[PATCH v1 5/7] docs: mark intention to deprecate TCG tracing functionality

[Stefan Hajnoczi]

On Mon, May 17, 2021 at 11:47:11AM +0100, Alex Bennée wrote:
> 
> Daniel P. Berrangé <berrange at redhat.com> writes:
> 
> > On Wed, May 05, 2021 at 11:41:46AM +0100, Alex Bennée wrote:
> >> 
> >> Alex Bennée <alex.bennee at linaro.org> writes:
> >> 
> >> > Daniel P. Berrangé <berrange at 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
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