Make subbuffer size configurable

Signed-off-by: Christopher Wecht <cwecht@mailbox.org>

tracetools_launch/tracetools_launch/action.py

@@ -114,6 +114,7 @@ def __init__(
         context_fields:
             Union[Iterable[SomeSubstitutionsType], Dict[str, Iterable[SomeSubstitutionsType]]]
             = names.DEFAULT_CONTEXT,
+        subbuffer_size: int = 8 * 4096,
         **kwargs,
     ) -> None:
         """
@@ -139,6 +140,7 @@ def __init__(
             if it's a list or a set, the context fields are enabled for both kernel and userspace;
             if it's a dictionary: { domain type string -> context fields list }
                 with the domain type string being either 'kernel' or 'userspace'
+        :param subbuffer_size: the size of the subbuffers (defaults to 8 times the usual page size)
         """
         super().__init__(**kwargs)
         self.__logger = logging.get_logger(__name__)
@@ -157,6 +159,7 @@ def __init__(
             if isinstance(context_fields, dict) \
             else [normalize_to_list_of_substitutions(field) for field in context_fields]
         self.__ld_preload_actions: List[LdPreload] = []
+        self.__subbuffer_size = subbuffer_size
 
     @property
     def session_name(self):
@@ -380,6 +383,7 @@ def _setup(self) -> bool:
             ros_events=self.__events_ust,
             kernel_events=self.__events_kernel,
             context_fields=self.__context_fields,
+            subbuffer_size=self.__subbuffer_size,
         )
         if self.__trace_directory is None:
             return False
@@ -388,6 +392,7 @@ def _setup(self) -> bool:
         self.__logger.debug(f'Kernel events: {self.__events_kernel}')
         self.__logger.debug(f'Context fields: {self.__context_fields}')
         self.__logger.debug(f'LD_PRELOAD: {self.__ld_preload_actions}')
+        self.__logger.debug(f'Subbuffer size: {self.__subbuffer_size}')
         return True
 
     def _destroy(self, event: Event, context: LaunchContext) -> None:
@@ -404,4 +409,5 @@ def __repr__(self):
             f'events_kernel={self.__events_kernel}, '
             f'context_fields={self.__context_fields}, '
             f'ld_preload_actions={self.__ld_preload_actions})'
+            f'subbuffer_size={self.__subbuffer_size})'
         )

tracetools_trace/tracetools_trace/tools/lttng_impl.py

@@ -73,6 +73,7 @@ def setup(
     context_fields: Union[List[str], Set[str], Dict[str, List[str]]] = DEFAULT_CONTEXT,
     channel_name_ust: str = 'ros2',
     channel_name_kernel: str = 'kchan',
+    subbuffer_size : int = 8 * 4096,
 ) -> Optional[str]:
     """
     Set up LTTng session, with events and context.
@@ -91,6 +92,7 @@ def setup(
         if it's a dictionary: { domain type string -> context fields list }
     :param channel_name_ust: the UST channel name
     :param channel_name_kernel: the kernel channel name
+    :param subbuffer_size: the size of the subbuffers (defaults to 8 times the usual page size)
     :return: the full path to the trace directory, or `None` if initialization failed
     """
     # Check if there is a session daemon running
@@ -142,10 +144,9 @@ def setup(
         channel_ust.name = channel_name_ust
         # Discard, do not overwrite
         channel_ust.attr.overwrite = 0
-        # 2 sub-buffers of 8 times the usual page size
         # We use 2 sub-buffers because the number of sub-buffers is pointless in discard mode,
         # and switching between sub-buffers introduces noticeable CPU overhead
-        channel_ust.attr.subbuf_size = 8 * 4096
+        channel_ust.attr.subbuf_size = subbuffer_size
         channel_ust.attr.num_subbuf = 2
         # Ignore switch timer interval and use read timer instead
         channel_ust.attr.switch_timer_interval = 0