Hi Babu, On 7/25/25 11:29 AM, 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 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> > --- Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx> Reinette
