Re: [PATCH v4 4/4] meson: Warn when TCI is selected but TCG backend is available

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Jan 26, 2021 at 05:24:10PM +0000, Alex Bennée wrote:
> 
> Stefan Weil <sw@weilnetz.de> writes:
> 
> > Am 25.01.21 um 23:35 schrieb Richard Henderson:
> >> On 1/25/21 11:02 AM, Stefan Weil wrote:
> >>> Am 25.01.21 um 20:02 schrieb Richard Henderson:
> >>>> On 1/25/21 8:58 AM, Stefan Weil wrote:
> >>>>> I have no evidence that TCI is less reliable than TCG, so I would not write
> >>>>> that.
> >>>> It can't pass make check-tcg.
> >>> Where does it fail? Maybe an expected timeout problem which can be solved by
> >>> increasing the timeouts for TCI?
> >>>
> >>> I have just run a local test of `make check-tcg` with native TCG and with TCI
> >>> and did not see a difference. But I noticed that in both cases many tests show
> >>> "skipped".
> >> You need to enable docker or podman for your development, so that you get all
> >> of the cross-compilers.
> >>
> >> Then:
> >>
> >>    TEST    fcvt on arm
> >> TODO ../qemu/tcg/tci.c:614: tcg_qemu_tb_exec()
> >> ../qemu/tcg/tci.c:614: tcg fatal error
> >> qemu: uncaught target signal 11 (Segmentation fault) - core dumped
> >>
> >>    TEST    float_convs on m68k
> >> TODO ../qemu/tcg/tci.c:614: tcg_qemu_tb_exec()
> >> ../qemu/tcg/tci.c:614: tcg fatal error
> >> qemu: uncaught target signal 11 (Segmentation fault) - core dumped
> >>
> >> which is of course one of the TODO assertions.
> >> It's positively criminal those still exist in the code.
> >
> >
> > I installed podman and repeated `make check-tcg`. The log file still 
> > shows 87 lines with "SKIPPED". There is also a gdb core dump, several 
> > warnings, but nothing related to TCI. Both tests cited above seem to 
> > work without a problem.
> 
> I'm going to go out on a limb and guess you have commit:
> 
>   23a77b2d18 (build-system: clean up TCG/TCI configury)
> 
> which temporarily has the effect of disabling TCI. See
> 
>   Subject: Re: [PATCH v4 1/4] configure: Fix --enable-tcg-interpreter
>   From: Paolo Bonzini <pbonzini@redhat.com>
>   Message-ID: <2b8b6291-b54c-b285-ae38-21f067a8497d@redhat.com>
>   Date: Mon, 25 Jan 2021 17:36:42 +0100
> 
> with that fix fixed I see the same failures as Richard:
> 
>   ./qemu-arm ./tests/tcg/arm-linux-user/fcvt > /dev/null
>   TODO ../../tcg/tci.c:614: tcg_qemu_tb_exec()
>   ../../tcg/tci.c:614: tcg fatal error
>   qemu: uncaught target signal 11 (Segmentation fault) - core dumped
>   fish: “./qemu-arm ./tests/tcg/arm-linu…” terminated by signal SIGSEGV (Address boundary error)
> 
> which does raise the question before today when was the last time anyone
> attempted to run check-tcg on this?
> 
> > The complete log file is available from 
> > https://qemu.weilnetz.de/test/check-tcg.txt.
> >
> > Daniel, regarding your comment: TCI has 100 % test coverage for the 
> > productive code lines.
> 
> By what tests? The fact you don't hit asserts in your day to day testing
> doesn't mean there are features missing that are easily tripped up or
> that TCI got it right.
> 
> > All code lines which were never tested raise an 
> > assertion, so can easily be identified (and fixed as soon as there is a 
> > test case which triggers such an assertion). The known deficits are 
> > speed, missing TCG opcodes, unimplemented TCG opcodes because of missing 
> > test cases and missing support for some host architectures.
> 
> Passing check-tcg would be a minimum for me.

Passing check-tcg *in gitlab CI* would be the minimum to consider
it on a par with TCG.

The lack of automated GitLab CI for TCI is a reason my proposed wording
described TCI as less reliable than native TCG. We can't claim it has
equivalent reliability unless we have equiv automated testing of TCI.

Regards,
Daniel
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