Messages in this thread | | | Date | Thu, 25 Aug 2022 17:42:45 -0500 | Subject | Re: [PATCH v3 02/10] x86/cpufeatures: Add Slow Memory Bandwidth Allocation feature flag | From | "Moger, Babu" <> |
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On 8/23/2022 5:47 PM, Reinette Chatre wrote: > Hi Babu, > > On 8/22/2022 6:42 AM, Babu Moger wrote: >> Adds 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 >> >> 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%7C4385e95126b24de58aec08da85597c88%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637968916632283680%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=dKSxIinxZGybtACbs3%2FVZr4zbeAvXYc%2FezVivq3xjx0%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%7C4385e95126b24de58aec08da85597c88%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637968916632283680%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=f7MJmrwkBGxq8BuWjNY6Ze9NdzJc6NOkXxNjUZk5c4U%3D&reserved=0 >> Signed-off-by: Babu Moger <babu.moger@amd.com> >> Reviewed-by: Ingo Molnar <mingo@kernel.org> >> --- > resctrl currently supports "memory bandwidth allocation" and this series adds > "slow memory bandwidth allocation". Could you please provide more detail about > what the difference is between "MBA" and "SMBA"? It is clear that the implementation In this case the slow memory means memory attached to CXL device. > treats them as different resources, but both resources are associated with L3 cache > domains and (from what I understand) throttling always occurs at the CPU. Can both > types of memory resources thus be seen as downstream from L3 cache? How can Yes. that is correct. They are seen as downstream from L3. > a user know what memory is considered when configuring MBA and what memory is > considered when configuring SMBA? Additionally, I do find the term "slow" to be
This memory completely transparent to OS with little bit higher latency that regular main memory.
Yes. I know slow word is bit vague. I am not an expert of CXL. But i see that word slow is being used to refer the CXL memory to differentiate it from regular memory.
> vague as a way to distinguish between different memory types. What is the > definition of "slow"? Would all "slow" memory on the system support SMBA?
Yes. All the slow memory in the system can support SMBA.
Thanks
Babu
> > Reinette
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