linux-kernel - Re: [PATCH v8 03/13] x86/cpufeatures: Add Bandwidth Monitoring Event Configuration feature flag

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Date:   Tue, 22 Nov 2022 16:09:18 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Babu Moger <babu.moger@....com>, <corbet@....net>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>
CC:     <fenghua.yu@...el.com>, <dave.hansen@...ux.intel.com>,
        <x86@...nel.org>, <hpa@...or.com>, <paulmck@...nel.org>,
        <akpm@...ux-foundation.org>, <quic_neeraju@...cinc.com>,
        <rdunlap@...radead.org>, <damien.lemoal@...nsource.wdc.com>,
        <songmuchun@...edance.com>, <peterz@...radead.org>,
        <jpoimboe@...nel.org>, <pbonzini@...hat.com>,
        <chang.seok.bae@...el.com>, <pawan.kumar.gupta@...ux.intel.com>,
        <jmattson@...gle.com>, <daniel.sneddon@...ux.intel.com>,
        <sandipan.das@....com>, <tony.luck@...el.com>,
        <james.morse@....com>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <bagasdotme@...il.com>,
        <eranian@...gle.com>
Subject: Re: [PATCH v8 03/13] x86/cpufeatures: Add Bandwidth Monitoring Event
 Configuration feature flag

Hi Babu,

On 11/4/2022 1:00 PM, Babu Moger wrote:
> 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

Looking at later patches it seems that it is not really 0xc000_0400h +
EventID but instead "0xc000_0400h + index_based_on_EventID"? This may be
too much detail for this changelog so maybe these specifics can
be deferred and just refer to the "configuration MSR".

> 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@....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) */

Surely a nitpick but it is strange that the two features introduced in this
series are described differently. Why does SMBA deserve the "AMD" prefix
but BMEC does not? I do not think the "(BMEC)" is necessary since
it is in X86_FEATURE_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   },
>  	{ X86_FEATURE_AVX512_BF16,		X86_FEATURE_AVX512VL  },
>  	{ X86_FEATURE_AVX512_FP16,		X86_FEATURE_AVX512BW  },
>  	{ X86_FEATURE_ENQCMD,			X86_FEATURE_XSAVES    },
> diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
> index 5a5f17ed69a2..67c4d24e06ef 100644
> --- a/arch/x86/kernel/cpu/scattered.c
> +++ b/arch/x86/kernel/cpu/scattered.c
> @@ -45,6 +45,7 @@ static const struct cpuid_bit cpuid_bits[] = {
>  	{ X86_FEATURE_PROC_FEEDBACK,    CPUID_EDX, 11, 0x80000007, 0 },
>  	{ X86_FEATURE_MBA,		CPUID_EBX,  6, 0x80000008, 0 },
>  	{ X86_FEATURE_SMBA,		CPUID_EBX,  2, 0x80000020, 0 },
> +	{ X86_FEATURE_BMEC,		CPUID_EBX,  3, 0x80000020, 0 },
>  	{ X86_FEATURE_PERFMON_V2,	CPUID_EAX,  0, 0x80000022, 0 },
>  	{ X86_FEATURE_AMD_LBR_V2,	CPUID_EAX,  1, 0x80000022, 0 },
>  	{ 0, 0, 0, 0, 0 }
> 
> 

Reinette