| Message ID | 20241007172317.1439564-1-pbonzini@redhat.com |
|---|---|
| Headers | show |
| Series | meson: ensure we enable CMPXCHG128 on x86_64 | expand |
07.10.2024 20:23, 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> > > v2->v3: collect *-by tags > append to qemu_isa_flags instead of prepending Yeah, this now looks much better wrt the appending, thank you for the v2! /mjt
On 10/7/24 10:23, Paolo Bonzini wrote: > v2->v3: collect *-by tags > append to qemu_isa_flags instead of prepending > > Paolo Bonzini (2): > meson: define qemu_isa_flags > meson: ensure -mcx16 is passed when detecting ATOMIC128 Reviewed-by: Richard Henderson <richard.henderson@linaro.org> r~
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> v2->v3: collect *-by tags append to qemu_isa_flags instead of prepending 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(-)