[PATCH v1 5/7] docs: mark intention to deprecate TCG tracing functionality
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@linaro.org> Cc: Luis Vilanova <vilanova@imperial.ac.uk> Cc: Stefan Hajnoczi <stefanha@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. "tcg" ----- +.. 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 +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. + + Related binaries ---------------- -- 2.20.1
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@linaro.org> Cc: Luis Vilanova <vilanova@imperial.ac.uk> Cc: Stefan Hajnoczi <stefanha@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. "tcg" -----
+.. 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 ?
+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. +
Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
Daniel P. Berrangé <berrange@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@linaro.org> Cc: Luis Vilanova <vilanova@imperial.ac.uk> Cc: Stefan Hajnoczi <stefanha@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. "tcg" -----
+.. 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. +
Regards, Daniel
-- Alex Bennée
Alex Bennée <alex.bennee@linaro.org> writes:
Daniel P. Berrangé <berrange@redhat.com> writes:
On Wed, May 05, 2021 at 10:22:57AM +0100, Alex Bennée wrote: <snip>
+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.
Ahh it's since 7609ffb919 (trace: fix tcg tracing build breakage) which limited tcg/vcpu events to the root trace-events file. -- Alex Bennée
On Wed, May 05, 2021 at 11:41:46AM +0100, Alex Bennée wrote:
Alex Bennée <alex.bennee@linaro.org> writes:
Daniel P. Berrangé <berrange@redhat.com> writes:
On Wed, May 05, 2021 at 10:22:57AM +0100, Alex Bennée wrote: <snip>
+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.
Ahh it's since 7609ffb919 (trace: fix tcg tracing build breakage) which limited tcg/vcpu events to the root trace-events file.
That commit is from release 2.10.0. The other commit mentioned in patch 6 (73ff061032) is from 2.12.0. So no one has been able to use this feature for 3+ years already. Is it actually worth fixing and then deprecating for 2 releases before deleting, as opposed to just deleting the broken code today on basis that it can't have any current users ? Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
Daniel P. Berrangé <berrange@redhat.com> writes:
On Wed, May 05, 2021 at 11:41:46AM +0100, Alex Bennée wrote:
Alex Bennée <alex.bennee@linaro.org> writes:
Daniel P. Berrangé <berrange@redhat.com> writes:
On Wed, May 05, 2021 at 10:22:57AM +0100, Alex Bennée wrote: <snip>
+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.
Ahh it's since 7609ffb919 (trace: fix tcg tracing build breakage) which limited tcg/vcpu events to the root trace-events file.
That commit is from release 2.10.0.
The other commit mentioned in patch 6 (73ff061032) is from 2.12.0.
So no one has been able to use this feature for 3+ years already.
Is it actually worth fixing and then deprecating for 2 releases before deleting, as opposed to just deleting the broken code today on basis that it can't have any current users ?
Well I can get it up and running with the aforementioned patches and it seems reasonable to give some notice. I'm happy to defer to Stefan here though as it's his sub-system.
Regards, Daniel
-- Alex Bennée
On Mon, May 17, 2021 at 11:47:11AM +0100, Alex Bennée wrote:
Daniel P. Berrangé <berrange@redhat.com> writes:
On Wed, May 05, 2021 at 11:41:46AM +0100, Alex Bennée wrote:
Alex Bennée <alex.bennee@linaro.org> writes:
Daniel P. Berrangé <berrange@redhat.com> writes:
On Wed, May 05, 2021 at 10:22:57AM +0100, Alex Bennée wrote: <snip>
+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.
Ahh it's since 7609ffb919 (trace: fix tcg tracing build breakage) which limited tcg/vcpu events to the root trace-events file.
That commit is from release 2.10.0.
The other commit mentioned in patch 6 (73ff061032) is from 2.12.0.
So no one has been able to use this feature for 3+ years already.
Is it actually worth fixing and then deprecating for 2 releases before deleting, as opposed to just deleting the broken code today on basis that it can't have any current users ?
Well I can get it up and running with the aforementioned patches and it seems reasonable to give some notice. I'm happy to defer to Stefan here though as it's his sub-system.
Lluís Vilanova was the author and probably main user. He mentioned he's been away from QEMU for a while. If you want to drop the feature, I think that's fine since it has already been broken for over 3 years. If someone wants it back then it can be added via TCG plugins in the future. Stefan
participants (3)
-
Alex Bennée -
Daniel P. Berrangé -
Stefan Hajnoczi