diff mbox series

[v7,01/12] x86/cpufeatures: Add Slow Memory Bandwidth Allocation feature flag

Message ID 166604557098.5345.506719195181543985.stgit@bmoger-ubuntu
State New
Headers
Series x86/resctrl: Support for AMD QoS new features |

Commit Message

Moger, Babu Oct. 17, 2022, 10:26 p.m. UTC 
  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://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@amd.com>
---
 arch/x86/include/asm/cpufeatures.h |    1 +
 arch/x86/kernel/cpu/scattered.c    |    1 +
 2 files changed, 2 insertions(+)

Comments

Reinette Chatre Oct. 27, 2022, 6:49 p.m. UTC | #1 
Hi Babu,

On 10/17/2022 3:26 PM, Babu Moger wrote:
> ---
>  arch/x86/include/asm/cpufeatures.h |    1 +
>  arch/x86/kernel/cpu/scattered.c    |    1 +
>  2 files changed, 2 insertions(+)
> 

I see arch/x86/include/asm/cpufeatures.h patches that also include
a change to tools/arch/x86/include/asm/cpufeatures.h in support
of perf. I do not know the customs here but I see others
change both in the same patch and if it is not done together a separate
patch to tools/arch/x86/include/asm/cpufeatures.h would be required
anyway to address the inevitable perf build warning.

Reinette
Moger, Babu Oct. 27, 2022, 7:17 p.m. UTC | #2 
Hi Reinette,

On 10/27/22 13:49, Reinette Chatre wrote:
> Hi Babu,
>
> On 10/17/2022 3:26 PM, Babu Moger wrote:
>> ---
>>  arch/x86/include/asm/cpufeatures.h |    1 +
>>  arch/x86/kernel/cpu/scattered.c    |    1 +
>>  2 files changed, 2 insertions(+)
>>
> I see arch/x86/include/asm/cpufeatures.h patches that also include
> a change to tools/arch/x86/include/asm/cpufeatures.h in support
> of perf. I do not know the customs here but I see others
> change both in the same patch and if it is not done together a separate
> patch to tools/arch/x86/include/asm/cpufeatures.h would be required
> anyway to address the inevitable perf build warning.

Lately, I see that these two files are synced after the feature bits are
committed. I can send the separate once these changes are committed.

Thanks

Babu
diff mbox series

Patch

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index b71f4f2ecdd5..583b88bcc7e1 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 fc01f81f6e2a..5a5f17ed69a2 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 },
 	{ X86_FEATURE_AMD_LBR_V2,	CPUID_EAX,  1, 0x80000022, 0 },
 	{ 0, 0, 0, 0, 0 }