Re: [PATCH v6 16/22] x86/resctrl: Add the interface to unassign a MBM counter

["Moger, Babu" <bmoger@amd.com>]

Hi Reinette,

On 8/23/2024 3:18 PM, Reinette Chatre wrote:
> Hi Babu,
> 
> On 8/21/24 9:01 AM, Moger, Babu wrote:
>> Hi Reinette,
>>
>> On 8/16/24 16:41, Reinette Chatre wrote:
>>> Hi Babu,
>>>
>>> On 8/6/24 3:00 PM, Babu Moger wrote:
>>>> The ABMC feature provides an option to the user to assign a hardware
>>>
>>> This is about resctrl fs so "The ABMC feature" -> "mbm_cntr_assign mode"
>>
>> Sure.
>>
>>> (please check whole series).
>>
>> Sure.
>>
>>>
>>>> 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.
>>>>
>>>> Hardware provides only limited number of counters. If the system 
>>>> runs out
>>>> of assignable counters, kernel will display an error when a new 
>>>> assignment
>>>> is requested. Users need to unassign a already assigned counter to make
>>>> space for new assignment.
>>>>
>>>> Provide the interface to unassign the counter ids from the group. 
>>>> Free the
>>>> counter if it is not assigned in any of the domains.
>>>>
>>>> The feature details are documented in the 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@amd.com>
>>>> ---
>>>> v6: Removed mbm_cntr_free from this patch.
>>>>       Added counter test in all the domains and free if it is not
>>>> assigned to
>>>>       any domains.
>>>>
>>>> v5: Few name changes to match cntr_id.
>>>>       Changed the function names to
>>>>       rdtgroup_unassign_cntr
>>>>       More comments on commit log.
>>>>
>>>> v4: Added domain specific unassign feature.
>>>>       Few name changes.
>>>>
>>>> v3: Removed the static from the prototype of rdtgroup_unassign_abmc.
>>>>       The function is not called directly from user anymore. These
>>>>       changes are related to global assignment interface.
>>>>
>>>> v2: No changes.
>>>> ---
>>>>    arch/x86/kernel/cpu/resctrl/internal.h |  2 +
>>>>    arch/x86/kernel/cpu/resctrl/rdtgroup.c | 52 
>>>> ++++++++++++++++++++++++++
>>>>    2 files changed, 54 insertions(+)
>>>>
>>>> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h
>>>> b/arch/x86/kernel/cpu/resctrl/internal.h
>>>> index 4e8109dee174..cc832955b787 100644
>>>> --- a/arch/x86/kernel/cpu/resctrl/internal.h
>>>> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
>>>> @@ -689,6 +689,8 @@ int resctrl_arch_assign_cntr(struct rdt_mon_domain
>>>> *d, enum resctrl_event_id evt
>>>>                     u32 rmid, u32 cntr_id, u32 closid, bool assign);
>>>>    int rdtgroup_assign_cntr(struct rdtgroup *rdtgrp, enum
>>>> resctrl_event_id evtid);
>>>>    int rdtgroup_alloc_cntr(struct rdtgroup *rdtgrp, int index);
>>>> +int rdtgroup_unassign_cntr(struct rdtgroup *rdtgrp, enum
>>>> resctrl_event_id evtid);
>>>> +void rdtgroup_free_cntr(struct rdt_resource *r, struct rdtgroup
>>>> *rdtgrp, int index);
>>>>    void rdt_staged_configs_clear(void);
>>>>    bool closid_allocated(unsigned int closid);
>>>>    int resctrl_find_cleanest_closid(void);
>>>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>>>> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>>>> index 1ee91a7293a8..0c2215dbd497 100644
>>>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>>>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>>>> @@ -1961,6 +1961,58 @@ int rdtgroup_assign_cntr(struct rdtgroup 
>>>> *rdtgrp,
>>>> enum resctrl_event_id evtid)
>>>>        return 0;
>>>>    }
>>>>    +static int rdtgroup_mbm_cntr_test(struct rdt_resource *r, u32 
>>>> cntr_id)
>>>
>>> Could "test" be replaced with something more specific about what is 
>>> tested?
>>> for example, "rdtgroup_mbm_cntr_is_assigned()" or something better? The
>>
>> Yes. We can do that.
>>
>>> function
>>> looks like a good candidate for returning a bool.
>>
>> Sure.
>>>
>>> Is this function needed though? (more below)
>>
>> Yes. It is required. It is called from two places
>> (rdtgroup_unassign_update and rdtgroup_unassign_cntr).
>>
>> We can open code in rdtgroup_unassign_cntr. But we can't do that in
>> rdtgroup_unassign_update. But, I will check again for sure.
> 
> Similar to rdtgroup_assign_cntr() and rdtgroup_assign_update() discussed
> in previous patch, it also looks like rdtgroup_unassign_cntr() and
> rdtgroup_unassign_update() can be merged.

Yes. We can do that. Thanks

-- 
- Babu Moger