1. Evaluating System Performance in Gigabit Networks King Fahd University of Petroleum and Minerals (KFUPM) INFORMATION AND COMPUTER SCIENCE DEPARTMENT Dr. K. Salah IEEE LCN 2003 Bonn, Germany

2. IEEE LCN 2003 Bonn, Germany KFUPM, ICS Department Evaluating System Performance in Gigabit Networks Agenda Introduction Receive-livelock Phenomenon Contribution Modeling and Analysis Analysis Verification and Validation Numerical Examples Conclusions and Future Work Q&A

3. IEEE LCN 2003 Bonn, Germany KFUPM, ICS Department Evaluating System Performance in Gigabit Networks Introduction High-Speed Network devices are widely deployed Gigabit Ethernet Technology supports 1 Gb/s and 10 Gb/s raw bandwidth Network performance has been shifted to servers and end hosts The high bandwidth increase can negatively impact the OS performance due to the interrupt overhead caused by the incoming gigabit traffic. As interrupt handling has more priority over other processing, this leads to receive-livelock phenomenon

4. IEEE LCN 2003 Bonn, Germany KFUPM, ICS Department Evaluating System Performance in Gigabit Networks Packet Arrival Rate - Slow Protocol Stack Applications Network traffic Host system

5. IEEE LCN 2003 Bonn, Germany KFUPM, ICS Department Evaluating System Performance in Gigabit Networks Packet Arrival Rate - Fast Protocol Stack Applications Host system X Network traffic X

6. IEEE LCN 2003 Bonn, Germany KFUPM, ICS Department Evaluating System Performance in Gigabit Networks Receive-livelock Phenomenon (Source: K. K. Ramakrishnan,1993) Throughput MLFRR Ideal Acceptable Livelock Offered load

7. IEEE LCN 2003 Bonn, Germany KFUPM, ICS Department Evaluating System Performance in Gigabit Networks Our Contribution Many solutions exist for resolving receive livelock and minimizing interrupt overhead No analytical study exists to study the impact of interrupt overhead on system performance and model receive livelock As opposed to simulation and prototyping, analytical study provides a quick and easy way of predicting system behavior and selecting proper design parameters for CPU, OS, and NIC –Buffer size in the NIC –Processing power –Application and Kernel scheduling –Interrupt handling –Using DMA or PIO

8. IEEE LCN 2003 Bonn, Germany KFUPM, ICS Department Evaluating System Performance in Gigabit Networks Modeling and Analysis Analytical models are based on queueing theory and Markov Process –Arrival Rate / Service Rate > 1 –Cannot use Priority Queues with Preemption –Interrupt Overhead is not counted for every Packet Arrival –Use of Mean Effective Service Rate Rate at which packets get processed by the kernel’s protocol with no interrupt disruption Service Rate * (% CPU availability) Three analytical models –An analytical Ideal System where interrupt overhead is ignored –Two analytical models PIO – NICs with no DMA engines –The copying of arrived packets from NIC buffer to host kernel memory is performed by the CPU. –ISR handling is long DMA – NICs with DMA engines –Copying of arrived packets is performed by DMA engines. –ISR handling is very short

9. IEEE LCN 2003 Bonn, Germany KFUPM, ICS Department Evaluating System Performance in Gigabit Networks Analysis Verification and Validation Special cases where verified Verified by Simulation Reported experimental findings show that our analytical models are valid and give a good approximation.

10. IEEE LCN 2003 Bonn, Germany KFUPM, ICS Department Evaluating System Performance in Gigabit Networks Numerical Examples

11. IEEE LCN 2003 Bonn, Germany KFUPM, ICS Department Evaluating System Performance in Gigabit Networks Conclusions and Future Work Analytical models give good approximation Some difference is due to arrival traffic distribution At light load, use of DMA and PIO yields similar system throughput With DMA, receive livelock occurs very late, i.e. at extremely high arrival rate Analysis can be used to study CPU Availability, System Delay, Queue size, etc. As a further study, –Effect of bursty traffic instead of Poisson –Performance of proposed solutions to minimize interrupt overhead Interrupt Coalescing Polling Disable and Enable Interrupts Jumbo Frames

12. IEEE LCN 2003 Bonn, Germany KFUPM, ICS Department Evaluating System Performance in Gigabit Networks Q&A