On Tue, Feb 25, 2025 at 08:37:27AM -0800, Andre Muezerie wrote:
> On Tue, Feb 25, 2025 at 09:03:37AM +0000, Bruce Richardson wrote:
> > On Mon, Feb 24, 2025 at 01:01:18PM -0800, Andre Muezerie wrote:
> > > Top level 'cc_avx2_flags' was created and holds the correct flags
> > > depending on the compiler used.
> > >
> > > File meson.build was updated to handle the correct AVX512 flags
> > > depending on compiler used.
> > >
> > > Signed-off-by: Andre Muezerie <andre...@linux.microsoft.com>
> > > ---
> > > lib/acl/meson.build | 16 +++++++++-------
> > > 1 file changed, 9 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/lib/acl/meson.build b/lib/acl/meson.build
> > > index fefe131a48..24e47b6cc1 100644
> > > --- a/lib/acl/meson.build
> > > +++ b/lib/acl/meson.build
> > > @@ -19,7 +19,7 @@ if dpdk_conf.has('RTE_ARCH_X86')
> > > avx2_tmplib = static_library('avx2_tmp',
> > > 'acl_run_avx2.c',
> > > dependencies: static_rte_eal,
> > > - c_args: cflags + ['-mavx2'])
> > > + c_args: [cflags, cc_avx2_flags])
> > > objs += avx2_tmplib.extract_objects('acl_run_avx2.c')
> > >
> > > # compile AVX512 version if:
> > > @@ -38,6 +38,12 @@ if dpdk_conf.has('RTE_ARCH_X86')
> > > # compiler flags, and then have the .o file from static lib
> > > # linked into main lib.
> > >
> > > + if is_ms_compiler
> > > + acl_avx512_args = cc_avx512_flags
> > > + else
> > > + acl_avx512_args = ['-mavx512f', '-mavx512vl', '-mavx512cd',
> > > '-mavx512bw']
> > > + endif
> > > +
> >
> > in the non-msvc case are these flags not the same as cc_avx512_flags too?
> > If so, let's just get rid of the acl_avx512_args variable generally.
> >
> > /Bruce
>
> It's not an exact match. I did not look further to see if this was
> intentional or result
> of a typo. TBH I'm not even sure if it would be possible to deduct this from
> the code.
> Also, all the CPUs I have looked at bring all these 5 instruction sets
> together, but we
> know this might not hold true in the future as each one of them has an
> independent CPUID flag.
>
Yes, they are independent flags. However, given that AVX-512 has been
around a long time without any CPUs being released with only partial
support of the initial 5 sets introduced with the first AVX-512 CPUs, I'd
take the view that we are probably ok just mandating all 5 for AVX-512
support. That way, if it does happen that a CPU with partial support is
released, we just end up without AVX-512 support on it, rather than a
broken build. We can then fix that later if such a situation occurs. Until
such time, we get nice simplicity in our code of having a standard AVX-512
flag-set.
> cc_avx512_flags = ['-mavx512f', '-mavx512vl', '-mavx512dq', '-mavx512bw']
>
> My choice was to keep the flags that were used initially, but I can change
> that if the
> maintainers tell me this was a mistake.
I'd add in "avx512cd" into the basic avx512 flags and then reuse the
variable. I suspect I just missed it when creating the list of flags.
/Bruce
