Hello netdev, Lockless Token Bucket(LTB) is a high performance traffic control (TC) qdisc kernel module. The idea is to scale bandwidth sharing in data center networks. Such that online latency sensitive applications could be deployed together with big data applications.
Many thanks to the lockless qdisc patch, we achieve this design goal by eliminating all locks from the critical data path. Briefly, We decouple rate limiting and bandwidth sharing, while still maintaining the rate and ceiling semantics introduced by HTB qdisc. The maximum rate limiting is implemented with a three-stages pipeline running at a high frequency. In a more detail, we use socket priority to classify skbs to different ltb classes, then we aggregate skbs from all CPUS into a single queue called the drain queue. We apply token bucket algorithm on the drain queue to perform rate limiting. After that, we fan out the skbs back to the per-CPU fan out queues to continue transmission. The bandwidth sharing is offloaded to a kernel thread, which is outside of the critical data path. It adjusts each TC class’s maximum rate at a much lower frequency. The algorithm we use to do bandwidth sharing is inspired by the idea presented in [1]. Here’s some quick results we get with pktgen over a 10Gbps link. ./samples/pktgen/pktgen_bench_xmit_mode_queue_xmit.sh –i eth0 -t $NUM We ran it four times and calculated the sum of the results. We did this for 5, 10, 20, and 30 threads with both HTB and LTB. We have seen significant performance gain. And we believe there are still rooms for further improvement. HTB: 5: 1365793 1367419 1367896 1365359 10: 1130063 1131307 1130035 1130385 20: 629792 629517 629219 629234 30: 582358 582537 582707 582716 LTB: 5: 3738416 3745033 3743431 3744847 10: 8327665 8327129 8320331 8322122 20: 6972309 6976670 6975789 6967784 30: 7742397 7742951 7738911 7742812 The real workloads also demonstrate that LTB outperforms HTB significantly especially under heavy traffic, and it scales well to 2 * 25 Gbps networks. Hence, we would like to share this work with the Linux community, and sincerely welcome any feedback and comments. Thank you! [1] To, Khoa and Firestone, Daniel and Varghese, George and Padhye, Jitendra, Measurement Based Fair Queuing for Allocating Bandwidth to Virtual Machines. https://dl.acm.org/doi/abs/10.1145/2940147.2940153 -- Xiangning Yu (2): irq_work: Export symbol "irq_work_queue_on" net: sched: Lockless Token Bucket (LTB) qdisc include/uapi/linux/pkt_sched.h | 35 ++ kernel/irq_work.c | 2 +- net/sched/Kconfig | 12 + net/sched/Makefile | 1 + net/sched/sch_ltb.c | 1280 ++++++++++++++++++++++++++++++++++++++++ 5 files changed, 1329 insertions(+), 1 deletion(-)
