On Mon, Dec 07, 2020 at 07:34:40PM -0800, Kyung Min Park wrote:
> Enumerate AVX512 Half-precision floating point (FP16) CPUID feature
> flag. Compared with using FP32, using FP16 cut the number of bits
> required for storage in half, reducing the exponent from 8 bits to 5,
> and the mantissa from 23 bits to 10. Using FP16 also enables developers
> to train and run inference on deep learning models fast when all
> precision or magnitude (FP32) is not needed.
>
> A processor supports AVX512 FP16 if CPUID.(EAX=7,ECX=0):EDX[bit 23]
> is present. The AVX512 FP16 requires AVX512BW feature be implemented
> since the instructions for manipulating 32bit masks are associated with
> AVX512BW.
>
> The only in-kernel usage of this is kvm passthrough. The CPU feature
> flag is shown as "avx512_fp16" in /proc/cpuinfo.
>
> Signed-off-by: Kyung Min Park <kyung.min.park@xxxxxxxxx>
> Acked-by: Dave Hansen <dave.hansen@xxxxxxxxx>
> Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
> ---
> arch/x86/include/asm/cpufeatures.h | 1 +
> arch/x86/kernel/cpu/cpuid-deps.c | 1 +
> 2 files changed, 2 insertions(+)
>
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index b6b9b3407c22..bec37ec7101e 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -375,6 +375,7 @@
> #define X86_FEATURE_TSXLDTRK (18*32+16) /* TSX Suspend Load Address Tracking */
> #define X86_FEATURE_PCONFIG (18*32+18) /* Intel PCONFIG */
> #define X86_FEATURE_ARCH_LBR (18*32+19) /* Intel ARCH LBR */
> +#define X86_FEATURE_AVX512_FP16 (18*32+23) /* AVX512 FP16 */
> #define X86_FEATURE_SPEC_CTRL (18*32+26) /* "" Speculation Control (IBRS + IBPB) */
> #define X86_FEATURE_INTEL_STIBP (18*32+27) /* "" Single Thread Indirect Branch Predictors */
> #define X86_FEATURE_FLUSH_L1D (18*32+28) /* Flush L1D cache */
> diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
> index d502241995a3..42af31b64c2c 100644
> --- a/arch/x86/kernel/cpu/cpuid-deps.c
> +++ b/arch/x86/kernel/cpu/cpuid-deps.c
> @@ -69,6 +69,7 @@ static const struct cpuid_dep cpuid_deps[] = {
> { X86_FEATURE_CQM_MBM_TOTAL, X86_FEATURE_CQM_LLC },
> { X86_FEATURE_CQM_MBM_LOCAL, X86_FEATURE_CQM_LLC },
> { X86_FEATURE_AVX512_BF16, X86_FEATURE_AVX512VL },
> + { X86_FEATURE_AVX512_FP16, X86_FEATURE_AVX512BW },
> { X86_FEATURE_ENQCMD, X86_FEATURE_XSAVES },
> { X86_FEATURE_PER_THREAD_MBA, X86_FEATURE_MBA },
> {}
> --
Acked-by: Borislav Petkov <bp@xxxxxxx>
Paolo, you can pick those up if you prefer.
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
