Hi Babu, On Wed, Jul 9, 2025 at 12:18 AM Babu Moger <babu.moger@xxxxxxx> 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 during a particular time. Users do not have the option to > monitor a group or set of groups for a certain period of time without > worrying about RMID being reset in between. > > The ABMC feature allows users to assign a hardware counter to an RMID, > event pair and monitor bandwidth usage as long as it is assigned. The > hardware continues to track the assigned counter until it is explicitly > unassigned by the user. There is no need to worry about counters being > reset during this period. Additionally, the user can specify the type of > memory transactions (e.g., reads, writes) for the counter to track. > > 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 need > to unassign one or more active counters to free up counters for new > assignments. resctrl will provide options to assign or unassign events > through the group-specific interface file. > > The feature is 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. > > v15: Minor changelog update. > > v14: Removed the dependancy on X86_FEATURE_CQM_MBM_TOTAL and X86_FEATURE_CQM_MBM_LOCAL. > as discussed in https://lore.kernel.org/lkml/5f8b21c6-5166-46a6-be14-0c7c9bfb7cde@xxxxxxxxx/ > Need to re-work on ABMC enumeration during the init. > Updated changelog with few text update. > > 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/scattered.c | 1 + > 2 files changed, 2 insertions(+) > > diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h > index b78af55aa22e..d2950a0177cd 100644 > --- a/arch/x86/include/asm/cpufeatures.h > +++ b/arch/x86/include/asm/cpufeatures.h > @@ -490,6 +490,7 @@ > #define X86_FEATURE_PREFER_YMM (21*32+ 8) /* Avoid ZMM registers due to downclocking */ > #define X86_FEATURE_APX (21*32+ 9) /* Advanced Performance Extensions */ > #define X86_FEATURE_INDIRECT_THUNK_ITS (21*32+10) /* Use thunk for indirect branches in lower half of cacheline */ > +#define X86_FEATURE_ABMC (21*32+11) /* Assignable Bandwidth Monitoring Counters */ It looks like this bit has been taken by X86_FEATURE_TSA_SQ_NO. I had to move X86_FEATURE_ABMC down to (21*32+14) on tip/master. Thanks, -Peter > > /* > * BUG word(s) > diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c > index dbf6d71bdf18..d5d4a573aaf7 100644 > --- a/arch/x86/kernel/cpu/scattered.c > +++ b/arch/x86/kernel/cpu/scattered.c > @@ -50,6 +50,7 @@ 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 >
