Re: [dpdk-dev] [PATCH v2] build: disable compiler AVX512F support

["Wiles, Keith" <keith.wiles@intel.com>]

> On Nov 2, 2018, at 9:04 PM, Yongseok Koh <yskoh@mellanox.com> wrote:
> 
> This is a workaround to prevent a crash, which might be caused by
> optimization of newer gcc (7.3.0) on Intel Skylake.

Should the code below not also test for the gcc version and the Sky Lake processor, maybe I am wrong but it seems it is turning AVX512 for all GCC builds

Also bug 97 seems a bit obscure reference, maybe you know the bug report, but more details would be good?
> 
> Bugzilla ID: 97
> 
> Cc: stable@dpdk.org
> 
> Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
> ---
> 
> v2:
> * disable the flag only in case of gcc
> 
> config/x86/meson.build | 5 +++++
> mk/rte.cpuflags.mk     | 7 +++++++
> 2 files changed, 12 insertions(+)
> 
> diff --git a/config/x86/meson.build b/config/x86/meson.build
> index 33efb5e547..8ddca0ea9f 100644
> --- a/config/x86/meson.build
> +++ b/config/x86/meson.build
> @@ -47,6 +47,11 @@ endif
> if cc.get_define('__AVX512F__', args: march_opt) != ''
> 	dpdk_conf.set('RTE_MACHINE_CPUFLAG_AVX512F', 1)
> 	compile_time_cpuflags += ['RTE_CPUFLAG_AVX512F']
> +else
> +# disable AVX512F support of gcc as a workaround for Bug 97
> +	if cc.get_id() == 'gcc' and cc.has_argument('-mavx512f')
> +		machine_args += '-mno-avx512f'
> +	endif
> endif
> 
> dpdk_conf.set('RTE_CACHE_LINE_SIZE', 64)
> diff --git a/mk/rte.cpuflags.mk b/mk/rte.cpuflags.mk
> index 43ed84155b..a8c26fb011 100644
> --- a/mk/rte.cpuflags.mk
> +++ b/mk/rte.cpuflags.mk
> @@ -68,6 +68,13 @@ endif
> ifneq ($(filter $(AUTO_CPUFLAGS),__AVX512F__),)
> ifeq ($(CONFIG_RTE_ENABLE_AVX512),y)
> CPUFLAGS += AVX512F
> +else
> +# disable AVX512F support of gcc as a workaround for Bug 97
> +ifeq ($(CONFIG_RTE_TOOLCHAIN_GCC),y)
> +	ifeq ($(shell $(CC) --target-help | grep -q mavx512f && echo 1), 1)
> +		MACHINE_CFLAGS += -mno-avx512f
> +	endif
> +endif
> endif
> endif
> 
> -- 
> 2.11.0
> 

Regards,
Keith