Documentation/rtla: Add actions feature

Document both --on-threshold and --on-end, with examples.

Cc: John Kacur <jkacur@redhat.com>
Cc: Luis Goncalves <lgoncalv@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Chang Yin <cyin@redhat.com>
Cc: Costa Shulyupin <costa.shul@redhat.com>
Cc: Crystal Wood <crwood@redhat.com>
Cc: Gabriele Monaco <gmonaco@redhat.com>
Link: https://lore.kernel.org/20250626123405.1496931-10-tglozar@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Documentation/tools/rtla/common_timerlat_options.rst

@@ -55,3 +55,67 @@
         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/sample/timerlat_load.py for an example of user-load code.
+
+**--on-threshold** *action*
+
+        Defines an action to be executed when tracing is stopped on a latency threshold
+        specified by **-i/--irq** or **-T/--thread**.
+
+        Multiple --on-threshold actions may be specified, and they will be executed in
+        the order they are provided. If any action fails, subsequent actions in the list
+        will not be executed.
+
+        Supported actions are:
+
+        - *trace[,file=<filename>]*
+
+          Saves trace output, optionally taking a filename. Alternative to -t/--trace.
+          Note that nlike -t/--trace, specifying this multiple times will result in
+          the trace being saved multiple times.
+
+        - *signal,num=<sig>,pid=<pid>*
+
+          Sends signal to process. "parent" might be specified in place of pid to target
+          the parent process of rtla.
+
+        - *shell,command=<command>*
+
+          Execute shell command.
+
+        - *continue*
+
+          Continue tracing after actions are executed instead of stopping.
+
+        Example:
+
+        $ rtla timerlat -T 20 --on-threshold trace
+        --on-threshold shell,command="grep ipi_send timerlat_trace.txt"
+        --on-threshold signal,num=2,pid=parent
+
+        This will save a trace with the default filename "timerlat_trace.txt", print its
+        lines that contain the text "ipi_send" on standard output, and send signal 2
+        (SIGINT) to the parent process.
+
+        Performance Considerations:
+
+        For time-sensitive actions, it is recommended to run **rtla timerlat** with BPF
+        support and RT priority. Note that due to implementational limitations, actions
+        might be delayed up to one second after tracing is stopped if BPF mode is not
+        available or disabled.
+
+**--on-end** *action*
+
+        Defines an action to be executed at the end of **rtla timerlat** tracing.
+
+        Multiple --on-end actions can be specified, and they will be executed in the order
+        they are provided. If any action fails, subsequent actions in the list will not be
+        executed.
+
+        See the documentation for **--on-threshold** for the list of supported actions, with
+        the exception that *continue* has no effect.
+
+        Example:
+
+        $ rtla timerlat -d 5s --on-end trace
+
+        This runs rtla timerlat with default options and save trace output at the end.