Documentation/rtla: Document SIGINT behavior

The behavior of RTLA on receiving SIGINT is currently undocumented.

Describe it in RTLA's common appendix that appears in man pages for all
RTLA tools to avoid confusion.

Suggested-by: Attila Fazekas <afazekas@redhat.com>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20260324123229.152424-1-tglozar@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>

Author: lenticularis39

Documentation/tools/rtla/common_appendix.txt

@@ -1,5 +1,26 @@
 .. SPDX-License-Identifier: GPL-2.0
 
+SIGINT BEHAVIOR
+===============
+
+On the first SIGINT, RTLA exits after collecting all outstanding samples up to
+the point of receiving the signal.
+
+When receiving more than one SIGINT, RTLA discards any outstanding samples, and
+exits while displaying only samples that have already been processed.
+
+If SIGINT is received during RTLA cleanup, RTLA exits immediately via
+the default signal handler.
+
+Note: For the purpose of SIGINT behavior, the expiry of duration specified via
+the -d/--duration option is treated as equivalent to receiving a SIGINT. For
+example, a SIGINT received after duration expired but samples have not been
+processed yet will drop any outstanding samples.
+
+Also note that when using the timerlat tool in BPF mode, samples are processed
+in-kernel; RTLA only copies them out to display them to the user. A second
+SIGINT does not affect in-kernel sample aggregation.
+
 EXIT STATUS
 ===========