cfq-iosched: convert cfq_group_slice() to use cfqg->vfraction (41cad6ab) · Commits · 戴 / test

cfq_group_slice() calculates slice by taking a fraction of cfq_target_latency according to the ratio of cfqg->weight against service_tree->total_weight. This currently works only because all cfqgs are treated to be at the same level. To prepare for proper hierarchy support, convert cfq_group_slice() to base the calculation on cfqg->vfraction. As cfqg->vfraction is always a fraction of 1 and represents the fraction allocated to the cfqg with hierarchy considered, the slice can be simply calculated by multiplying cfqg->vfraction to cfq_target_latency (with fixed point shift factored in). As vfraction calculation currently treats all non-root cfqgs as children of the root cfqg, this patch doesn't introduce noticeable behavior difference. Signed-off-by:

Tejun Heo <tj@kernel.org> Acked-by:

Vivek Goyal <vgoyal@redhat.com>

block/cfq-iosched.c

+1 −6

Original line number	Diff line number	Diff line
		@@ -85,7 +85,6 @@ struct cfq_rb_root {
		struct rb_root rb;
		struct rb_node *left;
		unsigned count;
		unsigned total_weight;
		u64 min_vdisktime;
		struct cfq_ttime ttime;
		};
		@@ -979,9 +978,7 @@ static inline unsigned cfq_group_get_avg_queues(struct cfq_data *cfqd,
		static inline unsigned
		cfq_group_slice(struct cfq_data cfqd, struct cfq_group cfqg)
		{
		struct cfq_rb_root *st = &cfqd->grp_service_tree;

		return cfqd->cfq_target_latency * cfqg->weight / st->total_weight;
		return cfqd->cfq_target_latency * cfqg->vfraction >> CFQ_SERVICE_SHIFT;
		}

		static inline unsigned
		@@ -1273,7 +1270,6 @@ cfq_group_service_tree_add(struct cfq_rb_root st, struct cfq_group cfqg)

		cfq_update_group_weight(cfqg);
		__cfq_group_service_tree_add(st, cfqg);
		st->total_weight += cfqg->weight;

		/*
		* Activate @cfqg and calculate the portion of vfraction @cfqg is
		@@ -1360,7 +1356,6 @@ cfq_group_service_tree_del(struct cfq_rb_root st, struct cfq_group cfqg)
		}

		/* remove from the service tree */
		st->total_weight -= cfqg->weight;
		if (!RB_EMPTY_NODE(&cfqg->rb_node))
		cfq_rb_erase(&cfqg->rb_node, st);
		}

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