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1 . x
DPDK-based
userspace TCP/IP stack testing
SHU MA
EBS – KUAFU
ALIBABA CLOUD
2 .Agenda
1 Background
2 Current status
3 Our practice
4 Q&A
3 .Background
Luna
• high performance network framework
• DPDK
• Luna Stack (userspace lightweight TCP/IP stack)
Product
• ESSD (cloud disk)
• hundreds of production clusters
• tens of thousands of machines
Latency
• 1/3 kernel
• nearly as fast as RDMA
https://www.aliyun.com/product/disk
4 .Background
Challenges in developing Luna Stack
• Bug is time-series-related
• hard to reproduce
Test Framework
• hard to troubleshoot
• Large number of corner cases 1. bug reproduction
• hard to fix 2. trouble shooting
• easy to break other cases 3. regression
4. correctness
• Convince upper-layer developers
• correctness
• robustness
5 .Current status
Linux kernel, FreeBSD
• Internal
• Low unit test coverage
• External (LTP)
• 20+ scripts for TCP/IP
Testing approaches
• Unit test（white box）
• need to know code detail, hard to write
• Function test（black box）
• hard to create scenarios with strict time-series
• packetdrill（grey box）
• Google, open source
• USENIX ATC 2013
• 3 new TCP features, 10 kernel bugs
bug fix for Linux kernel
6 .Packetdrill: script
4 statements 0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+0 bind(3, ..., ...) = 0
• packets
+0 listen(3, 1) = 0
• tcpdump-like syntax
• inbound, outbound +0 < S 0:0(0) win 32792 <mss 1460, nop, wscale 7, nop, nop, TS val 0 ecr 0>
• system calls +0 > S. 0:0(0) ack 1 <mss 1460, nop, nop, TS val 0 ecr 0, nop, wscale 7>
• strace-like syntax +0 `netstat -anp | grep 8080 | grep SYN_RCVD` // examine TCP state
• shell commands
+.1 < . 1:1(0) ack 1 win 100
• python scripts
+0 accept(3, ..., ...) = 4
+0 %{ assert tcpi_snd_cwnd = 10 }% // examine TCP_INFO
time model
• relative time +0 write(4, ..., 1000) = 1000 // send 1 packet
• +0, +.1 +0 > . 1:1001(1000) ack 1
• absolute time
+.2 > . 1:1001(1000) ack 1 // RTO retrans, 200ms
• 0.100, 0.100…0.200
+.4 > . 1:1001(1000) ack 1 // RTO retarns, 400ms
100 lines of UT -> 13 lines of script
7 .Packetdrill: pros & cons
Pros
• time-series
• developer-friendly script syntax
• high maintainability
• reusable among different stacks
libluna.so
1. Posix socket API
Cons 2. DPDK send/receive API
• kernel TCP/IP 3. netstat/ss/pollinghang
• TCP_INFO/netstat/ss
• polling related time-series packetdrill
1. dynamically link libluna.so
2. DPDK polling thread
3. dispatch function call
8 .Modified packetdrill
Main thread
• read script line by line
• send/receive packets via DPDK
• dispatch function
• run shell tools
• inspect: netstat, ss
• interfere: pollinghang?time=10
Stack thread
• polling mode
• userspace stack initialization
• call dispatched function
Usage
• ./packetdrill ./test.pkt
• ./packetdrill --userspace_stack --so_filename=libluna.so ./test.pkt
• Compare between Luna TCP and kernel TCP
9 .Modified packetdrill
0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+0 bind(3, ..., ...) = 0 +0 bind(3, ..., ...) = 0
+0 listen(3, 1) = 0 +0 listen(3, 1) = 0
+0 < S 0:0(0) win 32792 <…> +0 < S 0:0(0) win 32792 <…>
+0 > S. 0:0(0) ack 1 <…> +0 > S. 0:0(0) ack 1 <…>
+0 `netstat -anp | grep 8080 | grep SYN_RCVD` +0 `curl http://127.0.0.1:8899/netstat | grep 8080 | grep SYN_RCVD`
+.1 < . 1:1(0) ack 1 win 100
+.1 < . 1:1(0) ack 1 win 100
+0 accept(3, ..., ...) = 4
+0 accept(3, ..., ...) = 4
+0 `curl http://127.0.0.1:8899/ss | grep 8080 |
+0 %{ assert tcpi_snd_cwnd = 10 }%
sed 's/^.*\(cwnd:[0-9]*\).*$/\1/' | grep 10`
+0 write(4, ..., 1000) = 1000
+0 write(4, ..., 1000) = 1000
+0 > . 1:1001(1000) ack 1 +0 > . 1:1001(1000) ack 1
+.2 > . 1:1001(1000) ack 1 +.2 > . 1:1001(1000) ack 1
+.4 > . 1:1001(1000) ack 1 +.4 > . 1:1001(1000) ack 1
script for kernel TCP script for userspace TCP
10 .Experience in Alibaba
75 test cases for Luna TCP
• TCP state transmission
• exceptional packet handling
• congestion control、keep alive、custom features …
• RFC 793, 1122, 3042, 5681, 6582
reproduction
• fix 3 bugs in production
regression
• added to Jenkins
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