[PATCH bpf-next v3 0/4] Optimize bpf_csum_diff() and homogenize for all archs

Puranjay Mohan
2024-10-26T12:54:04Z

Changes in v3:
v2: https://lore.kernel.org/all/20241023153922.86909-1-puranjay@kernel.org/
- Fix sparse warning in patch 2

Changes in v2:
v1: https://lore.kernel.org/all/20241021122112.101513-1-puranjay@kernel.org/
- Remove the patch that adds the benchmark as it is not useful enough to be
added to the tree.
- Fixed a sparse warning in patch 1.
- Add reviewed-by and acked-by tags.

NOTE: There are some sparse warning in net/core/filter.c but those are not
worth fixing because bpf helpers take and return u64 values and using them
in csum related functions that take and return __sum16 / __wsum would need
a lot of casts everywhere.

The bpf_csum_diff() helper currently returns different values on different
architectures because it calls csum_partial() that is either implemented by
the architecture like x86_64, arm, etc or uses the generic implementation
in lib/checksum.c like arm64, riscv, etc.

The implementation in lib/checksum.c returns the folded result that is
16-bit long, but the architecture specific implementation can return an
unfolded value that is larger than 16-bits.

The helper uses a per-cpu scratchpad buffer for copying the data and then
computing the csum on this buffer. This can be optimised by utilising some
mathematical properties of csum.

The patch 1 in this series does preparatory work for homogenizing the
helper. patch 2 does the changes to the helper itself. The performance gain
can be seen in the tables below that are generated using the benchmark
built in patch 4 of v1 of this series:

x86-64:
+-------------+------------------+------------------+-------------+
| Buffer Size | Before | After | Improvement |
+-------------+------------------+------------------+-------------+
| 4 | 2.296 ± 0.066M/s | 3.415 ± 0.001M/s | 48.73 % |
| 8 | 2.320 ± 0.003M/s | 3.409 ± 0.003M/s | 46.93 % |
| 16 | 2.315 ± 0.001M/s | 3.414 ± 0.003M/s | 47.47 % |
| 20 | 2.318 ± 0.001M/s | 3.416 ± 0.001M/s | 47.36 % |
| 32 | 2.308 ± 0.003M/s | 3.413 ± 0.003M/s | 47.87 % |
| 40 | 2.300 ± 0.029M/s | 3.413 ± 0.003M/s | 48.39 % |
| 64 | 2.286 ± 0.001M/s | 3.410 ± 0.001M/s | 49.16 % |
| 128 | 2.250 ± 0.001M/s | 3.404 ± 0.001M/s | 51.28 % |
| 256 | 2.173 ± 0.001M/s | 3.383 ± 0.001M/s | 55.68 % |
| 512 | 2.023 ± 0.055M/s | 3.340 ± 0.001M/s | 65.10 % |
+-------------+------------------+------------------+-------------+

ARM64:
+-------------+------------------+------------------+-------------+
| Buffer Size | Before | After | Improvement |
+-------------+------------------+------------------+-------------+
| 4 | 1.397 ± 0.005M/s | 1.493 ± 0.005M/s | 6.87 % |
| 8 | 1.402 ± 0.002M/s | 1.489 ± 0.002M/s | 6.20 % |
| 16 | 1.391 ± 0.001M/s | 1.481 ± 0.001M/s | 6.47 % |
| 20 | 1.379 ± 0.001M/s | 1.477 ± 0.001M/s | 7.10 % |
| 32 | 1.358 ± 0.001M/s | 1.469 ± 0.002M/s | 8.17 % |
| 40 | 1.339 ± 0.001M/s | 1.462 ± 0.002M/s | 9.18 % |
| 64 | 1.302 ± 0.002M/s | 1.449 ± 0.003M/s | 11.29 % |
| 128 | 1.214 ± 0.001M/s | 1.443 ± 0.003M/s | 18.86 % |
| 256 | 1.080 ± 0.001M/s | 1.423 ± 0.001M/s | 31.75 % |
| 512 | 0.887 ± 0.001M/s | 1.411 ± 0.002M/s | 59.07 % |
+-------------+------------------+------------------+-------------+

Patch 3 reverts a hack that was done to make the selftest pass on all
architectures.

Patch 4 adds a selftest for this helper to verify the results produced by
this helper in multiple modes and edge cases.

Puranjay Mohan (4):
net: checksum: move from32to16() to generic header
bpf: bpf_csum_diff: optimize and homogenize for all archs
selftests/bpf: don't mask result of bpf_csum_diff() in test_verifier
selftests/bpf: Add a selftest for bpf_csum_diff()

arch/parisc/lib/checksum.c | 13 +-
include/net/checksum.h | 6 +
lib/checksum.c | 11 +-
net/core/filter.c | 39 +-
.../selftests/bpf/prog_tests/test_csum_diff.c | 408 ++++++++++++++++++
.../selftests/bpf/progs/csum_diff_test.c | 42 ++
.../bpf/progs/verifier_array_access.c | 3 +-
7 files changed, 471 insertions(+), 51 deletions(-)
create mode 100644 tools/testing/selftests/bpf/prog_tests/test_csum_diff.c
create mode 100644 tools/testing/selftests/bpf/progs/csum_diff_test.c

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2.40.1