[PATCH v1 5/7] docs: mark intention to deprecate TCG tracing functionality
alex.bennee at linaro.org
Wed May 5 10:35:16 UTC 2021
Daniel P. Berrangé <berrange at redhat.com> writes:
> On Wed, May 05, 2021 at 10:22:57AM +0100, Alex Bennée wrote:
>> Currently attempts to add a new TCG trace events results in failures
>> to build. Previous discussions have suggested maybe it's time to mark
>> the feature as deprecated and push people towards using plugins.
>> Signed-off-by: Alex Bennée <alex.bennee at linaro.org>
>> Cc: Luis Vilanova <vilanova at imperial.ac.uk>
>> Cc: Stefan Hajnoczi <stefanha at redhat.com>
>> docs/devel/tcg-plugins.rst | 2 ++
>> docs/devel/tracing.rst | 7 +++++++
>> docs/system/deprecated.rst | 13 +++++++++++++
>> 3 files changed, 22 insertions(+)
>> diff --git a/docs/devel/tcg-plugins.rst b/docs/devel/tcg-plugins.rst
>> index 18c6581d85..edf04e3091 100644
>> --- a/docs/devel/tcg-plugins.rst
>> +++ b/docs/devel/tcg-plugins.rst
>> @@ -3,6 +3,8 @@
>> Copyright (c) 2019, Linaro Limited
>> Written by Emilio Cota and Alex Bennée
>> +.. _tcgplugin-ref:
>> QEMU TCG Plugins
>> diff --git a/docs/devel/tracing.rst b/docs/devel/tracing.rst
>> index ba83954899..6b0f46cd54 100644
>> --- a/docs/devel/tracing.rst
>> +++ b/docs/devel/tracing.rst
>> @@ -414,6 +414,13 @@ disabled, this check will have no performance impact.
>> +.. warning::
>> + The ability to add new TCG trace points relies on a having a good
>> + understanding of the TCG internals. In the meantime TCG plugins
>> + have been introduced which solve many of the same problems with
>> + more of a focus on analysing guest code. See :ref:`tcgplugin-ref`
>> + for more details.
>> Guest code generated by TCG can be traced by defining an event with the "tcg"
>> event property. Internally, this property generates two events:
>> "<eventname>_trans" to trace the event at translation time, and
>> diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst
>> index 80cae86252..0c9d3c1e1e 100644
>> --- a/docs/system/deprecated.rst
>> +++ b/docs/system/deprecated.rst
>> @@ -312,6 +312,19 @@ The ``I7200`` guest CPU relies on the nanoMIPS ISA, which is deprecated
>> (the ISA has never been upstreamed to a compiler toolchain). Therefore
>> this CPU is also deprecated.
>> +TCG introspection features
>> +TCG trace-events (since 6.1)
>> +The ability to add new TCG trace points has bit rotted and as the
> When you say this "has bit rotted", just how bad is the situation ?
> Is the TCG tracing still usable at all, or is is fully broken
> already ?
Well patches 6/7 got it working for generic TCG things. I haven't been
able to get the architecture one working but I suspect that is some sort
of interaction between the per-arch trace header generation that I
haven't quite figured out yet.
It's currently broken without the included patches because it's not
really being exercised by anything.
>> +feature can be replicated with TCG plugins it will be deprecated. If
>> +any user is currently using this feature and needs help with
>> +converting to using TCG plugins they should contact the qemu-devel
>> +mailing list.
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