Re: [PATCH v2 3/3] trace: recommend "log" backend for getting started with tracing

[Peter Maydell <peter.maydell@linaro.org>]

On Wed, 16 Dec 2020 at 16:09, Stefan Hajnoczi <stefanha@redhat.com> wrote:
>
> 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>
> ---
>  docs/devel/tracing.rst | 35 ++++++++++++++++++-----------------
>  1 file changed, 18 insertions(+), 17 deletions(-)
>
> diff --git a/docs/devel/tracing.rst b/docs/devel/tracing.rst
> index 76cc1b24fa..e60058bf55 100644
> --- a/docs/devel/tracing.rst
> +++ b/docs/devel/tracing.rst
> @@ -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::

Does --trace really not let you specify more than one pattern
without resorting to putting them into a file? That sounds like a
deficiency compared to -d (which allows -d trace:PATTERN,trace:PATTERN...)
that we could look at fixing...

Anyway,
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM