Overview
Weighted Fair Queuing is a scheduling method that selects or admits work using a concrete priority, fairness, deadline, or capacity rule. It helps expose the policy tradeoff behind queue order, fairness, deadlines, or resource use.
CoreSource checked
Weighted Fair Queuing
Weighted Fair Queuing allocates service according to fairness or proportional-share rules.
Quick Facts
Compact metadata for implementation and discovery.
- Category
- Scheduling
- Difficulty
- Intermediate
- Family
- Scheduling
- Tier
- Core
- Status
- Verified
- Review
- Source Checked
- Sources
- 1
- Formulas
- 1
- Relationships
- 1
- Code example
- Ready
- Visualization
- Ready
- Aliases
- WFQ
Core Concepts
priority ruleresource allocationqueue disciplinetask order
Quick facts
Complexity
Runtime and memory behavior at a glance.
Best
O(n)
Average
O(n log n)
Worst
O(n^2)
Space
O(n)
When to Use
- Use Weighted Fair Queuing when queue order, resource assignment, or deadline policy must be explicit.
- Use it when comparing fairness, latency, throughput, or utilization policies matters.
When Not to Use
- Avoid when the policy would hide starvation, unfairness, or deadline misses.
- Avoid when task durations or priorities are too uncertain for the rule to be meaningful.
What It Does
- Ranks ready work with a scheduling rule
- Updates waiting time, deadlines, or capacity
- Returns an order, assignment, or admission decision
Use Cases
- CPU scheduling
- Network queue management
- Workflow and batch processing
Inputs
- Jobs or requests
- Timing constraints
- Resource limits
Outputs
- Execution order
- Resource assignment
- Timing decision
Key Formulas (1)
Virtual finish time
finishi = max(virtualtime, finishprevious i) + packetlength / weighti
finish_i = max(virtual_time, finish_previous_i) + packet_length / weight_iSchedules packets by a weighted virtual completion time.
Pseudocode
- 1.Collect ready jobs, queues, or tasks
- 2.Compute the method's priority, fairness, or capacity score
- 3.Select the next job or resource assignment
- 4.Update waiting time, capacity, or completion state
- 5.Repeat until all work is scheduled or admitted
Canonical Example
- Input
- jobs = [{id:A, time:3}, {id:B, time:1}], resource = one worker
- Output
- ordered or assigned jobs according to the scheduling rule
- Explanation
- Weighted Fair Queuing computes the priority or capacity rule and chooses the next job from the ready set.
Implementation Notes
- Make tie-breaking deterministic and visible in tests.
- Track waiting time, service time, and resource state separately.
Common Pitfalls
- Forgetting tie-breaking rules makes schedules unstable across runs.
- Ignoring starvation and fairness edge cases can make good averages hide bad tail behavior.
Interactive Mechanism Walkthrough
Graph Frontier & Edge RelaxationShow queued jobs moving onto processors, links, or time slots as the scheduling rule changes priorities.
Step 1 of 5: Collect ready jobs, queues, or tasks
schedulingNotes
Weighted Fair Queuing operates in O(n log n) time and O(n) space within the Scheduling family. Key governing relation: finish_i = max(virtual_time, finish_previous_i) + packet_length / weight_i. Often compared with Round Robin Scheduling and Priority Scheduling.
Sources (1)
What each reference supports for this entry.
Fair Queueing
PaperReference for fair queueing virtual finish times and weighted bandwidth allocation.
Open sourceExplore Next
Good next jumps from the relationship graph, ranked for useful discovery.
Relationships
View full relationship pageConceptual neighborRound Robin Scheduling
Weighted Fair Queuing and Round Robin Scheduling address nearby scheduling problems but make different implementation tradeoffs.
Related Algorithms
Tags
Scheduling