Hi Peter, On 2/27/24 12:26, Peter Newman wrote: > Hi Babu, > > On Tue, Feb 27, 2024 at 10:12 AM Moger, Babu <babu.moger@xxxxxxx> wrote: >> >> On 2/26/24 15:20, Reinette Chatre wrote: >>> >>> For example, if I understand correctly, theoretically, when ABMC is enabled then >>> "num_rmids" can be U32_MAX (after a quick look it is not clear to me why r->num_rmid >>> is not unsigned, tbd if number of directories may also be limited by kernfs). >>> User space could theoretically create more monitor groups than the number of >>> rmids that a resource claims to support using current upstream enumeration. >> >> CPU or task association still uses PQR_ASSOC(MSR C8Fh). There are only 11 >> bits(depends on specific h/w) to represent RMIDs. So, we cannot create >> more than this limit(r->num_rmid). >> >> In case of ABMC, h/w uses another counter(mbm_assignable_counters) with >> RMID to assign the monitoring. So, assignment limit is >> mbm_assignable_counters. The number of mon groups limit is still r->num_rmid. > > That is not entirely true. As long as you don't need to maintain > bandwidth counts for unassigned monitoring groups, there's no need to > allocate a HW RMID to a monitoring group. We don't need to allocate a h/w counter for unassigned group. My proposal is to allocate h/w counter only if user requests a assignment. The limit for assigned events at time is mbm_assignable_counters(32 right now). > > In my soft-ABMC prototype, where a limited number of HW RMIDs are > allocated to assigned monitoring groups, I was forced to replace the > HW RMID value stored in the task_struct to a pointer to the struct > mongroup, since the RMID value assigned to the mongroup would > frequently change, resulting in excessive walks down the tasklist to > find all of the tasks using the previous value. > > However, the number of hardware monitor group identifiers supported > (i.e., RMID, PARTID:PMG) is usually high enough that I don't think > there's much motivation to support unlimited monitoring groups. In > both soft-RMID and soft-ABMC, I didn't bother supporting more groups > than num_rmids, because the number was large enough. What is soft-ABMC? -- Thanks Babu Moger
