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>
>
> When doing a build for a target that already has the instruction sets for
> AVX2/AVX512 enabled, skip emitting the AVX compiler flags, or the
> skylake-avx512 '-march' flags, as they are unnecessary. Instead, when the
> default
> flags produce the desired output, just use them unmodified, and don't bother
> adding
> in extra enabling flags for AVX2 or AVX-512.
>
> Depends-on: series-35006 ("doc/linux_gsg: update recommended compiler
> versions")
>
> Signed-off-by: Bruce Richardson <bruce.richard...@intel.com>
> ---
>
> V4: Fix error flagged by CI with clang builds without AVX512 - change
> "cc_avx512_args" to correct "cc_avx512_flags"
>
> V3: put in version check to work around an issues with some meson
> versions, (hopefully) allowing builds to pass in all CIs. The
> printout of the extra flags now only happens with meson >= 0.60.2
>
> V2: dropped the doc update for the minimum compiler version. Based on
> discussion, that version bump is larger than proposed in RFC and is
> now a separate patch/series [series 35006 referenced above]
>
> ---
> config/x86/meson.build | 31 ++++++++++++++++++++-----------
> drivers/meson.build | 9 +--------
> lib/meson.build | 9 +--------
> 3 files changed, 22 insertions(+), 27 deletions(-)
>
> diff --git a/config/x86/meson.build b/config/x86/meson.build index
> c3564b0011..e6612dbd80 100644
> --- a/config/x86/meson.build
> +++ b/config/x86/meson.build
> @@ -4,11 +4,13 @@
> if is_ms_compiler
> cc_avx2_flags = ['/arch:AVX2']
> else
> - cc_avx2_flags = ['-mavx2']
> + cc_avx2_flags = []
> + if cc.get_define('__AVX2__', args: machine_args) == ''
> + cc_avx2_flags = ['-mavx2']
> + endif
> endif
>
> cc_has_avx512 = false
> -target_has_avx512 = false
>
> dpdk_conf.set('RTE_ARCH_X86', 1)
> if dpdk_conf.get('RTE_ARCH_64')
> @@ -65,26 +67,33 @@ if is_linux or cc.get_id() == 'gcc'
> endif
> endif
>
> -cc_avx512_flags = ['-mavx512f', '-mavx512vl', '-mavx512dq', '-mavx512bw', '-
> mavx512cd'] -if (binutils_ok and cc.has_multi_arguments(cc_avx512_flags)
> +avx512_march_flag = '-march=skylake-avx512'
> +cc_avx512_flags = []
> +if (binutils_ok and cc.has_argument(avx512_march_flag)
> and '-mno-avx512f' not in get_option('c_args'))
> # check if compiler is working with _mm512_extracti64x4_epi64
> # Ref: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82887
> code = '''#include <immintrin.h>
> void test(__m512i zmm){
> __m256i ymm = _mm512_extracti64x4_epi64(zmm, 0);}'''
> - result = cc.compiles(code, args : cc_avx512_flags, name : 'AVX512
> checking')
> + result = cc.compiles(code, args : [avx512_march_flag], name :
> + 'AVX512 checking')
> if result == false
> machine_args += '-mno-avx512f'
> warning('Broken _mm512_extracti64x4_epi64, disabling AVX512 support')
> else
> cc_has_avx512 = true
> - target_has_avx512 = (
> - cc.get_define('__AVX512F__', args: machine_args) != '' and
> - cc.get_define('__AVX512BW__', args: machine_args) != '' and
> - cc.get_define('__AVX512DQ__', args: machine_args) != '' and
> - cc.get_define('__AVX512VL__', args: machine_args) != ''
> - )
> + if cc.get_define('__AVX512F__', args: machine_args) == ''
> + cc_avx512_flags = [avx512_march_flag]
Hi Bruce, we have reviewed this internally and tested the same. We would like
your thought for the following.
- Before patch: we were directly setting AVX512 falgs for F, BW, DQ, VL
- new patch: we are setting the flags for `skylake-server` as bare minimal.
- AMD supports AVX512 from `znver4 and higher`.
As per GCC `https://gcc.gnu.org/onlinedocs/gcc/x86-Options.html`, the extra ISA
supported between skylake-server (super set) and znver4 and znver5 are `SAHF,
FXSR, XSAVE, RDRND, LZCNT, HLE, PREFETCHW, SGX`.
Currently for DPDK microbenchmarks and examples runs safe as it is not using
the `SAHF, FXSR, XSAVE, RDRND, LZCNT, HLE, PREFETCHW, SGX` instructions.
Question: should we check if target is `AMD EPYC` then apply bare minimum as
`-march=znver4`, thus avoid possible unsupported instruction generation when
non `c_args for march` is passed?
> + if cc.has_argument('-Wno-overriding-option')
> + cc_avx512_flags += '-Wno-overriding-option'
> + endif
> + endif
> + endif
> +endif
> +if developer_mode and meson.version().version_compare('>=0.60.2')
> + message('Extra C flags needed for AVX2 output:
> @0@'.format(cc_avx2_flags))
> + if cc_has_avx512
> + message('Extra C flags needed for AVX512 output:
> +@0@'.format(cc_avx512_flags))
> endif
> endif
>
> diff --git a/drivers/meson.build b/drivers/meson.build index
> b0850bbb24..51c824ea40 100644
> --- a/drivers/meson.build
> +++ b/drivers/meson.build
> @@ -267,18 +267,11 @@ foreach subpath:subdirs
> endif
> if sources_avx512.length() > 0 and cc_has_avx512
> cflags += '-DCC_AVX512_SUPPORT'
> - avx512_args = [cflags, cc_avx512_flags]
> - if not target_has_avx512 and cc.has_argument('-march=skylake-
> avx512')
> - avx512_args += '-march=skylake-avx512'
> - if cc.has_argument('-Wno-overriding-option')
> - avx512_args += '-Wno-overriding-option'
> - endif
> - endif
> avx512_lib = static_library(lib_name + '_avx512_lib',
> sources_avx512,
> dependencies: static_deps,
> include_directories: includes,
> - c_args: avx512_args)
> + c_args: [cflags, cc_avx512_flags])
> objs += avx512_lib.extract_objects(sources_avx512)
> endif
> endif
> diff --git a/lib/meson.build b/lib/meson.build index 41fd98f4e9..16389b9c34
> 100644
> --- a/lib/meson.build
> +++ b/lib/meson.build
> @@ -260,18 +260,11 @@ foreach l:libraries
> endif
> if sources_avx512.length() > 0 and cc_has_avx512
> cflags += '-DCC_AVX512_SUPPORT'
> - avx512_args = [cflags, cflags_avx512, cc_avx512_flags]
> - if not target_has_avx512 and
> cc.has_argument('-march=skylake-avx512')
> - avx512_args += '-march=skylake-avx512'
> - if cc.has_argument('-Wno-overriding-option')
> - avx512_args += '-Wno-overriding-option'
> - endif
> - endif
> avx512_lib = static_library(libname + '_avx512_lib',
> sources_avx512,
> dependencies: static_deps,
> include_directories: includes,
> - c_args: avx512_args)
> + c_args: [cflags, cflags_avx512, cc_avx512_flags])
> objs += avx512_lib.extract_objects(sources_avx512)
> endif
> endif
> --
> 2.48.1
