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trace: fix simple trace "disable" keyword

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The trace-events "disable" keyword turns an event into a nop at
compile-time.  This is important for high-frequency events that can
impact performance.

The "disable" keyword is currently broken in the simple trace backend.
This patch fixes the problem as follows:

Trace events are identified by their TraceEventID number.  When events
are disabled there are two options for assigning TraceEventID numbers:
1. Skip disabled events and don't assign them a number.
2. Assign numbers for all events regardless of the disabled keyword.

The simple trace backend and its binary file format uses approach #1.

The tracetool infrastructure has been using approach #2 for a while.

The result is that the numbers used in simple trace files do not
correspond with TraceEventIDs.  In trace/simple.c we assumed that they
are identical and therefore emitted bogus numbers.

This patch fixes the bug by using TraceEventID for trace_event_id()
while sticking to approach #1 for simple trace file numbers.  This
preserves simple trace file format compatibility.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2014-01-15 11:10:30 +08:00
parent 05735a2a9c
commit 736ec1677f
1 changed files with 2 additions and 1 deletions
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3
scripts/tracetool/backend/simple.py
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@ -56,7 +56,7 @@ def c(events):
out('',
' TraceEvent *eventp = trace_event_id(%(event_id)s);',
' TraceEvent *eventp = trace_event_id(%(event_enum)s);',
' bool _state = trace_event_get_state_dynamic(eventp);',
' if (!_state) {',
' return;',
@ -65,6 +65,7 @@ def c(events):
' if (trace_record_start(&rec, %(event_id)s, %(size_str)s)) {',
' return; /* Trace Buffer Full, Event Dropped ! */',
' }',
event_enum = 'TRACE_' + event.name.upper(),
event_id = num,
size_str = sizestr,
)