| Message ID | 20220620235344.569325-1-eddyz87@gmail.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | bpf_loop inlining | expand |
Hello: This series was applied to bpf/bpf-next.git (master) by Alexei Starovoitov <ast@kernel.org>: On Tue, 21 Jun 2022 02:53:39 +0300 you wrote: > Hi Everyone, > > This is the next iteration of the patch. It includes changes suggested > by Song, Joanne and Alexei. Please find updated intro message and > change log below. > > This patch implements inlining of calls to bpf_loop helper function > when bpf_loop's callback is statically known. E.g. the rewrite does > the following transformation during BPF program processing: > > [...] Here is the summary with links: - [bpf-next,v8,1/5] selftests/bpf: specify expected instructions in test_verifier tests https://git.kernel.org/bpf/bpf-next/c/933ff53191eb - [bpf-next,v8,2/5] selftests/bpf: allow BTF specs and func infos in test_verifier tests https://git.kernel.org/bpf/bpf-next/c/7a42008ca5c7 - [bpf-next,v8,3/5] bpf: Inline calls to bpf_loop when callback is known https://git.kernel.org/bpf/bpf-next/c/1ade23711971 - [bpf-next,v8,4/5] selftests/bpf: BPF test_verifier selftests for bpf_loop inlining https://git.kernel.org/bpf/bpf-next/c/f8acfdd04410 - [bpf-next,v8,5/5] selftests/bpf: BPF test_prog selftests for bpf_loop inlining https://git.kernel.org/bpf/bpf-next/c/0e1bf9ed2000 You are awesome, thank you!
Hi Everyone, This is the next iteration of the patch. It includes changes suggested by Song, Joanne and Alexei. Please find updated intro message and change log below. This patch implements inlining of calls to bpf_loop helper function when bpf_loop's callback is statically known. E.g. the rewrite does the following transformation during BPF program processing: bpf_loop(10, foo, NULL, 0); -> for (int i = 0; i < 10; ++i) foo(i, NULL); The transformation leads to measurable latency change for simple loops. Measurements using `benchs/run_bench_bpf_loop.sh` inside QEMU / KVM on i7-4710HQ CPU show a drop in latency from 14 ns/op to 2 ns/op. The change is split in five parts: * Update to test_verifier.c to specify expected and unexpected instruction sequences. This allows to check BPF program rewrites applied by e.g. do_mix_fixups function. * Update to test_verifier.c to specify BTF function infos and types per test case. This is necessary for tests that load sub-program addresses to a variable because of the checks applied by check_ld_imm function. * The update to verifier.c that tracks state of the parameters for each bpf_loop call in a program and decides whether it could be replaced by a loop. * A set of test cases for `test_verifier` that use capabilities added by the first two patches to verify instructions produced by inlining logic. * Two test cases for `test_prog` to check that possible corner cases behave as expected. Additional details are available in commit messages for each patch. Changes since v7: - Call to `mark_chain_precision` is added in `loop_flag_is_zero` to avoid potential issues with state pruning and precision tracking. - `flags non-zero` test_verifier test case is updated to have two execution paths reaching `bpf_loop` call, one with flags = 0, another with flags = 1. Potentially this test case should be able to show that call to `mark_chain_precision` is necessary in `loop_flag_is_zero` but not at the moment. Please refer to discussion for [PATCH bpf-next v7 3/5] for additional details. - `stack_depth_extra` computation is updated to guarantee that R6, R7 and R8 offsets are always aligned on 8 byte boundary. - `stack locations for loop vars` test_verifier test case updated to show that R6, R7, R8 offsets are indeed aligned when function stack depth is not a multiple of 8. - I removed Song Liu's ACK from commit message for [PATCH bpf-next v8 4/5] because I updated the patch. (Please let me know if I had to keep the ACK tag). Changes since v6: - Return value of the `optimize_bpf_loop` function is no longer ignored. This is necessary to properly propagate -ENOMEM error. Changes since v5: - Added function `loop_flag_is_zero` to skip a few checks in `update_loop_inline_state` when loop instruction is not fit for inline. Changes since v4: - Added missing `static` modifier for `update_loop_inline_state` and `inline_bpf_loop` functions. - `update_loop_inline_state` updated for better readability. - Fields `initialized` and `fit_for_inline` of `struct bpf_loop_inline_state` are changed back from `bool` to bitfields. - Acks from Song Liu added to comments for patches 1/5, 2/5, 4/5, 5/5. Changes since v3: - Function `adjust_stack_depth_for_loop_inlining` is replaced by function `optimize_bpf_loop`. Function `optimize_bpf_loop` is responsible for both stack depth adjustment and call instruction replacement. - Changes in `do_misc_fixups` are reverted. - Changes in `adjust_subprog_starts_after_remove` are reverted and function `adjust_loop_inline_subprogno` is removed. This is possible because call to `optimize_bpf_loop` is placed before the dead code removal in `opt_remove_dead_code` (in contrast to the position of `do_misc_fixups` where inlining was done in v3). - Field `bpf_insn_aux_data.loop_inline_state` is now a part of anonymous union at the start of the `bpf_insn_aux_data`. - Data structure `bpf_loop_inline_state` is simplified to use single flag field `fit_for_inline` instead of separate fields `flags_is_zero` & `callback_is_constant`. - Macro definition `BPF_MAX_LOOPS` is moved from `include/linux/bpf_verifier.h` to `include/linux/bpf.h` to avoid include of `include/linux/bpf_verifier.h` in `bpf_iter.c`. - `inline_bpf_loop` changed back to use array initialization and hard coded offsets as in v2. - Style / formatting updates. Changes since v2: - fix for `stack_check` test case in `test_progs-no_alu32`, all tests are passing now; - v2 3/3 patch is split in three parts: - kernel changes - test_verifier changes - test_prog changes - updated `inline_bpf_loop` in `verifier.c` to calculate each offset used in instructions to avoid "magic" numbers; - removed newline handling logic in `fail_log` branch of `do_single_test` in `test_verifier.c` to simplify the patch set; - styling fixes suggested in review for v2 of this patch set. Changes since v1: - allow to use SKIP_INSNS in instruction pattern specification in test_verifier tests; - fix for a bug in spill offset assignement for loop vars when bpf_loop is located in a non-main function. Eduard Zingerman (5): selftests/bpf: specify expected instructions in test_verifier tests selftests/bpf: allow BTF specs and func infos in test_verifier tests bpf: Inline calls to bpf_loop when callback is known selftests/bpf: BPF test_verifier selftests for bpf_loop inlining selftests/bpf: BPF test_prog selftests for bpf_loop inlining include/linux/bpf.h | 3 + include/linux/bpf_verifier.h | 12 + kernel/bpf/bpf_iter.c | 9 +- kernel/bpf/verifier.c | 180 +++++++++- .../selftests/bpf/prog_tests/bpf_loop.c | 62 ++++ tools/testing/selftests/bpf/prog_tests/btf.c | 1 - tools/testing/selftests/bpf/progs/bpf_loop.c | 114 ++++++ tools/testing/selftests/bpf/test_btf.h | 2 + tools/testing/selftests/bpf/test_verifier.c | 328 +++++++++++++++++- .../selftests/bpf/verifier/bpf_loop_inline.c | 252 ++++++++++++++ 10 files changed, 936 insertions(+), 27 deletions(-) create mode 100644 tools/testing/selftests/bpf/verifier/bpf_loop_inline.c