1. Alex Shpiner, Eitan Zahavi, Ori Rottenstreich April 2014 The Buffer - Bandwidth Tradeoff in Lossless Networks

2. © 2014 Mellanox Technologies 2 - Mellanox Technologies- Background: Network Incast Congestion Source: http://theithollow.com/2013/05/flow-control-explained/ 100% 300%

3. © 2014 Mellanox Technologies 3 - Mellanox Technologies- Background: Pause Frame Flow Control Source: http://theithollow.com/2013/05/flow-control-explained/ Buffer

4. © 2014 Mellanox Technologies 4 - Mellanox Technologies- Background: Incast with Pause Frame Flow Control Source: http://theithollow.com/2013/05/flow-control-explained/ 33% 100%

5. © 2014 Mellanox Technologies 5 - Mellanox Technologies- Background: Congestion Spreading Problem Source: http://theithollow.com/2013/05/flow-control-explained/ This flow is also paused, since the pause control does not distinguish between flows. Effective link bandwidth= Link bandwidth * %unpaused Trade-off 33% instead of 66%

6. © 2014 Mellanox Technologies 6 - Mellanox Technologies- Buffer-bandwidth Tradeoff Effective bandwidth = Link bandwidth * %unpaused

7. © 2014 Mellanox Technologies 7 - Mellanox Technologies- Evaluation Flow 1). Assume network with links of bandwidth C and buffers of size B 2). Define the most challenging workload the network can handle without congestion spreading 3). Increase links bandwidth by α and reduce buffer size by β 4). Evaluate the relation between α and β that able to handle the workload from step 2. Transmit the workload at the same rate, while keeping the same effective link bandwidth

8. © 2014 Mellanox Technologies 8 - Mellanox Technologies- Network Model The most challenging workload:

9. © 2014 Mellanox Technologies 9 - Mellanox Technologies- Determining the Workload Parameters Arrival rate Queue size N senders

10. © 2014 Mellanox Technologies 10 - Mellanox Technologies- Effect of Buffer Size Reduction with Link Acceleration Arriving traffic Input Queue Size Input Queue Size

11. © 2014 Mellanox Technologies 11 - Mellanox Technologies- Effect of Buffer Size Reduction with Link Acceleration– cont.

12. © 2014 Mellanox Technologies 12 - Mellanox Technologies- Effect of Buffer Size Reduction with Link Acceleration– cont.

13. © 2014 Mellanox Technologies 13 - Mellanox Technologies- Asymptotic Analysis α N By increasing link bandwidth by X% the buffer saving is at least X% for any incast load!

14. © 2014 Mellanox Technologies 14 - Mellanox Technologies- Multiple Incast Cascade Analysis Last rank defines the workload parameters: Rank n, α>1, β<1: Rank 1 Rank 2 Rank n

15. © 2014 Mellanox Technologies 15 - Mellanox Technologies- Conclusions

16. © 2014 Mellanox Technologies 16 - Mellanox Technologies- Thank You