Re: [PATCH v3] docs/devel: update tcg-plugins page

[Pierrick Bouvier <pierrick.bouvier@linaro.org>]

v2
--

rebased on top of master (plugins doc was split between several files)

v3
--

fix bad commit message

On 8/12/24 16:19, Pierrick Bouvier wrote:
> Reflect recent changes on API (inline ops) and new plugins.
> 
> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
> ---
>   docs/about/emulation.rst   | 49 ++++++++++++++++++++++++++++++++------
>   docs/devel/tcg-plugins.rst | 13 ++++++----
>   2 files changed, 50 insertions(+), 12 deletions(-)
> 
> diff --git a/docs/about/emulation.rst b/docs/about/emulation.rst
> index c03033e4e95..eea1261baac 100644
> --- a/docs/about/emulation.rst
> +++ b/docs/about/emulation.rst
> @@ -207,8 +207,8 @@ Once built a program can be run with multiple plugins loaded each with
>   their own arguments::
>   
>     $QEMU $OTHER_QEMU_ARGS \
> -      -plugin contrib/plugin/libhowvec.so,inline=on,count=hint \
> -      -plugin contrib/plugin/libhotblocks.so
> +      -plugin contrib/plugins/libhowvec.so,inline=on,count=hint \
> +      -plugin contrib/plugins/libhotblocks.so
>   
>   Arguments are plugin specific and can be used to modify their
>   behaviour. In this case the howvec plugin is being asked to use inline
> @@ -219,6 +219,14 @@ Linux user-mode emulation also evaluates the environment variable
>   
>     QEMU_PLUGIN="file=contrib/plugins/libhowvec.so,inline=on,count=hint" $QEMU
>   
> +QEMU plugins avoid to write directly to stdin/stderr, and use the log provided
> +by the API (see function ``qemu_plugin_outs``).
> +To show output, you may use this additional parameter::
> +
> +  $QEMU $OTHER_QEMU_ARGS \
> +    -d plugin \
> +    -plugin contrib/plugins/libhowvec.so,inline=on,count=hint
> +
>   Example Plugins
>   ~~~~~~~~~~~~~~~
>   
> @@ -260,8 +268,7 @@ Behaviour can be tweaked with the following arguments:
>     * - Option
>       - Description
>     * - inline=true|false
> -    - Use faster inline addition of a single counter. Not per-cpu and not
> -      thread safe.
> +    - Use faster inline addition of a single counter.
>     * - idle=true|false
>       - Dump the current execution stats whenever the guest vCPU idles
>   
> @@ -381,6 +388,15 @@ run::
>     160          1      0
>     135          1      0
>   
> +Test inline operations
> +......................
> +
> +``tests/plugins/inline.c``
> +
> +This plugin is used for testing all inline operations, conditional callbacks and
> +scoreboard. It prints a per-cpu summary of all events.
> +
> +
>   Hot Blocks
>   ..........
>   
> @@ -394,9 +410,6 @@ with linux-user execution as system emulation tends to generate
>   re-translations as blocks from different programs get swapped in and
>   out of system memory.
>   
> -If your program is single-threaded you can use the ``inline`` option for
> -slightly faster (but not thread safe) counters.
> -
>   Example::
>   
>     $ qemu-aarch64 \
> @@ -736,6 +749,28 @@ The plugin will log the reason of exit, for example::
>   
>     0xd4 reached, exiting
>   
> +Limit instructions per second
> +.............................
> +
> +This plugin can limit the number of Instructions Per Second that are executed::
> +
> +    # get number of instructions
> +    $ num_insn=$(./build/qemu-x86_64 -plugin ./build/tests/plugin/libinsn.so -d plugin /bin/true |& grep total | sed -e 's/.*: //')
> +    # limit speed to execute in 10 seconds
> +    $ time ./build/qemu-x86_64 -plugin ./build/contrib/plugins/libips.so,ips=$(($num_insn/10)) /bin/true
> +    real 10.000s
> +
> +
> +.. list-table:: IPS arguments
> +  :widths: 20 80
> +  :header-rows: 1
> +
> +  * - Option
> +    - Description
> +  * - ips=N
> +    - Maximum number of instructions per cpu that can be executed in one second.
> +      The plugin will sleep when the given number of instructions is reached.
> +
>   Other emulation features
>   ------------------------
>   
> diff --git a/docs/devel/tcg-plugins.rst b/docs/devel/tcg-plugins.rst
> index d8725c2854a..9463692c411 100644
> --- a/docs/devel/tcg-plugins.rst
> +++ b/docs/devel/tcg-plugins.rst
> @@ -61,11 +61,14 @@ translation event the plugin has an option to enumerate the
>   instructions in a block of instructions and optionally register
>   callbacks to some or all instructions when they are executed.
>   
> -There is also a facility to add an inline event where code to
> -increment a counter can be directly inlined with the translation.
> -Currently only a simple increment is supported. This is not atomic so
> -can miss counts. If you want absolute precision you should use a
> -callback which can then ensure atomicity itself.
> +There is also a facility to add inline instructions doing various operations,
> +like adding or storing an immediate value. It is also possible to execute a
> +callback conditionally, with condition being evaluated inline. All those inline
> +operations are associated to a ``scoreboard``, which is a thread-local storage
> +automatically expanded when new cores/threads are created and that can be
> +accessed/modified in a thread-safe way without any lock needed. Combining inline
> +operations and conditional callbacks offer a more efficient way to instrument
> +binaries, compared to classic callbacks.
>   
>   Finally when QEMU exits all the registered *atexit* callbacks are
>   invoked.