Re: [Minios-devel] [UNIKRAFT PATCH 8/8] doc/guides: Add section about tracepoints

[Costin Lupu <costin.lup@xxxxxxxxx>]

Hi Yuri,

I didn't know where to say this so I'm going to leave it here,
considering it's a documentation issue.

We have tracepoint definitions and tracepoint values, this is a very
important information which I didn't find anywhere. The sections
contains them both. How? Well that's not obvious either. Please add some
explanations about the main idea about tracepoints: how they are stored
and/or serialized, how that information is later read and so on.

AFAIK this is was inspired by OSv, right? There is no mention about that
and I think it would be nice to do that (1) for paying credit and (2)
for having the original implementation as a reference if things get messy.

Thanks,
Costin

On 5/10/19 9:29 PM, Yuri Volchkov wrote:
> Signed-off-by: Yuri Volchkov <yuri.volchkov@xxxxxxxxx>
> ---
>  doc/guides/developers-debugging.rst | 48 +++++++++++++++++++++++++++++
>  1 file changed, 48 insertions(+)
> 
> diff --git a/doc/guides/developers-debugging.rst 
> b/doc/guides/developers-debugging.rst
> index 0e8799c4..cc7bc0ea 100644
> --- a/doc/guides/developers-debugging.rst
> +++ b/doc/guides/developers-debugging.rst
> @@ -72,3 +72,51 @@ You can then connect gdb within a separate console and 
> you're ready to debug: ::
>  You should be also able to use the debugging file
>  (``build/helloworld_linuxu-x86_64.dbg``) for gdb instead passing the kernel
>  image.
> +
> +============================
> +Trace points
> +============================
> +
> +Tracepoints are provided by libukdebug. To make Unikraft collect
> +tracing data enable the option `CONFIG_LIBUKDEBUG_TRACEPOINTS` in your
> +config (via ``make menuconfig``).
> +
> +Because tracepoints can noticeably affect performance, selective
> +enabling is implemented. Option `CONFIG_LIBUKDEBUG_TRACEPOINTS` just
> +enables the functionality, but all the tracepoints are compiled into
> +nothing by default (have no effect). If you would like one library to
> +collect tracing data, add to it's Makefile.uk ::
> +
> +   LIBAPPNAME_CFLAGS += -DUK_DEBUG_TRACE
> +
> +If you need just the information about tracepoints in one file, just
> +define `UK_DEBUG_TRACE` **before** ``#include <uk/trace.h>``.
> +
> +If you wish to enable **ALL** existing tracepoints, enable
> +`CONFIG_LIBUKDEBUG_ALL_TRACEPOINTS` in menuconfig.
> +
> +To read the collected data you have 2 options:
> +
> +1. Inside gdb
> +
> +2. Using trace.py
> +
> +For the first option, attach gdb to your running instance, and load
> +Unikraft gdb extension: ::
> +
> +  source support/scripts/uk-gdb.py
> +
> +Now you can print tracing log by issuing command ``uk
> +trace``. Alternatively, you can save all trace data into a binary file
> +with ``uk trace save <filename>``. This tracefile can be processed
> +later offline with trace.py script: ::
> +
> +  support/scripts/trace.py list <filename>
> +
> +Which brings us to the second option. Trace.py can run gdb and fetch
> +the tracefile for you. Just run: ::
> +
> +  support/scripts/trace.py fetch  <your_unikraft_image>.dbg
> +
> +.. note:: The *.dbg image is required, as it have offline data needed
> +          for parsing the trace buffer.
> 

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