[RFC bpf-next v8 0/9] Improve the performance of BTF type lookups with binary search

[Donglin Peng <dolinux.peng@gmail.com>]

From: pengdonglin <pengdonglin@xiaomi.com>

This patch series introduces significant performance improvements (~2855x)
for BTF type lookups by implementing type permutation and binary search
optimizations.

The series addresses the performance limitations of linear search in large
BTFs by:
1. Adding BTF permutation support
2. Using resolve_btfids to sort BTF during the build phase
3. Checking BTF sorting
4. Using binary search when looking up types

Patch #1 introduces an interface for btf__permute in libbpf to relay out BTF.
Patch #2 adds test cases to validate the functionality of btf__permute in base
         and split BTF scenarios.
Patch #3 introduces a new phase in the resolve_btfids tool to sort BTF by name
         in ascending order.
Patches #4-#7 implement the sorting check and binary search.
Patches #8-#9 optimize type lookup performance of two kernel functions.

Here is a simple performance result [1] to find 60,995 named types in vmlinux
BTF:
./vmtest.sh -- ./test_progs -t btf_permute/perf -v

Results:
| Condition          | Lookup Time | Improvement  |
|--------------------|-------------|--------------|
| Unsorted (Linear)  | 27,697.4 ms | Baseline     |
| Sorted (Binary)    |      9.7 ms | 2855x faster |

The binary search implementation reduces lookup time from 27.7 seconds to 9.7
milliseconds, achieving a **2855x** speedup for large-scale type queries.

Changelog:
v8:  
- Remove the type dropping feature of btf__permute (Andrii)
- Refactor the code of btf__permute (Andrii, Eduard)
- Make the self-test code cleaner (Eduard)
- Reconstruct the BTF sorting patch based on Ihor's patch series [2]
- Simplify the sorting logic and place anonymous types before named types
  (Andrii, Eduard)
- Optimize type lookup performance of two kernel functions
- Refactoring the binary search and type lookup logic achieves a 4.2%
  performance gain, reducing the average lookup time (via the perf test
  code in [1] for 60,995 named types in vmlinux BTF) from 10,217 us (v7) to
  9,783 us (v8).

v7:
- Link: https://lore.kernel.org/all/20251119031531.1817099-1-dolinux.peng@gmail.com/
- btf__permute API refinement: Adjusted id_map and id_map_cnt parameter
  usage so that for base BTF, id_map[0] now contains the new id of original
  type id 1 (instead of VOID type id 0), improving logical consistency
- Selftest updates: Modified test cases to align with the API usage changes
- Refactor the code of resolve_btfids

v6:
- Link: https://lore.kernel.org/all/20251117132623.3807094-1-dolinux.peng@gmail.com/
- ID Map-based reimplementation of btf__permute (Andrii)
- Build-time BTF sorting using resolve_btfids (Alexei, Eduard)
- Binary search method refactoring (Andrii)
- Enhanced selftest coverage

v5:
- Link: https://lore.kernel.org/all/20251106131956.1222864-1-dolinux.peng@gmail.com/
- Refactor binary search implementation for improved efficiency
  (Thanks to Andrii and Eduard)
- Extend btf__permute interface with 'ids_sz' parameter to support
  type dropping feature (suggested by Andrii). Plan subsequent reimplementation of
  id_map version for comparative analysis with current sequence interface
- Add comprehensive test coverage for type dropping functionality
- Enhance function comment clarity and accuracy

v4:
- Link: https://lore.kernel.org/all/20251104134033.344807-1-dolinux.peng@gmail.com/
- Abstracted btf_dedup_remap_types logic into a helper function (suggested by Eduard).
- Removed btf_sort.c and implemented sorting separately for libbpf and kernel (suggested by Andrii).
- Added test cases for both base BTF and split BTF scenarios (suggested by Eduard).
- Added validation for name-only sorting of types (suggested by Andrii)
- Refactored btf__permute implementation to reduce complexity (suggested by Andrii)
- Add doc comments for btf__permute (suggested by Andrii)

v3:
- Link: https://lore.kernel.org/all/20251027135423.3098490-1-dolinux.peng@gmail.com/
- Remove sorting logic from libbpf and provide a generic btf__permute() interface (suggested
  by Andrii)
- Omitted the search direction patch to avoid conflicts with base BTF (suggested by Eduard).
- Include btf_sort.c directly in btf.c to reduce function call overhead

v2:
- Link: https://lore.kernel.org/all/20251020093941.548058-1-dolinux.peng@gmail.com/
- Moved sorting to the build phase to reduce overhead (suggested by Alexei).
- Integrated sorting into btf_dedup_compact_and_sort_types (suggested by Eduard).
- Added sorting checks during BTF parsing.
- Consolidated common logic into btf_sort.c for sharing (suggested by Alan).

v1:
- Link: https://lore.kernel.org/all/20251013131537.1927035-1-dolinux.peng@gmail.com/

[1] https://github.com/pengdonglin137/btf_sort_test
[2] https://lore.kernel.org/bpf/20251126012656.3546071-1-ihor.solodrai@linux.dev/

pengdonglin (9):
  libbpf: Add BTF permutation support for type reordering
  selftests/bpf: Add test cases for btf__permute functionality
  tools/resolve_btfids: Support BTF sorting feature
  libbpf: Optimize type lookup with binary search for sorted BTF
  libbpf: Verify BTF Sorting
  btf: Optimize type lookup with binary search
  btf: Verify BTF Sorting
  bpf: Optimize the performance of find_btf_percpu_datasec
  bpf: Optimize the performance of find_bpffs_btf_enums

 include/linux/btf.h                           |   1 +
 kernel/bpf/btf.c                              | 148 +++++++++-
 kernel/bpf/inode.c                            |  42 ++-
 kernel/bpf/verifier.c                         |   7 +-
 tools/bpf/resolve_btfids/main.c               |  68 +++++
 tools/lib/bpf/btf.c                           | 260 ++++++++++++++++--
 tools/lib/bpf/btf.h                           |  36 +++
 tools/lib/bpf/libbpf.map                      |   1 +
 .../selftests/bpf/prog_tests/btf_permute.c    | 228 +++++++++++++++
 9 files changed, 733 insertions(+), 58 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/btf_permute.c

-- 
2.34.1