int nr_active;
unsigned int children_weight;
+ /*
+ * vfraction is the fraction of vdisktime that the tasks in this
+ * cfqg are entitled to. This is determined by compounding the
+ * ratios walking up from this cfqg to the root.
+ *
+ * It is in fixed point w/ CFQ_SERVICE_SHIFT and the sum of all
+ * vfractions on a service tree is approximately 1. The sum may
+ * deviate a bit due to rounding errors and fluctuations caused by
+ * cfqgs entering and leaving the service tree.
+ */
+ unsigned int vfraction;
+
/*
* There are two weights - (internal) weight is the weight of this
* cfqg against the sibling cfqgs. leaf_weight is the wight of
return cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio);
}
-static inline u64 cfq_scale_slice(unsigned long delta, struct cfq_group *cfqg)
+/**
+ * cfqg_scale_charge - scale disk time charge according to cfqg weight
+ * @charge: disk time being charged
+ * @vfraction: vfraction of the cfqg, fixed point w/ CFQ_SERVICE_SHIFT
+ *
+ * Scale @charge according to @vfraction, which is in range (0, 1]. The
+ * scaling is inversely proportional.
+ *
+ * scaled = charge / vfraction
+ *
+ * The result is also in fixed point w/ CFQ_SERVICE_SHIFT.
+ */
+static inline u64 cfqg_scale_charge(unsigned long charge,
+ unsigned int vfraction)
{
- u64 d = delta << CFQ_SERVICE_SHIFT;
+ u64 c = charge << CFQ_SERVICE_SHIFT; /* make it fixed point */
- d = d * CFQ_WEIGHT_DEFAULT;
- do_div(d, cfqg->weight);
- return d;
+ /* charge / vfraction */
+ c <<= CFQ_SERVICE_SHIFT;
+ do_div(c, vfraction);
+ return c;
}
static inline u64 max_vdisktime(u64 min_vdisktime, u64 vdisktime)
static void
cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg)
{
+ unsigned int vfr = 1 << CFQ_SERVICE_SHIFT; /* start with 1 */
struct cfq_group *pos = cfqg;
+ struct cfq_group *parent;
bool propagate;
/* add to the service tree */
st->total_weight += cfqg->weight;
/*
- * Activate @cfqg and propagate activation upwards until we meet an
- * already activated node or reach root.
+ * Activate @cfqg and calculate the portion of vfraction @cfqg is
+ * entitled to. vfraction is calculated by walking the tree
+ * towards the root calculating the fraction it has at each level.
+ * The compounded ratio is how much vfraction @cfqg owns.
+ *
+ * Start with the proportion tasks in this cfqg has against active
+ * children cfqgs - its leaf_weight against children_weight.
*/
propagate = !pos->nr_active++;
pos->children_weight += pos->leaf_weight;
+ vfr = vfr * pos->leaf_weight / pos->children_weight;
- while (propagate) {
- struct cfq_group *parent = cfqg_flat_parent(pos);
-
- if (!parent)
- break;
-
- propagate = !parent->nr_active++;
- parent->children_weight += pos->weight;
+ /*
+ * Compound ->weight walking up the tree. Both activation and
+ * vfraction calculation are done in the same loop. Propagation
+ * stops once an already activated node is met. vfraction
+ * calculation should always continue to the root.
+ */
+ while ((parent = cfqg_flat_parent(pos))) {
+ if (propagate) {
+ propagate = !parent->nr_active++;
+ parent->children_weight += pos->weight;
+ }
+ vfr = vfr * pos->weight / parent->children_weight;
pos = parent;
}
+
+ cfqg->vfraction = max_t(unsigned, vfr, 1);
}
static void
/* @pos has 0 nr_active at this point */
WARN_ON_ONCE(pos->children_weight);
+ pos->vfraction = 0;
if (!parent)
break;
unsigned int used_sl, charge, unaccounted_sl = 0;
int nr_sync = cfqg->nr_cfqq - cfqg_busy_async_queues(cfqd, cfqg)
- cfqg->service_tree_idle.count;
+ unsigned int vfr;
BUG_ON(nr_sync < 0);
used_sl = charge = cfq_cfqq_slice_usage(cfqq, &unaccounted_sl);
else if (!cfq_cfqq_sync(cfqq) && !nr_sync)
charge = cfqq->allocated_slice;
- /* Can't update vdisktime while group is on service tree */
+ /*
+ * Can't update vdisktime while on service tree and cfqg->vfraction
+ * is valid only while on it. Cache vfr, leave the service tree,
+ * update vdisktime and go back on. The re-addition to the tree
+ * will also update the weights as necessary.
+ */
+ vfr = cfqg->vfraction;
cfq_group_service_tree_del(st, cfqg);
- cfqg->vdisktime += cfq_scale_slice(charge, cfqg);
- /* If a new weight was requested, update now, off tree */
+ cfqg->vdisktime += cfqg_scale_charge(charge, vfr);
cfq_group_service_tree_add(st, cfqg);
/* This group is being expired. Save the context */
#endif /* CONFIG_DEBUG_BLK_CGROUP */
static struct cftype cfq_blkcg_files[] = {
+ /* on root, weight is mapped to leaf_weight */
{
.name = "weight_device",
- .read_seq_string = cfqg_print_weight_device,
- .write_string = cfqg_set_weight_device,
+ .flags = CFTYPE_ONLY_ON_ROOT,
+ .read_seq_string = cfqg_print_leaf_weight_device,
+ .write_string = cfqg_set_leaf_weight_device,
.max_write_len = 256,
},
{
.name = "weight",
- .read_seq_string = cfq_print_weight,
- .write_u64 = cfq_set_weight,
+ .flags = CFTYPE_ONLY_ON_ROOT,
+ .read_seq_string = cfq_print_leaf_weight,
+ .write_u64 = cfq_set_leaf_weight,
},
- /* on root, leaf_weight is mapped to weight */
+ /* no such mapping necessary for !roots */
{
- .name = "leaf_weight_device",
- .flags = CFTYPE_ONLY_ON_ROOT,
+ .name = "weight_device",
+ .flags = CFTYPE_NOT_ON_ROOT,
.read_seq_string = cfqg_print_weight_device,
.write_string = cfqg_set_weight_device,
.max_write_len = 256,
},
{
- .name = "leaf_weight",
- .flags = CFTYPE_ONLY_ON_ROOT,
+ .name = "weight",
+ .flags = CFTYPE_NOT_ON_ROOT,
.read_seq_string = cfq_print_weight,
.write_u64 = cfq_set_weight,
},
- /* no such mapping necessary for !roots */
{
.name = "leaf_weight_device",
- .flags = CFTYPE_NOT_ON_ROOT,
.read_seq_string = cfqg_print_leaf_weight_device,
.write_string = cfqg_set_leaf_weight_device,
.max_write_len = 256,
},
{
.name = "leaf_weight",
- .flags = CFTYPE_NOT_ON_ROOT,
.read_seq_string = cfq_print_leaf_weight,
.write_u64 = cfq_set_leaf_weight,
},
projects / linux-2.6-block.git / blobdiff