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[Qemu-devel] [PATCH v3 07/10] trace-state: always use the "nop" backend
From: |
Lluís |
Subject: |
[Qemu-devel] [PATCH v3 07/10] trace-state: always use the "nop" backend on events with the "disable" keyword |
Date: |
Mon, 02 May 2011 15:12:26 +0200 |
User-agent: |
StGit/0.15 |
Any event with the keyword/property "disable" generates an empty trace event
using the "nop" backend, regardless of the current backend.
Signed-off-by: Lluís Vilanova <address@hidden>
---
docs/tracing.txt | 25 +++++++++++++++----------
scripts/tracetool | 15 ++-------------
2 files changed, 17 insertions(+), 23 deletions(-)
diff --git a/docs/tracing.txt b/docs/tracing.txt
index 85d2880..1c7b69b 100644
--- a/docs/tracing.txt
+++ b/docs/tracing.txt
@@ -12,15 +12,11 @@ for debugging, profiling, and observing execution.
./configure --trace-backend=simple
make
-2. Enable trace events you are interested in:
-
- $EDITOR trace-events # remove "disable" from events you want
-
-3. Run the virtual machine to produce a trace file:
+2. Run the virtual machine to produce a trace file:
qemu ... # your normal QEMU invocation
-4. Pretty-print the binary trace file:
+3. Pretty-print the binary trace file:
./simpletrace.py trace-events trace-*
@@ -103,10 +99,11 @@ portability macros, ensure they are preceded and followed
by double quotes:
4. Name trace events after their function. If there are multiple trace events
in one function, append a unique distinguisher at the end of the name.
-5. Declare trace events with the "disable" property. Some trace events can
- produce a lot of output and users are typically only interested in a subset
- of trace events. Marking trace events disabled by default saves the user
- from having to manually disable noisy trace events.
+5. If specific trace events are going to be called a huge number of times, this
+ might have a noticeable performance impact even when the trace events are
+ programmatically disabled. In this case you should declare the trace event
+ with the "disable" property, which will effectively disable it at compile
+ time (using the "nop" backend).
== Generic interface and monitor commands ==
@@ -155,6 +152,9 @@ The "nop" backend generates empty trace event functions so
that the compiler
can optimize out trace events completely. This is the default and imposes no
performance penalty.
+Note that regardless of the selected trace backend, events with the "disable"
+property will be generated with the "nop" backend.
+
=== Stderr ===
The "stderr" backend sends trace events directly to standard error. This
@@ -163,6 +163,11 @@ effectively turns trace events into debug printfs.
This is the simplest backend and can be used together with existing code that
uses DPRINTF().
+Note that with this backend trace events cannot be programmatically
+enabled/disabled. Thus, in order to trim down the amount of output and the
+performance impact of tracing, you might want to add the "disable" property in
+the "trace-events" file for those events you are not interested in.
+
=== Simpletrace ===
The "simple" backend supports common use cases and comes as part of the QEMU
diff --git a/scripts/tracetool b/scripts/tracetool
index e649a5b..e2cf117 100755
--- a/scripts/tracetool
+++ b/scripts/tracetool
@@ -506,21 +506,10 @@ convert()
# Skip comments and empty lines
test -z "${str%%#*}" && continue
+ echo
# Process the line. The nop backend handles disabled lines.
- disable="0"
if has_property "$str" "disable"; then
- disable="1"
- fi
- echo
- if [ "$disable" = "1" ]; then
- # Pass the disabled state as an arg for the simple
- # or DTrace backends which handle it dynamically.
- # For all other backends, call lineto$1_nop()
- if [ $backend = "simple" -o "$backend" = "dtrace" ]; then
- "$process_line" "$str"
- else
- "lineto$1_nop" "${str##disable }"
- fi
+ "lineto$1_nop" "$str"
else
"$process_line" "$str"
fi
- [Qemu-devel] [RFC][PATCH v3 00/10] trace-state: make the behaviour of "disable" consistent across all backends, Lluís, 2011/05/02
- [Qemu-devel] [PATCH v3 01/10] trace: move backend-specific code into the trace/ directory, Lluís, 2011/05/02
- [Qemu-devel] [PATCH v3 02/10] trace: avoid conditional code compilation during option parsing, Lluís, 2011/05/02
- [Qemu-devel] [PATCH v3 03/10] trace: generalize the "property" concept in the trace-events file, Lluís, 2011/05/02
- [Qemu-devel] [PATCH v3 04/10] trace-state: separate trace event control and query routines from the simple backend, Lluís, 2011/05/02
- [Qemu-devel] [PATCH v3 05/10] trace-state: always compile support for controlling and querying trace event states, Lluís, 2011/05/02
- [Qemu-devel] [PATCH v3 06/10] trace-state: add "-trace events" argument to control initial state, Lluís, 2011/05/02
- [Qemu-devel] [PATCH v3 07/10] trace-state: always use the "nop" backend on events with the "disable" keyword,
Lluís <=
- [Qemu-devel] [PATCH v3 08/10] trace-state: [simple] disable all trace points by default, Lluís, 2011/05/02
- [Qemu-devel] [PATCH v3 09/10] trace-state: [stderr] add support for dynamically enabling/disabling events, Lluís, 2011/05/02
- [Qemu-devel] [PATCH v3 10/10] trace: enable all events, Lluís, 2011/05/02
- Re: [Qemu-devel] [RFC][PATCH v3 00/10] trace-state: make the behaviour of "disable" consistent across all backends, Lluís, 2011/05/03