Re: [PATCH] x86/cpu: Add AVX512_FP16 cpu feature

[Christophe de Dinechin <dinechin@redhat.com>]

On 2020-12-16 at 23:40 CET, Cathy Zhang wrote...
> AVX512 Half-precision floating point (FP16) has better performance
> compared to FP32 if the presicion or magnitude requirements are met.

spelling: precision

> It's defined as CPUID.(EAX=7,ECX=0):EDX[bit 23].
>
> Refer to
> https://software.intel.com/content/www/us/en/develop/download/\
> intel-architecture-instruction-set-extensions-programming-reference.html
>
> Signed-off-by: Cathy Zhang <cathy.zhang@intel.com>
> ---
>  target/i386/cpu.c | 2 +-
>  target/i386/cpu.h | 2 ++
>  2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index ca997a68cd..c4d623b8b9 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -979,7 +979,7 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
>              "avx512-vp2intersect", NULL, "md-clear", NULL,
>              NULL, NULL, "serialize", NULL,
>              "tsx-ldtrk", NULL, NULL /* pconfig */, NULL,
> -            NULL, NULL, NULL, NULL,
> +            NULL, NULL, NULL, "avx512-fp16",
>              NULL, NULL, "spec-ctrl", "stibp",
>              NULL, "arch-capabilities", "core-capability", "ssbd",
>          },
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index c4a49c06a8..6fd675c654 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -784,6 +784,8 @@ typedef uint64_t FeatureWordArray[FEATURE_WORDS];
>  #define CPUID_7_0_EDX_SERIALIZE         (1U << 14)
>  /* TSX Suspend Load Address Tracking instruction */
>  #define CPUID_7_0_EDX_TSX_LDTRK         (1U << 16)
> +/* AVX512_FP16 instruction */
> +#define CPUID_7_0_EDX_AVX512_FP16       (1U << 23)
>  /* Speculation Control */
>  #define CPUID_7_0_EDX_SPEC_CTRL         (1U << 26)
>  /* Single Thread Indirect Branch Predictors */


--
Cheers,
Christophe de Dinechin (IRC c3d)