dce26c7d56
Convert README.trace to reStructured text and move it to develop/trace.rst. Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de> Reviewed-by: Simon Glass <sjg@chromium.org>
356 lines
10 KiB
ReStructuredText
356 lines
10 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+
|
|
.. Copyright (c) 2013 The Chromium OS Authors.
|
|
|
|
Tracing in U-Boot
|
|
=================
|
|
|
|
U-Boot supports a simple tracing feature which allows a record of excecution
|
|
to be collected and sent to a host machine for analysis. At present the
|
|
main use for this is to profile boot time.
|
|
|
|
|
|
Overview
|
|
--------
|
|
|
|
The trace feature uses GCC's instrument-functions feature to trace all
|
|
function entry/exit points. These are then recorded in a memory buffer.
|
|
The memory buffer can be saved to the host over a network link using
|
|
tftpput or by writing to an attached memory device such as MMC.
|
|
|
|
On the host, the file is first converted with a tool called 'proftool',
|
|
which extracts useful information from it. The resulting trace output
|
|
resembles that emitted by Linux's ftrace feature, so can be visually
|
|
displayed by pytimechart.
|
|
|
|
|
|
Quick-start using Sandbox
|
|
-------------------------
|
|
|
|
Sandbox is a build of U-Boot that can run under Linux so it is a convenient
|
|
way of trying out tracing before you use it on your actual board. To do
|
|
this, follow these steps:
|
|
|
|
Add the following to include/configs/sandbox.h (if not already there)
|
|
|
|
.. code-block:: c
|
|
|
|
#define CONFIG_TRACE
|
|
#define CONFIG_CMD_TRACE
|
|
#define CONFIG_TRACE_BUFFER_SIZE (16 << 20)
|
|
#define CONFIG_TRACE_EARLY_SIZE (8 << 20)
|
|
#define CONFIG_TRACE_EARLY
|
|
#define CONFIG_TRACE_EARLY_ADDR 0x00100000
|
|
|
|
Build sandbox U-Boot with tracing enabled:
|
|
|
|
.. code-block:: console
|
|
|
|
$ make FTRACE=1 O=sandbox sandbox_config
|
|
$ make FTRACE=1 O=sandbox
|
|
|
|
Run sandbox, wait for a bit of trace information to appear, and then capture
|
|
a trace:
|
|
|
|
.. code-block:: console
|
|
|
|
$ ./sandbox/u-boot
|
|
|
|
U-Boot 2013.04-rc2-00100-ga72fcef (Apr 17 2013 - 19:25:24)
|
|
|
|
DRAM: 128 MiB
|
|
trace: enabled
|
|
Using default environment
|
|
|
|
In: serial
|
|
Out: serial
|
|
Err: serial
|
|
=>trace stats
|
|
671,406 function sites
|
|
69,712 function calls
|
|
0 untracked function calls
|
|
73,373 traced function calls
|
|
16 maximum observed call depth
|
|
15 call depth limit
|
|
66,491 calls not traced due to depth
|
|
=>trace stats
|
|
671,406 function sites
|
|
1,279,450 function calls
|
|
0 untracked function calls
|
|
950,490 traced function calls (333217 dropped due to overflow)
|
|
16 maximum observed call depth
|
|
15 call depth limit
|
|
1,275,767 calls not traced due to depth
|
|
=>trace calls 0 e00000
|
|
Call list dumped to 00000000, size 0xae0a40
|
|
=>print
|
|
baudrate=115200
|
|
profbase=0
|
|
profoffset=ae0a40
|
|
profsize=e00000
|
|
stderr=serial
|
|
stdin=serial
|
|
stdout=serial
|
|
|
|
Environment size: 117/8188 bytes
|
|
=>host save host 0 trace 0 ${profoffset}
|
|
11405888 bytes written in 10 ms (1.1 GiB/s)
|
|
=>reset
|
|
|
|
|
|
Then run proftool to convert the trace information to ftrace format
|
|
|
|
.. code-block:: console
|
|
|
|
$ ./sandbox/tools/proftool -m sandbox/System.map -p trace dump-ftrace >trace.txt
|
|
|
|
Finally run pytimechart to display it
|
|
|
|
.. code-block:: console
|
|
|
|
$ pytimechart trace.txt
|
|
|
|
Using this tool you can zoom and pan across the trace, with the function
|
|
calls on the left and little marks representing the start and end of each
|
|
function.
|
|
|
|
|
|
CONFIG Options
|
|
--------------
|
|
|
|
CONFIG_TRACE
|
|
Enables the trace feature in U-Boot.
|
|
|
|
CONFIG_CMD_TRACE
|
|
Enables the trace command.
|
|
|
|
CONFIG_TRACE_BUFFER_SIZE
|
|
Size of trace buffer to allocate for U-Boot. This buffer is
|
|
used after relocation, as a place to put function tracing
|
|
information. The address of the buffer is determined by
|
|
the relocation code.
|
|
|
|
CONFIG_TRACE_EARLY
|
|
Define this to start tracing early, before relocation.
|
|
|
|
CONFIG_TRACE_EARLY_SIZE
|
|
Size of 'early' trace buffer. Before U-Boot has relocated
|
|
it doesn't have a proper trace buffer. On many boards
|
|
you can define an area of memory to use for the trace
|
|
buffer until the 'real' trace buffer is available after
|
|
relocation. The contents of this buffer are then copied to
|
|
the real buffer.
|
|
|
|
CONFIG_TRACE_EARLY_ADDR
|
|
Address of early trace buffer
|
|
|
|
|
|
Building U-Boot with Tracing Enabled
|
|
------------------------------------
|
|
|
|
Pass 'FTRACE=1' to the U-Boot Makefile to actually instrument the code.
|
|
This is kept as a separate option so that it is easy to enable/disable
|
|
instrumenting from the command line instead of having to change board
|
|
config files.
|
|
|
|
|
|
Collecting Trace Data
|
|
---------------------
|
|
|
|
When you run U-Boot on your board it will collect trace data up to the
|
|
limit of the trace buffer size you have specified. Once that is exhausted
|
|
no more data will be collected.
|
|
|
|
Collecting trace data has an affect on execution time/performance. You
|
|
will notice this particularly with trvial functions - the overhead of
|
|
recording their execution may even exceed their normal execution time.
|
|
In practice this doesn't matter much so long as you are aware of the
|
|
effect. Once you have done your optimisations, turn off tracing before
|
|
doing end-to-end timing.
|
|
|
|
The best time to start tracing is right at the beginning of U-Boot. The
|
|
best time to stop tracing is right at the end. In practice it is hard
|
|
to achieve these ideals.
|
|
|
|
This implementation enables tracing early in board_init_f(). This means
|
|
that it captures most of the board init process, missing only the
|
|
early architecture-specific init. However, it also misses the entire
|
|
SPL stage if there is one.
|
|
|
|
U-Boot typically ends with a 'bootm' command which loads and runs an
|
|
OS. There is useful trace data in the execution of that bootm
|
|
command. Therefore this implementation provides a way to collect trace
|
|
data after bootm has finished processing, but just before it jumps to
|
|
the OS. In practical terms, U-Boot runs the 'fakegocmd' environment
|
|
variable at this point. This variable should have a short script which
|
|
collects the trace data and writes it somewhere.
|
|
|
|
Trace data collection relies on a microsecond timer, accesed through
|
|
timer_get_us(). So the first think you should do is make sure that
|
|
this produces sensible results for your board. Suitable sources for
|
|
this timer include high resolution timers, PWMs or profile timers if
|
|
available. Most modern SOCs have a suitable timer for this. Make sure
|
|
that you mark this timer (and anything it calls) with
|
|
__attribute__((no_instrument_function)) so that the trace library can
|
|
use it without causing an infinite loop.
|
|
|
|
|
|
Commands
|
|
--------
|
|
|
|
The trace command has variable sub-commands:
|
|
|
|
stats
|
|
Display tracing statistics
|
|
|
|
pause
|
|
Pause tracing
|
|
|
|
resume
|
|
Resume tracing
|
|
|
|
funclist [<addr> <size>]
|
|
Dump a list of functions into the buffer
|
|
|
|
calls [<addr> <size>]
|
|
Dump function call trace into buffer
|
|
|
|
If the address and size are not given, these are obtained from environment
|
|
variables (see below). In any case the environment variables are updated
|
|
after the command runs.
|
|
|
|
|
|
Environment Variables
|
|
---------------------
|
|
|
|
The following are used:
|
|
|
|
profbase
|
|
Base address of trace output buffer
|
|
|
|
profoffset
|
|
Offset of first unwritten byte in trace output buffer
|
|
|
|
profsize
|
|
Size of trace output buffer
|
|
|
|
All of these are set by the 'trace calls' command.
|
|
|
|
These variables keep track of the amount of data written to the trace
|
|
output buffer by the 'trace' command. The trace commands which write data
|
|
to the output buffer can use these to specify the buffer to write to, and
|
|
update profoffset each time. This allows successive commands to append data
|
|
to the same buffer, for example::
|
|
|
|
=> trace funclist 10000 e00000
|
|
=> trace calls
|
|
|
|
(the latter command appends more data to the buffer).
|
|
|
|
|
|
fakegocmd
|
|
Specifies commands to run just before booting the OS. This
|
|
is a useful time to write the trace data to the host for
|
|
processing.
|
|
|
|
|
|
Writing Out Trace Data
|
|
----------------------
|
|
|
|
Once the trace data is in an output buffer in memory there are various ways
|
|
to transmit it to the host. Notably you can use tftput to send the data
|
|
over a network link::
|
|
|
|
fakegocmd=trace pause; usb start; set autoload n; bootp;
|
|
trace calls 10000000 1000000;
|
|
tftpput ${profbase} ${profoffset} 192.168.1.4:/tftpboot/calls
|
|
|
|
This starts up USB (to talk to an attached USB Ethernet dongle), writes
|
|
a trace log to address 10000000 and sends it to a host machine using
|
|
TFTP. After this, U-Boot will boot the OS normally, albeit a little
|
|
later.
|
|
|
|
|
|
Converting Trace Output Data
|
|
----------------------------
|
|
|
|
The trace output data is kept in a binary format which is not documented
|
|
here. To convert it into something useful, you can use proftool.
|
|
|
|
This tool must be given the U-Boot map file and the trace data received
|
|
from running that U-Boot. It produces a text output file.
|
|
|
|
Options
|
|
|
|
-m <map_file>
|
|
Specify U-Boot map file
|
|
|
|
-p <trace_file>
|
|
Specifiy profile/trace file
|
|
|
|
Commands:
|
|
|
|
dump-ftrace
|
|
Write a text dump of the file in Linux ftrace format to stdout
|
|
|
|
|
|
Viewing the Trace Data
|
|
----------------------
|
|
|
|
You can use pytimechart for this (sudo apt-get pytimechart might work on
|
|
your Debian-style machine, and use your favourite search engine to obtain
|
|
documentation). It expects the file to have a .txt extension. The program
|
|
has terse user interface but is very convenient for viewing U-Boot
|
|
profile information.
|
|
|
|
|
|
Workflow Suggestions
|
|
--------------------
|
|
|
|
The following suggestions may be helpful if you are trying to reduce boot
|
|
time:
|
|
|
|
1. Enable CONFIG_BOOTSTAGE and CONFIG_BOOTSTAGE_REPORT. This should get
|
|
you are helpful overall snapshot of the boot time.
|
|
|
|
2. Build U-Boot with tracing and run it. Note the difference in boot time
|
|
(it is common for tracing to add 10% to the time)
|
|
|
|
3. Collect the trace information as descibed above. Use this to find where
|
|
all the time is being spent.
|
|
|
|
4. Take a look at that code and see if you can optimise it. Perhaps it is
|
|
possible to speed up the initialisation of a device, or remove an unused
|
|
feature.
|
|
|
|
5. Rebuild, run and collect again. Compare your results.
|
|
|
|
6. Keep going until you run out of steam, or your boot is fast enough.
|
|
|
|
|
|
Configuring Trace
|
|
-----------------
|
|
|
|
There are a few parameters in the code that you may want to consider.
|
|
There is a function call depth limit (set to 15 by default). When the
|
|
stack depth goes above this then no tracing information is recorded.
|
|
The maximum depth reached is recorded and displayed by the 'trace stats'
|
|
command.
|
|
|
|
|
|
Future Work
|
|
-----------
|
|
|
|
Tracing could be a little tidier in some areas, for example providing
|
|
run-time configuration options for trace.
|
|
|
|
Some other features that might be useful:
|
|
|
|
- Trace filter to select which functions are recorded
|
|
- Sample-based profiling using a timer interrupt
|
|
- Better control over trace depth
|
|
- Compression of trace information
|
|
|
|
|
|
Simon Glass <sjg@chromium.org>
|
|
April 2013
|