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[Qemu-devel] [PULL 4/4] trace: fix simple trace "disable" keyword
From: |
Stefan Hajnoczi |
Subject: |
[Qemu-devel] [PULL 4/4] trace: fix simple trace "disable" keyword |
Date: |
Mon, 27 Jan 2014 15:53:06 +0100 |
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 <address@hidden>
---
scripts/tracetool/backend/simple.py | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/scripts/tracetool/backend/simple.py
b/scripts/tracetool/backend/simple.py
index 30faac9..3dde372 100644
--- a/scripts/tracetool/backend/simple.py
+++ b/scripts/tracetool/backend/simple.py
@@ -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,
)
--
1.8.4.2