linux-kernel - Re: [PATCH v9 01/13] x86/cpufeatures: Add Slow Memory Bandwidth Allocation feature flag

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Date:   Thu, 15 Dec 2022 09:08:48 -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>, <christophe.leroy@...roup.eu>,
        <jarkko@...nel.org>, <adrian.hunter@...el.com>,
        <quic_jiles@...cinc.com>, <peternewman@...gle.com>
Subject: Re: [PATCH v9 01/13] x86/cpufeatures: Add Slow Memory Bandwidth
 Allocation feature flag

Hi Babu,

On 12/1/2022 7:36 AM, Babu Moger wrote:
> Add the new AMD feature X86_FEATURE_SMBA. With this feature, the QOS
> enforcement policies can be applied to external slow memory connected
> to the host. QOS enforcement is accomplished by assigning a Class Of
> Service (COS) to a processor and specifying allocations or limits for
> that COS for each resource to be allocated.
> 
> This feature is identified by the CPUID Function 8000_0020_EBX_x0.
> 
> CPUID Fn8000_0020_EBX_x0 AMD Bandwidth Enforcement Feature Identifiers
> (ECX=0)
> 
> Bits    Field Name      Description
> 2       L3SBE           L3 external slow memory bandwidth enforcement
> 
> CXL.memory is the only supported "slow" memory device. With the support
> of SMBA feature, the hardware enables bandwidth allocation on the slow
> memory devices. If there are multiple slow memory devices in the system,
> then the throttling logic groups all the slow sources together and
> applies the limit on them as a whole.
> 
> The presence of the SMBA feature(with CXL.memory) is independent of
> whether slow memory device is actually present in the system. If there
> is no slow memory in the system, then setting a SMBA limit will have no
> impact on the performance of the system.
> 
> Presence of CXL memory can be identified by numactl command.
> 
> $numactl -H
> available: 2 nodes (0-1)
> node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
> node 0 size: 63678 MB node 0 free: 59542 MB
> node 1 cpus:
> node 1 size: 16122 MB
> node 1 free: 15627 MB
> node distances:
> node   0   1
>    0:  10  50
>    1:  50  10
> 
> CPU list for CXL memory will be empty. The cpu-cxl node distance is
> greater than cpu-to-cpu distances. Node 1 has the CXL memory in this
> case. CXL memory can also be identified using ACPI SRAT table and
> memory maps.
> 
> Feature description is available in the specification, "AMD64
> Technology Platform Quality of Service Extensions, Revision: 1.03
> Publication # 56375 Revision: 1.03 Issue Date: February 2022".
> 
> 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>

According to "Ordering of commit tags" in Documentation/process/maintainer-tip.rst
the "Link:" tags should be after "Signed-off-by:". Could you please re-order
these to ensure this series is ready for the next stage?

> ---
>  arch/x86/include/asm/cpufeatures.h |    1 +
>  arch/x86/kernel/cpu/scattered.c    |    1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 11a0e06362e4..b6a45e56cd0c 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -307,6 +307,7 @@
>  #define X86_FEATURE_SGX_EDECCSSA	(11*32+18) /* "" SGX EDECCSSA user leaf function */
>  #define X86_FEATURE_CALL_DEPTH		(11*32+19) /* "" Call depth tracking for RSB stuffing */
>  #define X86_FEATURE_MSR_TSX_CTRL	(11*32+20) /* "" MSR IA32_TSX_CTRL (Intel) implemented */
> +#define X86_FEATURE_SMBA		(11*32+21) /* Slow 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 */
> diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
> index f53944fb8f7f..d925753084fb 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_CPB,		CPUID_EDX,  9, 0x80000007, 0 },
>  	{ 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_PERFMON_V2,	CPUID_EAX,  0, 0x80000022, 0 },
>  	{ X86_FEATURE_AMD_LBR_V2,	CPUID_EAX,  1, 0x80000022, 0 },
>  	{ 0, 0, 0, 0, 0 }
> 
> 

With the tag ordering addressed:

Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>

Thank you

Reinette