive version of various stats. These files show the + same information as their non-recursive counterparts but + include stats from all the descendant cgroups. + Throttling/Upper limit policy files ----------------------------------- - blkio.throttle.read_bps_device diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index ee34282..e8f3106 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -606,20 +606,11 @@ static inline struct cfq_group *blkg_to_cfqg(struct blkcg_gq *blkg) return pd_to_cfqg(blkg_to_pd(blkg, &blkcg_policy_cfq)); } -/* - * Determine the parent cfqg for weight calculation. Currently, cfqg - * scheduling is flat and the root is the parent of everyone else. - */ -static inline struct cfq_group *cfqg_flat_parent(struct cfq_group *cfqg) +static inline struct cfq_group *cfqg_parent(struct cfq_group *cfqg) { - struct blkcg_gq *blkg = cfqg_to_blkg(cfqg); - struct cfq_group *root; - - while (blkg->parent) - blkg = blkg->parent; - root = blkg_to_cfqg(blkg); + struct blkcg_gq *pblkg = cfqg_to_blkg(cfqg)->parent; - return root != cfqg ? root : NULL; + return pblkg ? blkg_to_cfqg(pblkg) : NULL; } static inline void cfqg_get(struct cfq_group *cfqg) @@ -722,7 +713,7 @@ static void cfq_pd_reset_stats(struct blkcg_gq *blkg) #else /* CONFIG_CFQ_GROUP_IOSCHED */ -static inline struct cfq_group *cfqg_flat_parent(struct cfq_group *cfqg) { return NULL; } +static inline struct cfq_group *cfqg_parent(struct cfq_group *cfqg) { return NULL; } static inline void cfqg_get(struct cfq_group *cfqg) { } static inline void cfqg_put(struct cfq_group *cfqg) { } @@ -1290,7 +1281,7 @@ cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg) * stops once an already activated node is met. vfraction * calculation should always continue to the root. */ - while ((parent = cfqg_flat_parent(pos))) { + while ((parent = cfqg_parent(pos))) { if (propagate) { propagate = !parent->nr_active++; parent->children_weight += pos->weight; @@ -1341,7 +1332,7 @@ cfq_group_service_tree_del(struct cfq_rb_root *st, struct cfq_group *cfqg) pos->children_weight -= pos->leaf_weight; while (propagate) { - struct cfq_group *parent = cfqg_flat_parent(pos); + struct cfq_group *parent = cfqg_parent(pos); /* @pos has 0 nr_active at this point */ WARN_ON_ONCE(pos->children_weight); |
