Please sign in to comment.
block: introduce the BFQ I/O scheduler
Add the BFQ-v1-r1 I/O scheduler to 2.6.35. The general structure is borrowed from CFQ, as much of the code. A (bfq_)queue is associated to each task doing I/O on a device, and each time a scheduling decision has to be taken a queue is selected and it is served until it expires. The main differences are: - slices are given in the service domain: tasks are assigned budgets, measured in number of sectors. Once got the disk, a task must however consume its assigned budget within a configurable maximum time (by default, the maximum possible value of the budgets is automaticall computed to comply with this timeout). This allows the desired latency vs "throughput boosting" tradeoff to be set. - Budgets are scheduled according to a variant of WF2Q+, implemented using an augmented rb-tree to take eligibility into account while preserving an O(log N) overall complexity. - BFQ supports full hierarchical scheduling, exporting a cgroups interface. Each node has a full scheduler, so each group can be assigned its own ioprio and an ioprio_class. - If the cgroups interface is used, weights can be explictly assigned, otherwise ioprio values are mapped to weights using the relation weight = IOPRIO_BE_NR - ioprio. - ioprio classes are served in strict priority order, i.e., lower priority queues are not served as long as there are higher priority queues. Among queues in the same classes the bandwidth is distributed in proportion to the weights of each queue. Regarding what has not changed it is worth noting: - the handling of cfq_io_contexts to associate queues to tasks. Much of the code has been reused just renaming it. (There is room for code sharing with CFQ but we wanted to minimize the impact of this patch.) - The handling of async queues. - The handling of idle windows. - The handling of merging. - The heuristics to assert that a task is worth an idle window (with minor modifications to hw_tag/CIC_SEEKY detection). Signed-off-by: Fabio Checconi <email@example.com> Signed-off-by: Paolo Valente <firstname.lastname@example.org> Ported the following commits to bfq: - cfq-iosched: compact io_context radix_tree (80b15c7) - cfq-iosched: remove dead_key from cfq_io_context (bca4b91)
- Loading branch information...
Showing with 5,021 additions and 0 deletions.
Oops, something went wrong.