It's useful to know kprobe's nmissed count. For example with tracing tools, it's important to know when events may have been lost. debugfs currently exposes a control file to get this information, but it is not compatible with probes registered with the perf API. While bpf programs may be able to manually count nhit, there is no way to gather nmissed. In other words, it is currently not possible to this retrieve information about FD-based probes. This patch adds a new field to perf's read_format that lets users query misses. Misses include both misses from the underlying kprobe infrastructure and misses from ringbuffer infrastructure. I studied the code various code paths for perf software events and perf tracepoints and it does not look like anything can "miss" in the same way kprobes can. They can all, however, suffer from ringbuffer misses. It's possible I missed something while reading the code so please let me know if I am mistaken. Daniel Xu (5): perf/core: Add PERF_FORMAT_LOST read_format perf/core: Sync perf_event.h to tools libbpf: Add helpers to extract perf fd from bpf_link libbpf: Set read_format PERF_FORMAT_LOST on kprobe perf fds libbpf: Add selftest for PERF_FORMAT_LOST perf read_format include/linux/trace_events.h | 1 + include/uapi/linux/perf_event.h | 5 ++- kernel/events/core.c | 39 +++++++++++++++++-- kernel/trace/trace_kprobe.c | 8 ++++ tools/include/uapi/linux/perf_event.h | 5 ++- tools/lib/bpf/libbpf.c | 30 ++++++++++++-- tools/lib/bpf/libbpf.h | 13 +++++++ tools/lib/bpf/libbpf.map | 3 ++ .../selftests/bpf/prog_tests/attach_probe.c | 32 ++++++++++++++- 9 files changed, 127 insertions(+), 9 deletions(-) -- 2.21.0
