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trace: recommend "log" backend for getting started with tracing

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The "simple" backend is actually more complicated to use than the "log"
backend. Update the quickstart documentation to feature the "log"
backend instead of the "simple" backend.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20201216160923.722894-4-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2020-12-16 16:09:23 +00:00
parent e50caf4a5c
commit 7e46d5f317
1 changed files with 18 additions and 17 deletions
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35
docs/devel/tracing.rst
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@ -11,22 +11,22 @@ for debugging, profiling, and observing execution.
Quickstart
==========
1. Build with the 'simple' trace backend::
Enable tracing of ``memory_region_ops_read`` and ``memory_region_ops_write``
events::
./configure --enable-trace-backends=simple
make
$ qemu --trace "memory_region_ops_*" ...
...
719585@1608130130.441188:memory_region_ops_read cpu 0 mr 0x562fdfbb3820 addr 0x3cc value 0x67 size 1
719585@1608130130.441190:memory_region_ops_write cpu 0 mr 0x562fdfbd2f00 addr 0x3d4 value 0x70e size 2
2. Create a file with the events you want to trace::
This output comes from the "log" trace backend that is enabled by default when
``./configure --enable-trace-backends=BACKENDS`` was not explicitly specified.
echo memory_region_ops_read >/tmp/events
More than one trace event pattern can be specified by providing a file
instead::
3. Run the virtual machine to produce a trace file::
qemu --trace events=/tmp/events ... # your normal QEMU invocation
4. Pretty-print the binary trace file::
./scripts/simpletrace.py trace-events-all trace-* # Override * with QEMU <pid>
$ echo "memory_region_ops_*" >/tmp/events
$ qemu --trace events=/tmp/events ...
Trace events
============
@ -195,7 +195,7 @@ script.
The trace backends are chosen at configure time::
./configure --enable-trace-backends=simple
./configure --enable-trace-backends=simple,dtrace
For a list of supported trace backends, try ./configure --help or see below.
If multiple backends are enabled, the trace is sent to them all.
@ -227,10 +227,11 @@ uses DPRINTF().
Simpletrace
-----------
The "simple" backend supports common use cases and comes as part of the QEMU
source tree. It may not be as powerful as platform-specific or third-party
trace backends but it is portable. This is the recommended trace backend
unless you have specific needs for more advanced backends.
The "simple" backend writes binary trace logs to a file from a thread, making
it lower overhead than the "log" backend. A Python API is available for writing
offline trace file analysis scripts. It may not be as powerful as
platform-specific or third-party trace backends but it is portable and has no
special library dependencies.
Monitor commands
~~~~~~~~~~~~~~~~