Documentation/rtla: Document --bpf-action option

Add new option --bpf-action into common_timerlat_options.txt, including
the format in which it takes the BPF program, and a reference to an
example.

Link: https://lore.kernel.org/r/20251126144205.331954-8-tglozar@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>

diff --git a/Documentation/tools/rtla/common_timerlat_options.txt b/Documentation/tools/rtla/common_timerlat_options.txt
index 0cf7eca1f7b650d041349b0493c9c6abd7ef7b34..07a285fcf7cf7f91d2f3bd1a008cb8069029c5f3 100644 (file)
--- a/Documentation/tools/rtla/common_timerlat_options.txt
+++ b/Documentation/tools/rtla/common_timerlat_options.txt
@@ -65,3 +65,21 @@
         Set timerlat to run without workload, waiting for the user to dispatch a per-cpu
         task that waits for a new period on the tracing/osnoise/per_cpu/cpu$ID/timerlat_fd.
         See linux/tools/rtla/example/timerlat_load.py for an example of user-load code.
+
+**--bpf-action** *bpf-program*
+
+        Loads a BPF program from an ELF file and executes it when a latency threshold is exceeded.
+
+        The BPF program must be a valid ELF file loadable with libbpf. The program must contain
+        a function named ``action_handler``, stored in an ELF section with the ``tp_`` prefix.
+        The prefix is used by libbpf to set BPF program type to BPF_PROG_TYPE_TRACEPOINT.
+
+        The program receives a ``struct trace_event_raw_timerlat_sample`` parameter
+        containing timerlat sample data.
+
+        An example is provided in ``tools/tracing/rtla/example/timerlat_bpf_action.c``.
+        This example demonstrates how to create a BPF program that prints latency information using
+        bpf_trace_printk() when a threshold is exceeded.
+
+        **Note**: BPF actions require BPF support to be available. If BPF is not available
+        or disabled, the tool falls back to tracefs mode and BPF actions are not supported.