linux-kernel - Re: [PATCH 1/2] Enumerate AVX Vector Neural Network instructions

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Message-ID: <8fa46290-28d8-5f61-1ce4-8e83bf911106@redhat.com>
Date:   Tue, 5 Jan 2021 12:47:23 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Yang Zhong <yang.zhong@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, bp@...en8.de
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        tony.luck@...el.com, seanjc@...gle.com, vkuznets@...hat.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org,
        kyung.min.park@...el.com, x86@...nel.org
Subject: Re: [PATCH 1/2] Enumerate AVX Vector Neural Network instructions

On 05/01/21 01:49, Yang Zhong wrote:
> From: Kyung Min Park <kyung.min.park@...el.com>
> 
> Add AVX version of the Vector Neural Network (VNNI) Instructions.
> 
> A processor supports AVX VNNI instructions if CPUID.0x07.0x1:EAX[4] is
> present. The following instructions are available when this feature is
> present.
>    1. VPDPBUS: Multiply and Add Unsigned and Signed Bytes
>    2. VPDPBUSDS: Multiply and Add Unsigned and Signed Bytes with Saturation
>    3. VPDPWSSD: Multiply and Add Signed Word Integers
>    4. VPDPWSSDS: Multiply and Add Signed Integers with Saturation
> 
> The only in-kernel usage of this is kvm passthrough. The CPU feature
> flag is shown as "avx_vnni" in /proc/cpuinfo.
> 
> This instruction is currently documented in the latest "extensions"
> manual (ISE). It will appear in the "main" manual (SDM) in the future.
> 
> Signed-off-by: Kyung Min Park <kyung.min.park@...el.com>
> Signed-off-by: Yang Zhong <yang.zhong@...el.com>
> Reviewed-by: Tony Luck <tony.luck@...el.com>
> ---
>   arch/x86/include/asm/cpufeatures.h | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index f5ef2d5b9231..d10d9962bd9b 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -293,6 +293,7 @@
>   #define X86_FEATURE_PER_THREAD_MBA	(11*32+ 7) /* "" Per-thread Memory Bandwidth Allocation */
>   
>   /* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */
> +#define X86_FEATURE_AVX_VNNI		(12*32+ 4) /* AVX VNNI instructions */
>   #define X86_FEATURE_AVX512_BF16		(12*32+ 5) /* AVX512 BFLOAT16 instructions */
>   
>   /* AMD-defined CPU features, CPUID level 0x80000008 (EBX), word 13 */
> 

Boris, is it possible to have a topic branch for this patch?