Re: [Qemu-devel] [PATCH] x86/cpu: Enable CLDEMOTE(Demote Cache Line) cpu feature

[Eduardo Habkost <ehabkost@redhat.com>]

On Fri, May 04, 2018 at 11:57:33AM +0800, Jingqi Liu wrote:
> The CLDEMOTE instruction hints to hardware that the cache line that
> contains the linear address should be moved("demoted") from
> the cache(s) closest to the processor core to a level more distant
> from the processor core. This may accelerate subsequent accesses
> to the line by other cores in the same coherence domain,
> especially if the line was written by the core that demotes the line.
> 
> Intel Snow Ridge has added new cpu feature, CLDEMOTE.
> The new cpu feature needs to be exposed to guest VM.
> 
> The bit definition:
> CPUID.(EAX=7,ECX=0):ECX[bit 25] CLDEMOTE
> 
> The release document ref below link:
> https://software.intel.com/sites/default/files/managed/c5/15/\
> architecture-instruction-set-extensions-programming-reference.pdf
> 
> Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>

Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>

Queued, thanks.

> ---
>  target/i386/cpu.c | 2 +-
>  target/i386/cpu.h | 1 +
>  2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index ec1efd3..d5a5abf 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -483,7 +483,7 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
>              "avx512bitalg", NULL, "avx512-vpopcntdq", NULL,
>              "la57", NULL, NULL, NULL,
>              NULL, NULL, "rdpid", NULL,
> -            NULL, NULL, NULL, NULL,
> +            NULL, "cldemote", NULL, NULL,
>              NULL, NULL, NULL, NULL,
>          },
>          .cpuid_eax = 7,
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index 0c3f514..3ef90e0 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -678,6 +678,7 @@ typedef uint32_t FeatureWordArray[FEATURE_WORDS];
>  #define CPUID_7_0_ECX_AVX512_VPOPCNTDQ (1U << 14) /* POPCNT for vectors of DW/QW */
>  #define CPUID_7_0_ECX_LA57     (1U << 16)
>  #define CPUID_7_0_ECX_RDPID    (1U << 22)
> +#define CPUID_7_0_ECX_CLDEMOTE (1U << 25)  /* CLDEMOTE Instruction */
>  
>  #define CPUID_7_0_EDX_AVX512_4VNNIW (1U << 2) /* AVX512 Neural Network Instructions */
>  #define CPUID_7_0_EDX_AVX512_4FMAPS (1U << 3) /* AVX512 Multiply Accumulation Single Precision */
> -- 
> 1.8.3.1
> 
> 

-- 
Eduardo