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@xxxxxxx>
Reviewed-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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
