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. Linux resctrl subsystem provides the interface to count maximum of two memory bandwidth events per group, from a combination of available total and local events. Keeping the current interface, users can enable a maximum of 2 ABMC counters per group. User will also have the option to enable only one counter to the group. If the system runs out of assignable ABMC counters, kernel will display an error. Users need to disable an already enabled counter to make space for new assignments. 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> Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx> --- Note: Checkpatch checks/warnings are ignored to maintain coding style. 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 | 3 +++ arch/x86/kernel/cpu/scattered.c | 1 + 3 files changed, 5 insertions(+) diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h index dd4682857c12..4c514cb245ff 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -473,6 +473,7 @@ #define X86_FEATURE_CLEAR_BHB_HW (21*32+ 3) /* BHI_DIS_S HW control enabled */ #define X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT (21*32+ 4) /* Clear branch history at vmexit using SW loop */ #define X86_FEATURE_FAST_CPPC (21*32 + 5) /* AMD Fast CPPC */ +#define X86_FEATURE_ABMC (21*32 + 6) /* 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 8bd84114c2d9..7e4d63b381d6 100644 --- a/arch/x86/kernel/cpu/cpuid-deps.c +++ b/arch/x86/kernel/cpu/cpuid-deps.c @@ -70,6 +70,9 @@ 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_ABMC, X86_FEATURE_BMEC }, { 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 c84c30188fdf..87f63e6b2994 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_PERFMON_V2, CPUID_EAX, 0, 0x80000022, 0 }, { X86_FEATURE_AMD_LBR_V2, CPUID_EAX, 1, 0x80000022, 0 }, { X86_FEATURE_AMD_LBR_PMC_FREEZE, CPUID_EAX, 2, 0x80000022, 0 }, -- 2.34.1
