+++ /dev/null
-Linux Trace Toolkit
-
-Mathieu Desnoyers 17-05-2004
-
-
-1. Read Requests Cases Study
-
-The goal of this document is to describe the typical behavior of viewers when
-they request data to a process traceset. After the implementation of three
-viewers, with different needs, the idea of their need for a trace processing API
-is getting clearer. We then describe a new API for process traceset that would
-better suits the needs of those viewers.
-
-They are splitted in two different categories : the first one is the one where
-the viewers select the events they need by specifying a time interval in the
-traceset and the second one is where the viewers specify a start event by its
-position in the traceset and a certain amount of events it needs.
-
-This is a simplified case study : we look at the direct interaction between
-graphical viewers and process traceset, without the main window as a negociator.
-
-Control Flow Viewer
-
-This viewer, consisting in a two dimensions graph, shows the different processes
-as its y axis and the time as x axis. It's clear that it needs to get the events
-by specifying a start time and an end time, constituing a time interval.
-
-
-Detailed Events List
-
-This list has nothing to do with time : it shows the events one by one. It cares
-about the quantity of events, not their time.
-
-It would be simple to get the events one by one if we were reading only one
-tracefile (one cpu), but the way events are read through each trace
-(monothically increasing time) makes it a little bit more difficult to specify
-how to increment event position. We will determine how it could be done simply.
-
-Let's define an event position. It's a pointer to a position into each
-tracefile. It's only meaningful when associated with a context. Comparisons
-between positions are done by looking comparing saved positions for each
-tracefile, until a difference is found.
-
-A viewer could use a start time as a start event. It would specify a number of
-events it needs. As a first call, it could ask for the start time of the
-traceset. Afterward, it can save the position of the context after the last
-event has been delivered in its after traceset function.
-
-Now, let's see how process traceset could handle it. It would seek in the
-traceset, searching the position number.
-(need a new lttv_process_traceset_seek_position)
-
-Then, the viewer could simply call a process traceset middle function
-specifying a number of events to get.
-
-The whole concept of numbering events would be hidden in the order in which the
-process traceset gets the events in a monothically increasing time.
-
-
-
-2. Architecture
-
-API to seek/read traceset will be extended to fully support both start time,
-start position, end time, end position and number of events as possible
-boundaries for reading.
-
-lttv_process_traceset_seek_time
-lttv_process_traceset_seek_position
-
-lttv_process_traceset_middle
-
-It must be modified to end when it encounters the first criterion : number of
-events to read reached, end time reached, end position reached.
-
-lttv_traceset_context_position_save
-
-The position_save saves a position that can be used later to seek back to this
-exact same position, with event granularity. This implies that the
-process_traceset must deliver events with the same timestamp in a deterministic
-manner. This is actually done by using tracefile and trace numbers in the
-context in the comparison function.
-
-
-
-Description of new context API useage
-
-1. seek
-2. begin -> add middle hooks
- -> call begin hooks by id
-3. middle -> call middle hooks by id
-4. end -> call end hooks by id
- -> remove middle hooks
-
-3. Impact on State
-
-From now on, the state computation will be done in the middle hook call, with a
-priority higher than default. We will define this priority as PRIO_STATE,
-defined to 25.
-
-If state has to be computed, lttv_process_traceset_begin has to be called in
-a first time. It adds the state hooks to the context. Then, the state
-seek_closest will have to be used to restore the nearest state, plus a
-process_traceset with no hooks present other than the state hooks will have to
-be called to go from the closest state to the real time seeked.
-
-The lttv_process_traceset_end will only need to be called if no further state
-computation is needed.
-
-
-4. Implementation in tracecontext.c
-
-
-- Type LttvTracesetContextPosition
-
-struct _LttvTraceContextPosition {
- LttEventPosition *tf_pos; /* Position in each trace */
- guint nb_tracefile; /* Number of tracefiles (check) */
-}
-
-struct _LttvTracesetContextPosition {
- LttTraceContextPosition *t_pos; /* Position in each trace */
- guint nb_trace; /* Number of traces (check) */
-}
-
-with interfaces :
-
-lttv_traceset_context_position_save
-(const LttvTracesetContext *context,
- LttvTracesetContextPosition *pos);
-
-
-Dependencies :
-
-- lttv_process_traceset_seek_position(LttvTracesetContext *self,
- const LttvTracesetContextPosition *position);
- - ltt_tracefile_seek_position : already implemented
-
-lttv_process_traceset_seek_position will seek each tracefile to the right
-position. We keep information about number of tracefiles for extra integrity
-checking when reloading the position in the context. It also loads the pqueue.
-
-
-
-- lttv_process_traceset_middle
-We modify lttv_process_traceset_middle so that it takes as arguments :
-(LttvTracesetContext *self,
-LttTime end,
-unsigned nb_events,
-const LttvTracesetContextPosition *end_position)
-
-This new version of process traceset middle will call the event hooks for
-events until the first criterion is fulfilled : either the end time is reached,
-the number of events requested is passed, the end position is reached or the
-last event hook list called returned TRUE. When this function ends, the end
-position can be extracted from the context, the end event is set as described
-below and the number of events read is returned.
-
-The end event is a pointer to the last event the hooks has been called for.
-
-- lttv_process_traceset_seek_time : already implemented
- - now loads the pqueue.
-
-- lttv_process_traceset_begin(LttvTracesetContext *self,
- LttvHooks *before_traceset,
- LttvHooks *before_trace,
- LttvHooks *before_tracefile,
- LttvHooks *event,
- LttvHooksById *event_by_id)
-
-
-- lttv_process_traceset_end(LttvTracesetContext *self,
- LttvHooks *after_traceset,
- LttvHooks *after_trace,
- LttvHooks *after_tracefile,
- LttvHooks *event,
- LttvHooksById *event_by_id)
-
-- lttv_traceset_context_add_hooks and lttv_traceset_context_remove_hooks
-
-These functions now become internal to tracecontext.c
-
-
-
-
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