[v4,bpf-next,0/6] bpf: add percpu stats for bpf_map

Message

Anton Protopopov July 5, 2023, 4:01 p.m. UTC

This series adds a mechanism for maps to populate per-cpu counters on
insertions/deletions. The sum of these counters can be accessed by a new kfunc
from map iterator and tracing programs.

The following patches are present in the series:

  * Patch 1 adds a generic per-cpu counter to struct bpf_map
  * Patch 2 adds a new kfunc to access the sum of per-cpu counters
  * Patch 3 utilizes this mechanism for hash-based maps
  * Patch 4 extends the preloaded map iterator to dump the sum
  * Patch 5 adds a self-test for the change
  * Patch 6 patches map_ptr selftest to check that elem_count was initialized

The reason for adding this functionality in our case (Cilium) is to get signals
about how full some heavy-used maps are and what the actual dynamic profile of
map capacity is. In the case of LRU maps this is impossible to get this
information anyhow else. The original presentation can be found here [1].

  [1] https://lpc.events/event/16/contributions/1368/

v3 -> v4:
* fix selftests:
  * added test code for batch map operations
  * added a test for BPF_MAP_TYPE_HASH_OF_MAPS (Hao)
  * added tests for BPF_MAP_TYPE_LRU* with BPF_F_NO_COMMON_LRU (Hao)
  * map_info was called multiple times unnecessarily (Hao)
  * small fixes + some memory leaks (Hao)
* fixed wrong error path for freeing a non-prealloc map (Hao)
* fixed counters for batch delete operations (Hao)

v2 -> v3:
- split commits to better represent update logic (Alexei)
- remove filter from kfunc to allow all tracing programs (Alexei)
- extend selftests (Alexei)

v1 -> v2:
- make the counters generic part of struct bpf_map (Alexei)
- don't use map_info and /proc/self/fdinfo in favor of a kfunc (Alexei)

Anton Protopopov (6):
  bpf: add percpu stats for bpf_map elements insertions/deletions
  bpf: add a new kfunc to return current bpf_map elements count
  bpf: populate the per-cpu insertions/deletions counters for hashmaps
  bpf: make preloaded map iterators to display map elements count
  selftests/bpf: test map percpu stats
  selftests/bpf: check that ->elem_count is non-zero for the hash map

 include/linux/bpf.h                           |  30 +
 kernel/bpf/hashtab.c                          |  23 +-
 kernel/bpf/map_iter.c                         |  39 +-
 kernel/bpf/preload/iterators/iterators.bpf.c  |   9 +-
 .../iterators/iterators.lskel-little-endian.h | 526 +++++++++---------
 .../bpf/map_tests/map_percpu_stats.c          | 450 +++++++++++++++
 .../selftests/bpf/progs/map_percpu_stats.c    |  24 +
 .../selftests/bpf/progs/map_ptr_kern.c        |   3 +
 8 files changed, 841 insertions(+), 263 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/map_tests/map_percpu_stats.c
 create mode 100644 tools/testing/selftests/bpf/progs/map_percpu_stats.c