linux-kernel - Re: [PATCH v4 04/19] x86/resctrl: Detect Assignable Bandwidth Monitoring feature details

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Date: Tue, 18 Jun 2024 16:03:18 -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
Cc: x86@...nel.org, hpa@...or.com, paulmck@...nel.org, rdunlap@...radead.org,
 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,
 daniel.sneddon@...ux.intel.com, pbonzini@...hat.com, sandipan.das@....com,
 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 v4 04/19] x86/resctrl: Detect Assignable Bandwidth
 Monitoring feature details

Hi Reinette,

On 6/13/24 19:56, Reinette Chatre wrote:
> Hi Babu,
> 
> On 5/24/24 5:23 AM, Babu Moger wrote:
>> ABMC feature details are reported via CPUID Fn8000_0020_EBX_x5.
>> Bits Description
>> 15:0 MAX_ABMC Maximum Supported Assignable Bandwidth
>>       Monitoring Counter ID + 1
>>
>> 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).
>>
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
>> v4: Removed resctrl_arch_has_abmc(). Added all the code inline. We dont
>>      need to separate this as arch code.
>>
>> v3: Removed changes related to mon_features.
>>      Moved rdt_cpu_has to core.c and added new function
>> resctrl_arch_has_abmc.
>>      Also moved the fields mbm_assign_capable and mbm_assign_cntrs to
>>      rdt_resource. (James)
>>
>> v2: Changed the field name to mbm_assign_capable from abmc_capable.
>> ---
>>   arch/x86/kernel/cpu/resctrl/monitor.c | 14 ++++++++++++++
>>   include/linux/resctrl.h               |  4 ++++
>>   2 files changed, 18 insertions(+)
>>
>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c
>> b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index b35d04fc761b..1602b58ba23d 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -1066,6 +1066,20 @@ int __init rdt_get_mon_l3_config(struct
>> rdt_resource *r)
>>               mbm_local_event.configurable = true;
>>               mbm_config_rftype_init("mbm_local_bytes_config");
>>           }
>> +
>> +        if (rdt_cpu_has(X86_FEATURE_ABMC)) {
>> +            r->abmc_capable = true;
>> +            /*
>> +             * Query CPUID_Fn80000020_EBX_x05 for number of
>> +             * ABMC counters
>> +             */
>> +            cpuid_count(0x80000020, 5, &eax, &ebx, &ecx, &edx);
>> +            r->mon.num_cntrs = (ebx & 0xFFFF) + 1;
>> +            if (r->mon.num_cntrs > 64) {
>> +                WARN(1, "Cannot support more than 64 ABMC counters\n");
> 
> if (WARN_ON(...))

Sure..

> 
>> +                r->mon.num_cntrs = 64;
>> +            }
>> +        }
>>       }
>>         l3_mon_evt_init(r);
>> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
>> index bf99eb9c6ce4..24087e6efbb6 100644
>> --- a/include/linux/resctrl.h
>> +++ b/include/linux/resctrl.h
>> @@ -153,10 +153,12 @@ struct resctrl_schema;
>>   /**
>>    * struct resctrl_mon - Monitoring related data
>>    * @num_rmid:        Number of RMIDs available
>> + * @num_cntrs:        Maximum number of abmc counters
> 
> Maximum implies some limit and it is not clear what limit this applies to.
> Can this just be "Number of monitoring counters".

Sure.
> 
> Thinking ahead ... when switching between different "MBM modes" it
> may be that one mode has a different number of counters than the other.
> Since "ABMC" is just one mode it does not seem appropriate to
> connect the "num_cntrs" property to ABMC.

Ok

> 
> 
>>    * @evt_list:        List of monitoring events
>>    */
>>   struct resctrl_mon {
>>       int            num_rmid;
>> +    int            num_cntrs;
>>       struct list_head    evt_list;
>>   };
>>   @@ -177,6 +179,7 @@ struct resctrl_mon {
>>    * @parse_ctrlval:    Per resource function pointer to parse control
>> values
>>    * @fflags:        flags to choose base and info files
>>    * @cdp_capable:    Is the CDP feature available on this resource
>> + * @abmc_capable:    Is system capable of supporting monitor assignment?
>>    */
>>   struct rdt_resource {
>>       int            rid;
>> @@ -196,6 +199,7 @@ struct rdt_resource {
>>                            struct rdt_domain *d);
>>       unsigned long        fflags;
>>       bool            cdp_capable;
>> +    bool            abmc_capable;
> 
> Shouldn't abmc_capable be a property of the new struct resctrl_mon?

Sure. We can move it to resctrl_mon.

> 
>>   };
>>     /**
> 
> Reinette
> 

-- 
Thanks
Babu Moger