Re: [PATCH v5 01/12] x86/cpufeatures: Add Slow Memory Bandwidth Allocation feature flag

["Moger, Babu" <babu.moger@amd.com>]

Hi Reinette,

On 9/29/22 16:58, Reinette Chatre wrote:
> Hi Babu,
>
> On 9/27/2022 1:25 PM, 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
>>
>>
>> Currently, 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&data=05%7C01%7Cbabu.moger%40amd.com%7Cdf869c35332b477dc5e808daa265c0cd%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638000855157338562%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=xFd6dFAZtT4jE9cPQ2LEkfxWAbG3ypQ0Mhl3K780YxI%3D&reserved=0
>> Link: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.kernel.org%2Fshow_bug.cgi%3Fid%3D206537&data=05%7C01%7Cbabu.moger%40amd.com%7Cdf869c35332b477dc5e808daa265c0cd%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638000855157338562%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=ZwBrgjVUvfriC0rM4z7XMP85CVhhI0erM%2BSFtdWa5%2B0%3D&reserved=0
>> Signed-off-by: Babu Moger <babu.moger@amd.com>
>> ---
>>  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 ef4775c6db01..349852b9daa4 100644
>> --- a/arch/x86/include/asm/cpufeatures.h
>> +++ b/arch/x86/include/asm/cpufeatures.h
>> @@ -304,6 +304,7 @@
>>  #define X86_FEATURE_UNRET		(11*32+15) /* "" AMD BTB untrain return */
>>  #define X86_FEATURE_USE_IBPB_FW		(11*32+16) /* "" Use IBPB during runtime firmware calls */
>>  #define X86_FEATURE_RSB_VMEXIT_LITE	(11*32+17) /* "" Fill RSB on VM exit when EIBRS is enabled */
>> +#define X86_FEATURE_SMBA		(11*32+18) /* 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 fd44b54c90d5..885ecf46abb2 100644
>> --- a/arch/x86/kernel/cpu/scattered.c
>> +++ b/arch/x86/kernel/cpu/scattered.c
>> @@ -44,6 +44,7 @@ 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 },
>>  	{ 0, 0, 0, 0, 0 }
>>  };
>>
>>
> Please respect the coding style of the area you are modifying.
> This is the same feedback as provided in v4 in
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2Fba36c68c-0b13-e8a2-fb45-8b84ea9f7259%40intel.com%2F&amp;data=05%7C01%7Cbabu.moger%40amd.com%7Cdf869c35332b477dc5e808daa265c0cd%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638000855157338562%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=WPFwZq1KCIhrGyGt5Qle9GYZBeXqTtHWGCTaK7vAeZY%3D&amp;reserved=0
>
> Looking ahead the same issue also remains in patch 3 as previously
> mentioned in v4 feedback.

Hmm.. I ran "./scripts/checkpatch.pl --strict --codespell" on all the
patches. The checkpatch didn't complain about this.

Now, looking at the line again, I see it should have been tabs between
those texts you are referring.

I will take care of it next revision.


> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2Fc4a9ea23-4280-d54c-263b-354ea321f746%40intel.com%2F&amp;data=05%7C01%7Cbabu.moger%40amd.com%7Cdf869c35332b477dc5e808daa265c0cd%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638000855157338562%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=4tuK0pMrJsiW44IKCkeZV8ujS4z9STOa3mKfRKbHulk%3D&amp;reserved=0
>
> Also missing is highlighting that configuration has changed from
> per-domain to per-CPU and why.

Already responded about this in patch 10.

Thanks

Babu

>
> It does not seem as though this series is ready. I will wait
> for next version to have existing review comments addressed before
> trying to look at new changes.
>
> Reinette

-- 
Thanks
Babu Moger