Re: [PATCH v2 0/2] meson: ensure we enable CMPXCHG128 on x86_64

[Michael Tokarev]

07.10.2024 11:43, Paolo Bonzini wrote:
> Alex discovered that CMPXCHG128 was not enabled when building for
> x86_64, resulting in slow execution for wide atomic instructions,
> creating a huge contention when combined with a high number of cpus
> (found while booting android aarch64 guest on x86_64 host).
>
> The problem is that even though we enable -mcx16 option for x86_64, this
> is not used when testing for CMPXCHG128. Thus, we silently turn it off.
>
> x86_64 is the only architecture adding machine flags for now, so the
> problem is limited to this host architecture.  However, the problem
> is generic, so define a new variable for all the -m options, so that
> they can be used for other such tests in the future.
>
> Based-on: <20241004223715.1275428-1-pierrick.bouvier@linaro.org>
> Supersedes: <20241004220123.978938-1-pierrick.bouvier@linaro.org>
>
> Paolo Bonzini (2):
>    meson: define qemu_isa_flags
>    meson: ensure -mcx16 is passed when detecting ATOMIC128
>
>   meson.build | 33 ++++++++++++++++++++-------------
>   1 file changed, 20 insertions(+), 13 deletions(-)

Series:
Reviewed-By: Michael Tokarev <mjt@tls.msk.ru>

Yeah, this is exactly what I thought about when replying to email
by Pierrick Bouvier.  Well, with less details ofc :)

Thanks,

/mjt