ping ? On 7/26/2022 9:00 PM, Hou Tao wrote: > Hi, > > The initial motivation for qp-trie map is to reduce memory usage for > string keys special those with large differencies in length as > discussed in [0]. And as a big-endian lexicographical ordered map, it > can also be used for any binary data with fixed or variable length. > > Now the basic functionality of qp-trie is ready, so posting a RFC version > to get more feedback or suggestions about qp-trie. Specially feedback > about the following questions: > > (1) Application scenario for qp-trie > Andrii had proposed to re-implement lpm-trie by using qp-trie. The > advantage would be the speed up of lookup operations due to lower tree > depth of qp-trie. Maybe the performance of update could also be improved > although in cillium there is a big lock during lpm-trie update [1]. Is > there any other use cases for qp-trie ? Specially those cases which need > both ordering and memory efficiency or cases in which jhash() of htab > creates too much collisions and qp-trie lookup performances better than > hash-table lookup as shown below: > > Randomly-generated binary data with variable length (length range=[1, 256] entries=16K) > > htab lookup (1 thread) 5.062 ± 0.004M/s (drops 0.002 ± 0.000M/s mem 8.125 MiB) > htab lookup (2 thread) 10.256 ± 0.017M/s (drops 0.006 ± 0.000M/s mem 8.114 MiB) > htab lookup (4 thread) 20.383 ± 0.006M/s (drops 0.009 ± 0.000M/s mem 8.117 MiB) > htab lookup (8 thread) 40.727 ± 0.093M/s (drops 0.010 ± 0.000M/s mem 8.123 MiB) > htab lookup (16 thread) 81.333 ± 0.311M/s (drops 0.020 ± 0.000M/s mem 8.122 MiB) > > qp-trie lookup (1 thread) 10.161 ± 0.008M/s (drops 0.006 ± 0.000M/s mem 4.847 MiB) > qp-trie lookup (2 thread) 20.287 ± 0.024M/s (drops 0.007 ± 0.000M/s mem 4.828 MiB) > qp-trie lookup (4 thread) 40.784 ± 0.020M/s (drops 0.015 ± 0.000M/s mem 4.071 MiB) > qp-trie lookup (8 thread) 81.165 ± 0.013M/s (drops 0.040 ± 0.000M/s mem 4.045 MiB) > qp-trie lookup (16 thread) 159.955 ± 0.014M/s (drops 0.108 ± 0.000M/s mem 4.495 MiB) > > * non-zero drops is due to duplicated keys in generated keys. > > (2) more fine-grained lock in qp-trie > Now qp-trie is divided into 256 sub-trees by using the first character of > key and one sub-tree is protected one spinlock. From the data below, > although the update/delete speed of qp-trie is slower compare with hash > table, but it scales similar with hash table. So maybe 256-locks is a > good enough solution ? > > Strings in /proc/kallsyms > htab update (1 thread) 2.850 ± 0.129M/s (drops 0.000 ± 0.000M/s mem 33.564 MiB) > htab update (2 thread) 4.363 ± 0.031M/s (drops 0.000 ± 0.000M/s mem 33.563 MiB) > htab update (4 thread) 6.306 ± 0.096M/s (drops 0.000 ± 0.000M/s mem 33.718 MiB) > htab update (8 thread) 6.611 ± 0.026M/s (drops 0.000 ± 0.000M/s mem 33.627 MiB) > htab update (16 thread) 6.390 ± 0.015M/s (drops 0.000 ± 0.000M/s mem 33.564 MiB) > qp-trie update (1 thread) 1.157 ± 0.099M/s (drops 0.000 ± 0.000M/s mem 18.333 MiB) > qp-trie update (2 thread) 1.920 ± 0.062M/s (drops 0.000 ± 0.000M/s mem 18.293 MiB) > qp-trie update (4 thread) 2.630 ± 0.050M/s (drops 0.000 ± 0.000M/s mem 18.472 MiB) > qp-trie update (8 thread) 3.171 ± 0.027M/s (drops 0.000 ± 0.000M/s mem 18.301 MiB) > qp-trie update (16 thread) 3.782 ± 0.036M/s (drops 0.000 ± 0.000M/s mem 19.040 MiB) > > (3) Improve memory efficiency further > When using strings in BTF string section as a data set for qp-trie, the > slab memory usage showed in cgroup memory.stats file is about 11MB for > qp-trie and 15MB for hash table as shown below. However the theoretical > memory usage for qp-trie is ~6.8MB (is ~4.9MB if removing "parent" & "rcu" > fields from qp_trie_branch) and the extra memory usage (about 38% of total > usage) mainly comes from internal fragment in slab (namely 2^n alignment > for allocation) and overhead in kmem-cgroup accounting. We can reduce the > internal fragment by creating separated kmem_cache for qp_trie_branch with > different child nodes, but not sure whether it is worthy or not. > > And in order to prevent allocating a rcu_head for each leaf node, now only > branch node is RCU-freed, so when replacing a leaf node, a new branch node > and a new leaf node will be allocated instead of replacing the old leaf > node and RCU-freed the old leaf node. Also not sure whether or not it is > worthy. > > Strings in BTF string section (entries=115980): > htab lookup (1 thread) 9.889 ± 0.006M/s (drops 0.000 ± 0.000M/s mem 15.069 MiB) > qp-trie lookup (1 thread) 5.132 ± 0.002M/s (drops 0.000 ± 0.000M/s mem 10.721 MiB) > > All files under linux kernel source directory (entries=74359): > htab lookup (1 thread) 8.418 ± 0.077M/s (drops 0.000 ± 0.000M/s mem 14.207 MiB) > qp-trie lookup (1 thread) 4.966 ± 0.003M/s (drops 0.000 ± 0.000M/s mem 9.355 MiB) > > Domain names for Alexa top million web site (entries=1000000): > htab lookup (1 thread) 4.551 ± 0.043M/s (drops 0.000 ± 0.000M/s mem 190.761 MiB) > qp-trie lookup (1 thread) 2.804 ± 0.017M/s (drops 0.000 ± 0.000M/s mem 83.194 MiB) > > Comments and suggestions are always welcome. > > Regards, > Tao > > [0]: https://lore.kernel.org/bpf/CAEf4Bzb7keBS8vXgV5JZzwgNGgMV0X3_guQ_m9JW3X6fJBDpPQ@xxxxxxxxxxxxxx/ > [1]: https://github.com/cilium/cilium/blob/5145e31cd65db3361f6538d5f5f899440b769070/pkg/datapath/prefilter/prefilter.go#L123 > > Hou Tao (3): > bpf: Add support for qp-trie map > selftests/bpf: add a simple test for qp-trie > selftests/bpf: add benchmark for qp-trie map > > include/linux/bpf_types.h | 1 + > include/uapi/linux/bpf.h | 8 + > kernel/bpf/Makefile | 1 + > kernel/bpf/bpf_qp_trie.c | 1064 +++++++++++++++++ > tools/include/uapi/linux/bpf.h | 8 + > tools/testing/selftests/bpf/Makefile | 5 +- > tools/testing/selftests/bpf/bench.c | 10 + > .../selftests/bpf/benchs/bench_qp_trie.c | 499 ++++++++ > .../selftests/bpf/benchs/run_bench_qp_trie.sh | 55 + > .../selftests/bpf/prog_tests/str_key.c | 69 ++ > .../selftests/bpf/progs/qp_trie_bench.c | 218 ++++ > tools/testing/selftests/bpf/progs/str_key.c | 85 ++ > 12 files changed, 2022 insertions(+), 1 deletion(-) > create mode 100644 kernel/bpf/bpf_qp_trie.c > create mode 100644 tools/testing/selftests/bpf/benchs/bench_qp_trie.c > create mode 100755 tools/testing/selftests/bpf/benchs/run_bench_qp_trie.sh > create mode 100644 tools/testing/selftests/bpf/prog_tests/str_key.c > create mode 100644 tools/testing/selftests/bpf/progs/qp_trie_bench.c > create mode 100644 tools/testing/selftests/bpf/progs/str_key.c >
