Hi Fenghua,
On 12/3/24 8:16 PM, Fenghua Yu wrote:
> Hi, Babu,
>
> On 10/29/24 16:21, Babu Moger wrote:
>> Assign/unassign counters on resctrl group creation/deletion. Two counters
>> are required per group, one for MBM total event and one for MBM local
>> event.
>>
>> There are a limited number of counters available for assignment. If these
>> counters are exhausted, the kernel will display the error message: "Out of
>> MBM assignable counters". However, it is not necessary to fail the
>> creation of a group due to assignment failures. Users have the flexibility
>> to modify the assignments at a later time.
>>
>> Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
>> ---
>> v9: Changed rdtgroup_assign_cntrs() and rdtgroup_unassign_cntrs() to return void.
>> Updated couple of rdtgroup_unassign_cntrs() calls properly.
>> Updated function comments.
>>
>> v8: Renamed rdtgroup_assign_grp to rdtgroup_assign_cntrs.
>> Renamed rdtgroup_unassign_grp to rdtgroup_unassign_cntrs.
>> Fixed the problem with unassigning the child MON groups of CTRL_MON group.
>>
>> v7: Reworded the commit message.
>> Removed the reference of ABMC with mbm_cntr_assign.
>> Renamed the function rdtgroup_assign_cntrs to rdtgroup_assign_grp.
>>
>> v6: Removed the redundant comments on all the calls of
>> rdtgroup_assign_cntrs. Updated the commit message.
>> Dropped printing error message on every call of rdtgroup_assign_cntrs.
>>
>> v5: Removed the code to enable/disable ABMC during the mount.
>> That will be another patch.
>> Added arch callers to get the arch specific data.
>> Renamed fuctions to match the other abmc function.
>> Added code comments for assignment failures.
>>
>> v4: Few name changes based on the upstream discussion.
>> Commit message update.
>>
>> v3: This is a new patch. Patch addresses the upstream comment to enable
>> ABMC feature by default if the feature is available.
>> ---
>> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 61 +++++++++++++++++++++++++-
>> 1 file changed, 60 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index b0cce3dfd062..a8d21b0b2054 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -2932,6 +2932,46 @@ static void schemata_list_destroy(void)
>> }
>> }
>> +/*
>> + * Called when a new group is created. If "mbm_cntr_assign" mode is enabled,
>> + * counters are automatically assigned. Each group can accommodate two counters:
>> + * one for the total event and one for the local event. Assignments may fail
>> + * due to the limited number of counters. However, it is not necessary to fail
>> + * the group creation and thus no failure is returned. Users have the option
>> + * to modify the counter assignments after the group has been created.
>> + */
>> +static void rdtgroup_assign_cntrs(struct rdtgroup *rdtgrp)
>> +{
>> + struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
>> +
>> + if (!resctrl_arch_mbm_cntr_assign_enabled(r))
>> + return;
>> +
>> + if (is_mbm_total_enabled())
>> + rdtgroup_assign_cntr_event(r, rdtgrp, NULL, QOS_L3_MBM_TOTAL_EVENT_ID);
>
> In this code path,
> resctrl_mkdir()->resctrl_mkdir_ctrl_mon()->rdtgroup_assign_cntrs()->rdtgroup_assign_cntr_event()
>
> CPUs are not protected by read lock while rdtgroup_assign_cntr_event() walks r->mon_domains and run assing counters code on CPUs in the domains. Without CPU protection, r->mon_domains may race with CPU hotplug.
