RE: [PATCH v8 03/13] x86/cpufeatures: Add Bandwidth Monitoring Event Configuration feature flag

["Yu, Fenghua" <fenghua.yu@intel.com>]

Hi, Babu,

> Newer AMD processors support the new feature Bandwidth Monitoring Event
> Configuration (BMEC).
> 
> The feature support is identified via CPUID Fn8000_0020_EBX_x0 (ECX=0).
> Bits    Field Name    Description
> 3       EVT_CFG       Bandwidth Monitoring Event Configuration (BMEC)
> 
> Currently, the bandwidth monitoring events mbm_total_bytes and
> mbm_local_bytes are set to count all the total and local reads/writes
> respectively. With the introduction of slow memory, the two counters are not
> enough to count all the different types of memory events. With the feature
> BMEC, the users have the option to configure mbm_total_bytes and
> mbm_local_bytes to count the specific type of events.
> 
> Each BMEC event has a configuration MSR, QOS_EVT_CFG (0xc000_0400h +
> EventID) which contains one field for each bandwidth type that can be used to
> configure the bandwidth event to track any combination of supported
> bandwidth types. The event will count requests from every bandwidth type bit
> that is set in the corresponding configuration register.
> 
> Following are the types of events supported:
> 
> ====    ========================================================
> Bits    Description
> ====    ========================================================
> 6       Dirty Victims from the QOS domain to all types of memory
> 5       Reads to slow memory in the non-local NUMA domain
> 4       Reads to slow memory in the local NUMA domain
> 3       Non-temporal writes to non-local NUMA domain
> 2       Non-temporal writes to local NUMA domain
> 1       Reads to memory in the non-local NUMA domain
> 0       Reads to memory in the local NUMA domain
> ====    ========================================================
> 
> By default, the mbm_total_bytes configuration is set to 0x7F to count all the
> event types and the mbm_local_bytes configuration is set to
> 0x15 to count all the local memory events.
> 
> Feature description is available in the specification, "AMD64 Technology
> Platform Quality of Service Extensions, Revision: 1.03 Publication
> 
> Link: https://www.amd.com/en/support/tech-docs/amd64-technology-
> platform-quality-service-extensions
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> ---
>  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 d68b4c9c181d..6732ca0117be 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -306,6 +306,7 @@
>  #define X86_FEATURE_RSB_VMEXIT_LITE	(11*32+17) /* "" Fill RSB on VM
> exit when EIBRS is enabled */
>  #define X86_FEATURE_CALL_DEPTH		(11*32+18) /* "" Call depth
> tracking for RSB stuffing */
>  #define X86_FEATURE_SMBA		(11*32+19) /* Slow Memory
> Bandwidth Allocation */
> +#define X86_FEATURE_BMEC		(11*32+20) /* AMD Bandwidth
> Monitoring Event Configuration (BMEC) */
> 
>  /* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */
>  #define X86_FEATURE_AVX_VNNI		(12*32+ 4) /* AVX VNNI
> instructions */
> diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-
> deps.c
> index c881bcafba7d..4555f9596ccf 100644
> --- a/arch/x86/kernel/cpu/cpuid-deps.c
> +++ b/arch/x86/kernel/cpu/cpuid-deps.c
> @@ -68,6 +68,7 @@ static const struct cpuid_dep cpuid_deps[] = {
>  	{ X86_FEATURE_CQM_OCCUP_LLC,
> 	X86_FEATURE_CQM_LLC   },
>  	{ X86_FEATURE_CQM_MBM_TOTAL,
> 	X86_FEATURE_CQM_LLC   },
>  	{ X86_FEATURE_CQM_MBM_LOCAL,
> 	X86_FEATURE_CQM_LLC   },
> +	{ X86_FEATURE_BMEC,			X86_FEATURE_CQM_LLC   },

Shouldn't X86_FEATURE_BMEC really depend on X86_FEATURE_CQM_MBM_LOCAL and _TOTAL?

CQM_MBM_LOCAL and/or _TOTAL can be disabled but CQM_LLC can still be enabled. In this
case, BMEC shouldn't be enabled, right? But with this patch, BMEC will be enabled but it won't
work well as CQM_MBM_TOTAL/_LOCAL are not enabled.

You may remove the above line and add these two lines:

+	{ X86_FEATURE_BMEC,			X86_FEATURE_CQM_MBM_TOTAL   },  
+	{ X86_FEATURE_BMEC,			X86_FEATURE_CQM_MBM_LOCAL   },  

Thanks.

-Fenghua