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An Efficient Packet Scheduling Algorithm in Network Processors

An Efficient Packet Scheduling Algorithm in Network Processors. CS260 ---November 2004---. Packet Scheduling in Network Processors. Design Goals: The input load is well balanced among the worker processors Flow order is maintained at the output port.

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An Efficient Packet Scheduling Algorithm in Network Processors

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  1. An Efficient Packet Scheduling Algorithm in Network Processors CS260 ---November 2004---

  2. Packet Scheduling in Network Processors • Design Goals: • The input load is well balanced among the worker processors • Flow order is maintained at the output port

  3. Channel Stripping • N channels • Sender: strip incoming traffic across the N channels • Receiver: combine the traffic into a single stream

  4. Surplus Round Robin

  5. Desired Load Distribution Pattern D-Step: Packet Dispatching P-Step: Packet Processing T-Step: Packet Transmission Dynamic Batch CoScheduling (DBCS)

  6. Problems to Be Addressed • Q: How much workload should be scheduled to each processor? A: Divisible load scheduling & “Processing unit: bytes or packets?” • Q: What if the packets are of variable lengths? A: Packetized DBCS! “Packets  Bytes” • Q: Go for Batches? A: To improve performance. Applicable to a dynamic non-backlogged system. • Q: How much workload should be scheduled in a batch? When to initiate the next batch? • A: Batch Size Determination & Scheduling Time Determination • Q: What if there are multiple flows? • A: Fair scheduling among multiple flows with different reservations?

  7. Load Scheduling Model • Known: Zr,i wi Zs,i N • To determine: aiBTime

  8. Load Distribution in A Single Batch

  9. Optimal Load Fractions in A Single Batch

  10. Load Distribution in Batches

  11. Batch Size Determination • Minimal schedulable batch size: I = C L (L: maximal possible length of a packet) • At least one packet should be dispatched to each processor: mini(aiCL) >= L • Batch size: multiple of I B = m I

  12. Scheduling Time Determination

  13. For a Homogeneous Sytem • zs,i = zr,i = z & wi = w  ai = 1/N

  14. N = 8 Gapr=Gapd=Gapi=0

  15. N = 4 Gapr=Gapd>0 Gapi=0

  16. N = 10 Gapr=Gapd=0 Gapi>0

  17. Best Scheduling Time (N, m, L)

  18. Scalability of the Throughput

  19. Packetized DBCS : Dispatch Decision • If (PacketSize < Balancewhich ) Dispatch; • Else if: • (PacketSize – Balancewhich <= Balancewhich) • (Balancewhich >= PacketSize/2) Dispatch; Else: Do not dispatch. Move on to next processor.

  20. Packetized DBCS

  21. Throughput Verification of P-DBCS

  22. Out of Order Rate Verification of P-DBCS

  23. Throughput Comparison

  24. Out of Order Rate Comparison

  25. Fair Scheduling Among Multiple Flows

  26. Fair Scheduling Among Multiple Flows • Minimal schedulable batch size: I = C L (L: maximal possible length of a packet) • At least one packet should be dispatched to each processor: mini(aiCL) >= L • At least one packet should be selected from each flow: mini(riCL) >= L • Batch size: multiple of I B = m I • Load fraction for each flow: Fi= ri B

  27. Select Decision (F1, F2, … , FM) (F1’, F2’, … , FM’) • If (PacketSize < FBalancewhich ) Select; • Else if: • (PacketSize – FBalancewhich <= FBalancewhich) • (FBalancewhich >= PacketSize/2) Select; Else: Do not select. Move on to next flow.

  28. Fair Scheduling Among Multiple Flows

  29. Fair Scheduling Among Multiple Flows

  30. Throughput of Multiple Flows • Reservations (0.3, 0.3, 0.1, 0.1, 0.1, 0.1)

  31. Out of Order Rate of Multiple Flows

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