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Understanding DPDK algorithmics
The document discusses algorithms used in the DPDK libraries for fast lookups. It describes the characteristics and usage of the hash, LPM, and ACL libraries. The hash library uses cuckoo hashing for tables like FDB and host tables. The LPM library uses a modified DIR-24-8-BASIC algorithm for IPv4 and IPv6 route tables. The ACL library classifies entries using techniques like scalar, SSE, and AVX2 based on multi-bit tries. Examples of lookups and inserts are provided for each library.
Understanding DPDK algorithmics
- 1. Understanding DPDK algorithmics Fast lookupalgorithms implemented inside DPDK libraries
- 2. HASH library Used inFDB, IPv4 and IPv6 HOST tables
- 3. DPDK Hash librarycharacteristics Algorithm used is a modified Cuckoo hashing Hash size is 32 bytes Optimistic memory access time is 1 Pessimistic memory access time is 2 With random keys, this method allows the user to get around 90% of the table utilization, without having to drop any stored entry or allocate more memory. Big table is divided in many buckets Cuckoo hashing algorithm is used to find another bucket
- 4. Cuckoo hashing collisionresolution x y New value = x, Old value = y h1(x) h2(y) Table 1 Table 2
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- 7. LPM library Used inIPv4 and IPv6 ROUTE tables
- 8. DPDK LPM librarycharacteristics Uses modified DIR-24-8-BASIC algorithm TBL24 contains 224 next hop entries = 16M * 2B = 32MB Number of TBL8 could be up to 215 = 32K * 2B = 64K Next hop value points to next hop id in case of 24-bit or less prefix and to TBL8 table otherwise Route prefixes less than 24 are expanded into multiple entries inside TBL24 Number of prefixes longer than 24 is limited by the number of TBL8
- 9. Lookup algorithm 0 23 24 31 224 entries TBL24 28entries TBL8 TBL8 28 entries Next hop? Next hop table yes no
- 10. LPM lookup example 192.168.1.1 192.168.2.1 192.168.1.2 192.168/16 ... 192.168/16 192.168/16 TBL8 TBL24 192.168/16 192.168/16 192.168/16 ... 192.168/16 Routeentries: 192.168/16 192.168.1/24 192.168.1.1/32 192.168.1/24 192.168.1.1/32 192.168.1/24 192.168.1/24 192.168.1/24 TBL8 192.168.1/24 192.168.1/24 192.168.1/24 ... 192.168.1/24
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- 12. ACL library Used inIPv4 and IPv6 ACL tables
- 13. DPDK ACL librarycharacteristics Classification mechanisms: Scalar SSE AVX2 Based on multi-bit tries (stride = 8 = 256 bits = 4 bytes )
- 14. Multi-bit trie Root node(256 entries) Node2 (256 entries) Node1 (256 entries) Node3 (256 entries)
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- 16. References DPDK Programmer’s Guide CuckooHashing Visualization Jenkins hash function Routing Lookups in Hardware at Memory Access Speeds High Performance Switches and Routers book MULTIBIT TRIES
- 17. My blog Learning NetworkProgramming
Editor's Notes
- #5 If a space is occupied, the new value is inserted. While an old value is moved to the second table using a second hash function. The process is repeated in case if another collision happens until an empty space is found or timeout.