Branch records are a CPU feature that can be configured to record certain branches that are taken during code execution. This data is particularly interesting for profile guided optimizations. perf has had branch record support for a while but the data collection can be a bit coarse grained. We (Facebook) have seen in experiments that associating metadata with branch records can improve results (after postprocessing). We generally use bpf_probe_read_*() to get metadata out of userspace. That's why bpf support for branch records is useful. Aside from this particular use case, having branch data available to bpf progs can be useful to get stack traces out of userspace applications that omit frame pointers. Changes in v3: - Document filling unused buffer with zero - Formatting fixes - Rebase Changes in v2: - Change to a bpf helper instead of context access - Avoid mentioning Intel specific things Daniel Xu (3): bpf: Add bpf_perf_prog_read_branches() helper tools/bpf: Sync uapi header bpf.h selftests/bpf: add bpf_perf_prog_read_branches() selftest include/uapi/linux/bpf.h | 15 ++- kernel/trace/bpf_trace.c | 31 +++++ tools/include/uapi/linux/bpf.h | 15 ++- .../selftests/bpf/prog_tests/perf_branches.c | 106 ++++++++++++++++++ .../selftests/bpf/progs/test_perf_branches.c | 39 +++++++ 5 files changed, 204 insertions(+), 2 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/perf_branches.c create mode 100644 tools/testing/selftests/bpf/progs/test_perf_branches.c -- 2.21.1
