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SubjectRE: [PATCH v9 01/13] x86/cpufeatures: Add Slow Memory Bandwidth Allocation feature flag
Date
[AMD Official Use Only - General]

Hi Reinette,

> -----Original Message-----
> From: Reinette Chatre <reinette.chatre@intel.com>
> Sent: Thursday, December 15, 2022 11:09 AM
> To: Moger, Babu <Babu.Moger@amd.com>; corbet@lwn.net;
> tglx@linutronix.de; mingo@redhat.com; bp@alien8.de
> Cc: fenghua.yu@intel.com; dave.hansen@linux.intel.com; x86@kernel.org;
> hpa@zytor.com; paulmck@kernel.org; akpm@linux-foundation.org;
> quic_neeraju@quicinc.com; rdunlap@infradead.org;
> damien.lemoal@opensource.wdc.com; songmuchun@bytedance.com;
> peterz@infradead.org; jpoimboe@kernel.org; pbonzini@redhat.com;
> chang.seok.bae@intel.com; pawan.kumar.gupta@linux.intel.com;
> jmattson@google.com; daniel.sneddon@linux.intel.com; Das1, Sandipan
> <Sandipan.Das@amd.com>; tony.luck@intel.com; james.morse@arm.com;
> linux-doc@vger.kernel.org; linux-kernel@vger.kernel.org;
> bagasdotme@gmail.com; eranian@google.com; christophe.leroy@csgroup.eu;
> jarkko@kernel.org; adrian.hunter@intel.com; quic_jiles@quicinc.com;
> peternewman@google.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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.
> > amd.com%2Fen%2Fsupport%2Ftech-docs%2Famd64-technology-platform-
> quality
> > -service-
> extensions&amp;data=05%7C01%7Cbabu.moger%40amd.com%7Cb03ef091
> >
> f14847baced108dadebfaa5a%7C3dd8961fe4884e608e11a82d994e183d%7C0%
> 7C0%7C
> >
> 638067212053430832%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMD
> AiLCJQIjo
> >
> iV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdat
> a=HF%2
> > BYN5rW5i8fw6588RXfgCKMSMF4EmZZ252Q0N7Mew0%3D&amp;reserved=0
> > Link:
> > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugz
> >
> illa.kernel.org%2Fshow_bug.cgi%3Fid%3D206537&amp;data=05%7C01%7Cbab
> u.m
> >
> oger%40amd.com%7Cb03ef091f14847baced108dadebfaa5a%7C3dd8961fe488
> 4e608e
> >
> 11a82d994e183d%7C0%7C0%7C638067212053430832%7CUnknown%7CTWFpb
> GZsb3d8ey
> >
> JWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7
> C300
> >
> 0%7C%7C%7C&amp;sdata=Im%2BiT7NDUpcgR0dAYFDJALge6Wf873MNLyntsyC
> MwlQ%3D&
> > amp;reserved=0
> > Signed-off-by: Babu Moger <babu.moger@amd.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?

Sure. Will change it.

>
> > ---
> > 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@intel.com>

Thanks
Babu
>
> Thank you
>
> Reinette

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