Message-ID: <f4d5ddac-9399-4581-b914-ddebe1824463@amd.com>
Date: Wed, 21 Aug 2024 11:01:01 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net,
 fenghua.yu@...el.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com
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 tj@...nel.org, peterz@...radead.org, yanjiewtw@...il.com,
 kim.phillips@....com, lukas.bulwahn@...il.com, seanjc@...gle.com,
 jmattson@...gle.com, leitao@...ian.org, jpoimboe@...nel.org,
 rick.p.edgecombe@...el.com, kirill.shutemov@...ux.intel.com,
 jithu.joseph@...el.com, kai.huang@...el.com, kan.liang@...ux.intel.com,
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 ilpo.jarvinen@...ux.intel.com, peternewman@...gle.com,
 maciej.wieczor-retman@...el.com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, eranian@...gle.com, james.morse@....com
Subject: Re: [PATCH v6 16/22] x86/resctrl: Add the interface to unassign a MBM
 counter

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@....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.

> 
>> +{
>> +    struct rdt_mon_domain *d;
>> +
>> +    list_for_each_entry(d, &r->mon_domains, hdr.list)
>> +        if (test_bit(cntr_id, d->mbm_cntr_map))
>> +            return 1;
>> +
>> +    return 0;
>> +}
>> +
>> +/* Free the counter id after the event is unassigned */
>> +void rdtgroup_free_cntr(struct rdt_resource *r, struct rdtgroup *rdtgrp,
>> +            int index)
>> +{
>> +    /* Update the counter bitmap */
>> +    if (!rdtgroup_mbm_cntr_test(r, rdtgrp->mon.cntr_id[index])) {
>> +        mbm_cntr_free(rdtgrp->mon.cntr_id[index]);
>> +        rdtgrp->mon.cntr_id[index] = MON_CNTR_UNSET;
>> +    }
>> +}
>> +
>> +/*
>> + * Unassign a hardware counter from the group and update all the domains
>> + * in the group.
>> + */
>> +int rdtgroup_unassign_cntr(struct rdtgroup *rdtgrp, enum
>> resctrl_event_id evtid)
>> +{
>> +    struct rdt_resource *r =
>> &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
>> +    struct rdt_mon_domain *d;
>> +    int index;
>> +
>> +    index = mon_event_config_index_get(evtid);
>> +    if (index == INVALID_CONFIG_INDEX)
>> +        return -EINVAL;
>> +
>> +    if (rdtgrp->mon.cntr_id[index] != MON_CNTR_UNSET) {
>> +        list_for_each_entry(d, &r->mon_domains, hdr.list) {
>> +            resctrl_arch_assign_cntr(d, evtid, rdtgrp->mon.rmid,
>> +                         rdtgrp->mon.cntr_id[index],
>> +                         rdtgrp->closid, false);
>> +            clear_bit(rdtgrp->mon.cntr_id[index],
>> +                  d->mbm_cntr_map);
>> +        }
>> +
>> +        /* Free the counter at group level */
>> +        rdtgroup_free_cntr(r, rdtgrp, index);
> 
> rdtgroup_free_cntr() is called right after the counter has been unassigned
> from all domains. Will rdtgroup_mbm_cntr_test() thus not always return 0?
> It seems unnecessary to have rdtgroup_mbm_cntr_test() and considering that,
> rdtgroup_free_cntr() can just be open coded here?


Yes. We can open code here.

> 
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>>   /* rdtgroup information files for one cache resource. */
>>   static struct rftype res_common_files[] = {
>>       {
> 
> Reinette
> 

-- 
Thanks
Babu Moger

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