RE: [PATCH V3 2/4] x86/resctrl: Enumerate per-thread MBA

[Babu Moger]

> -----Original Message-----
> From: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> Sent: Wednesday, May 6, 2020 6:50 PM
> To: tglx@xxxxxxxxxxxxx; fenghua.yu@xxxxxxxxx; bp@xxxxxxxxx;
> tony.luck@xxxxxxxxx
> Cc: kuo-lang.tseng@xxxxxxxxx; ravi.v.shankar@xxxxxxxxx; mingo@xxxxxxxxxx;
> Moger, Babu <Babu.Moger@xxxxxxx>; hpa@xxxxxxxxx; x86@xxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx; Reinette Chatre <reinette.chatre@xxxxxxxxx>
> Subject: [PATCH V3 2/4] x86/resctrl: Enumerate per-thread MBA
> 
> From: Fenghua Yu <fenghua.yu@xxxxxxxxx>
> 
> Some systems support per-thread Memory Bandwidth Allocation (MBA) which
> applies a throttling delay value to each hardware thread instead of to
> a core. Per-thread MBA is enumerated by CPUID.
> 
> No feature flag is shown in /proc/cpuinfo. User applications need to
> check a resctrl throttling mode info file to know if the feature is
> supported.
> 
> Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
> Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> ---
>  arch/x86/include/asm/cpufeatures.h | 1 +
>  arch/x86/kernel/cpu/cpuid-deps.c   | 1 +
>  arch/x86/kernel/cpu/scattered.c    | 1 +
>  3 files changed, 3 insertions(+)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h
> b/arch/x86/include/asm/cpufeatures.h
> index db189945e9b0..d0ec26ce7f66 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -286,6 +286,7 @@
>  #define X86_FEATURE_FENCE_SWAPGS_USER	(11*32+ 4) /* "" LFENCE in user
> entry SWAPGS path */
>  #define X86_FEATURE_FENCE_SWAPGS_KERNEL	(11*32+ 5) /* ""
> LFENCE in kernel entry SWAPGS path */
>  #define X86_FEATURE_SPLIT_LOCK_DETECT	(11*32+ 6) /* #AC for split lock
> */
> +#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_AVX512_BF16		(12*32+ 5) /* AVX512
> BFLOAT16 instructions */
> diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-
> deps.c
> index 3cbe24ca80ab..3e30b26c50ef 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_PER_THREAD_MBA,		X86_FEATURE_MBA
> },
>  	{}
>  };
> 
> diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
> index 62b137c3c97a..bccfc9ff3cc1 100644
> --- a/arch/x86/kernel/cpu/scattered.c
> +++ b/arch/x86/kernel/cpu/scattered.c
> @@ -35,6 +35,7 @@ static const struct cpuid_bit cpuid_bits[] = {
>  	{ X86_FEATURE_CDP_L3,		CPUID_ECX,  2, 0x00000010, 1
> },
>  	{ X86_FEATURE_CDP_L2,		CPUID_ECX,  2, 0x00000010, 2
> },
>  	{ X86_FEATURE_MBA,		CPUID_EBX,  3, 0x00000010, 0 },
> +	{ X86_FEATURE_PER_THREAD_MBA,	CPUID_ECX,  0, 0x00000010, 3
> },

This is a CPUID feature. You can actually detect this feature without
checking vendor model in patch @1. This patch looks good to me.

>  	{ X86_FEATURE_HW_PSTATE,	CPUID_EDX,  7, 0x80000007, 0 },
>  	{ X86_FEATURE_CPB,		CPUID_EDX,  9, 0x80000007, 0 },
>  	{ X86_FEATURE_PROC_FEEDBACK,    CPUID_EDX, 11, 0x80000007, 0 },
> --
> 2.21.0