Re: [PATCH] mmiotrace: add user documentation

[Steven Rostedt]

On Sun, 13 Apr 2008, Pekka Paalanen wrote:
> +
> +Usage
> +-----
> +
> +Make sure debugfs is mounted to /debug. If not, (requires root privileges)
> +$ mount -t debugfs debugfs /debug
> +
> +Check that the driver you are about to trace is not loaded.
> +
> +Activate mmiotrace (requires root privileges):
> +$ echo mmiotrace > /debug/tracing/current_tracer
> +
> +Start storing the trace:
> +$ cat /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.
> +
> +[Unimplemented feature:]
> +During tracing you can place comments (markers) into the trace by
> +$ echo "X is up" > /debug/tracing/marker

I can implement a marker feature (logdev does this). I'll see if I can get
something working this week.

> +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 none > /debug/tracing/current_tracer

I need to still add a "save" of all previous tracing events. This is not
a trivial feature. It will require a little cleverness to make the new
trace doesn't start until all waiters have woken up and retrieved their
data. I'll see if I can get this implemented with some kind of completion.


> +The 'cat' process exits. If it does not, kill it by 'fg' and pressing ctrl+c.
> +
> +[This feature is not implemented yet!]
> +Check your kernel log. If there are messages about mmiotrace losing events,

This is something of higher priority to implement. I'll work on that
first.

> +this is due to buffer overrun, and the trace is incomplete. You should enlarge
> +the buffers and try again. [How?]

I pretty much have the infrastructure in place to implement this. Now it's
just time to do it ;-)

Thanks,

-- Steve

> +
> +If you are doing a trace for a driver project, e.g. Nouveau, you should also
> +do the following before sending your results:
> +$ lspci -vvv > lspci.txt
> +$ dmesg > dmesg.txt
> +$ 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.
> +
> +
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