Users can create as many monitor groups as RMIDs supported by the hardware. However, bandwidth monitoring feature on AMD system only guarantees that RMIDs currently assigned to a processor will be tracked by hardware. The counters of any other RMIDs which are no longer being tracked will be reset to zero. The MBM event counters return "Unavailable" for the RMIDs that are not tracked by hardware. So, there can be only limited number of groups that can give guaranteed monitoring numbers. With ever changing configurations there is no way to definitely know which of these groups are being tracked for certain point of time. Users do not have the option to monitor a group or set of groups for certain period of time without worrying about RMID being reset in between. The ABMC feature provides an option to the user to assign a hardware counter to an RMID, event pair and monitor the bandwidth as long as it is assigned. The assigned RMID will be tracked by the hardware until the user unassigns it manually. There is no need to worry about counters being reset during this period. Additionally, the user can specify a bitmask identifying the specific bandwidth types from the given source to track with the counter. Without ABMC enabled, monitoring will work in current mode without assignment option. The Linux resctrl subsystem provides an interface that allows monitoring of up to two memory bandwidth events per group, selected from a combination of available total and local events. When ABMC is enabled, two events will be assigned to each group by default, in line with the current interface design. Users will also have the option to configure which types of memory transactions are counted by these events. Due to the limited number of available counters (32), users may quickly exhaust the available counters. If the system runs out of assignable ABMC counters, the kernel will report an error. In such cases, users will nee dto unassign one or more active counters to free up countes for new assignments. The interface will provide options to assign or unassign events through the group-specific interface file. The feature can be detected via CPUID_Fn80000020_EBX_x00 bit 5. Bits Description 5 ABMC (Assignable Bandwidth Monitoring Counters) The feature details are documented in APM listed below [1]. [1] AMD64 Architecture Programmer's Manual Volume 2: System Programming Publication # 24593 Revision 3.41 section 19.3.3.3 Assignable Bandwidth Monitoring (ABMC). Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 Signed-off-by: Babu Moger <babu.moger@xxxxxxx> --- Note: Checkpatch checks/warnings are ignored to maintain coding style. v13: Updated the commit log with Linux interface details. v12: Removed the dependancy on X86_FEATURE_BMEC. Removed the Reviewed-by tag as patch has changed. v11: No changes. v10: No changes. v9: Took care of couple of minor merge conflicts. No other changes. v8: No changes. v7: Removed "" from feature flags. Not required anymore. https://lore.kernel.org/lkml/20240817145058.GCZsC40neU4wkPXeVR@fat_crate.local/ v6: Added Reinette's Reviewed-by. Moved the Checkpatch note below ---. v5: Minor rebase change and subject line update. v4: Changes because of rebase. Feature word 21 has few more additions now. Changed the text to "tracked by hardware" instead of active. v3: Change because of rebase. Actual patch did not change. v2: Added dependency on X86_FEATURE_BMEC. --- arch/x86/include/asm/cpufeatures.h | 1 + arch/x86/kernel/cpu/cpuid-deps.c | 2 ++ arch/x86/kernel/cpu/scattered.c | 1 + 3 files changed, 4 insertions(+) diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h index 6c2c152d8a67..d5c14dc678df 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -481,6 +481,7 @@ #define X86_FEATURE_AMD_HETEROGENEOUS_CORES (21*32 + 6) /* Heterogeneous Core Topology */ #define X86_FEATURE_AMD_WORKLOAD_CLASS (21*32 + 7) /* Workload Classification */ #define X86_FEATURE_PREFER_YMM (21*32 + 8) /* Avoid ZMM registers due to downclocking */ +#define X86_FEATURE_ABMC (21*32 + 9) /* Assignable Bandwidth Monitoring Counters */ /* * BUG word(s) diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c index a2fbea0be535..2f54831e04e5 100644 --- a/arch/x86/kernel/cpu/cpuid-deps.c +++ b/arch/x86/kernel/cpu/cpuid-deps.c @@ -71,6 +71,8 @@ static const struct cpuid_dep cpuid_deps[] = { { X86_FEATURE_CQM_MBM_LOCAL, X86_FEATURE_CQM_LLC }, { X86_FEATURE_BMEC, X86_FEATURE_CQM_MBM_TOTAL }, { X86_FEATURE_BMEC, X86_FEATURE_CQM_MBM_LOCAL }, + { X86_FEATURE_ABMC, X86_FEATURE_CQM_MBM_TOTAL }, + { X86_FEATURE_ABMC, X86_FEATURE_CQM_MBM_LOCAL }, { X86_FEATURE_AVX512_BF16, X86_FEATURE_AVX512VL }, { X86_FEATURE_AVX512_FP16, X86_FEATURE_AVX512BW }, { X86_FEATURE_ENQCMD, X86_FEATURE_XSAVES }, diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c index 16f3ca30626a..3b72b72270f1 100644 --- a/arch/x86/kernel/cpu/scattered.c +++ b/arch/x86/kernel/cpu/scattered.c @@ -49,6 +49,7 @@ static const struct cpuid_bit cpuid_bits[] = { { X86_FEATURE_MBA, CPUID_EBX, 6, 0x80000008, 0 }, { X86_FEATURE_SMBA, CPUID_EBX, 2, 0x80000020, 0 }, { X86_FEATURE_BMEC, CPUID_EBX, 3, 0x80000020, 0 }, + { X86_FEATURE_ABMC, CPUID_EBX, 5, 0x80000020, 0 }, { X86_FEATURE_AMD_WORKLOAD_CLASS, CPUID_EAX, 22, 0x80000021, 0 }, { X86_FEATURE_PERFMON_V2, CPUID_EAX, 0, 0x80000022, 0 }, { X86_FEATURE_AMD_LBR_V2, CPUID_EAX, 1, 0x80000022, 0 }, -- 2.34.1
