Usage Quick Reference
---------------------
-$ mount -t debugfs debugfs /debug
-$ echo mmiotrace > /debug/tracing/current_tracer
-$ cat /debug/tracing/trace_pipe > mydump.txt &
+$ mount -t debugfs debugfs /sys/kernel/debug
+$ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer
+$ cat /sys/kernel/debug/tracing/trace_pipe > mydump.txt &
Start X or whatever.
-$ echo "X is up" > /debug/tracing/trace_marker
-$ echo nop > /debug/tracing/current_tracer
+$ echo "X is up" > /sys/kernel/debug/tracing/trace_marker
+$ echo nop > /sys/kernel/debug/tracing/current_tracer
Check for lost events.
Usage
-----
-Make sure debugfs is mounted to /debug. If not, (requires root privileges)
-$ mount -t debugfs debugfs /debug
+Make sure debugfs is mounted to /sys/kernel/debug.
+If not (requires root privileges):
+$ mount -t debugfs debugfs /sys/kernel/debug
Check that the driver you are about to trace is not loaded.
Activate mmiotrace (requires root privileges):
-$ echo mmiotrace > /debug/tracing/current_tracer
+$ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer
Start storing the trace:
-$ cat /debug/tracing/trace_pipe > mydump.txt &
+$ cat /sys/kernel/debug/tracing/trace_pipe > mydump.txt &
The 'cat' process should stay running (sleeping) in the background.
Load the driver you want to trace and use it. Mmiotrace will only catch MMIO
accesses to areas that are ioremapped while mmiotrace is active.
During tracing you can place comments (markers) into the trace by
-$ echo "X is up" > /debug/tracing/trace_marker
+$ echo "X is up" > /sys/kernel/debug/tracing/trace_marker
This makes it easier to see which part of the (huge) trace corresponds to
which action. It is recommended to place descriptive markers about what you
do.
Shut down mmiotrace (requires root privileges):
-$ echo nop > /debug/tracing/current_tracer
+$ echo nop > /sys/kernel/debug/tracing/current_tracer
The 'cat' process exits. If it does not, kill it by issuing 'fg' command and
pressing ctrl+c.
events were lost, the trace is incomplete. You should enlarge the buffers and
try again. Buffers are enlarged by first seeing how large the current buffers
are:
-$ cat /debug/tracing/buffer_size_kb
+$ cat /sys/kernel/debug/tracing/buffer_size_kb
gives you a number. Approximately double this number and write it back, for
instance:
-$ echo 128000 > /debug/tracing/buffer_size_kb
+$ echo 128000 > /sys/kernel/debug/tracing/buffer_size_kb
Then start again from the top.
If you are doing a trace for a driver project, e.g. Nouveau, you should also
$ tar zcf pciid-nick-mmiotrace.tar.gz mydump.txt lspci.txt dmesg.txt
and then send the .tar.gz file. The trace compresses considerably. Replace
"pciid" and "nick" with the PCI ID or model name of your piece of hardware
-under investigation and your nick name.
+under investigation and your nickname.
How Mmiotrace Works
Access to hardware IO-memory is gained by mapping addresses from PCI bus by
calling one of the ioremap_*() functions. Mmiotrace is hooked into the
__ioremap() function and gets called whenever a mapping is created. Mapping is
-an event that is recorded into the trace log. Note, that ISA range mappings
+an event that is recorded into the trace log. Note that ISA range mappings
are not caught, since the mapping always exists and is returned directly.
MMIO accesses are recorded via page faults. Just before __ioremap() returns,
----------------
The raw log is text and easily filtered with e.g. grep and awk. One record is
-one line in the log. A record starts with a keyword, followed by keyword
-dependant arguments. Arguments are separated by a space, or continue until the
+one line in the log. A record starts with a keyword, followed by keyword-
+dependent arguments. Arguments are separated by a space, or continue until the
end of line. The format for version 20070824 is as follows:
-Explanation Keyword Space separated arguments
+Explanation Keyword Space-separated arguments
---------------------------------------------------------------------------
read event R width, timestamp, map id, physical, value, PC, PID
marker MARK timestamp, text
version VERSION the string "20070824"
info for reader LSPCI one line from lspci -v
-PCI address map PCIDEV space separated /proc/bus/pci/devices data
+PCI address map PCIDEV space-separated /proc/bus/pci/devices data
unk. opcode UNKNOWN timestamp, map id, physical, data, PC, PID
Timestamp is in seconds with decimals. Physical is a PCI bus address, virtual