Hi Babu, On 7/3/24 2:48 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 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). Note: Checkpatch checks/warnings are ignored to maintain coding style.
This note may be more appropriate below the '---' separator line.
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
