Hi Babu, On 5/15/25 3:51 PM, Babu Moger wrote: > 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 "nee dto" -> "need to" "countes" -> "counters" > assignments. The interface will provide options to assign or unassign "The interface will" -> "resctrl will"? > events through the group-specific interface file. > > The feature can be detected via CPUID_Fn80000020_EBX_x00 bit 5. "The feature can be detected" -> "The feature is detected" > 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> > --- ... > 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 }, Is this dependency still accurate now that the implementation switched to the "extended event ID" variant of ABMC that no longer uses the event IDs associated with X86_FEATURE_CQM_MBM_TOTAL and 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 }, Reinette
