linux-kernel - Re: [PATCH v13 04/27] x86/resctrl: Detect Assignable Bandwidth Monitoring feature details

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Message-ID: <a7ac2c4f-c8e2-4758-aa4e-3a706be4da6b@amd.com>
Date: Tue, 27 May 2025 15:15:43 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net,
 tony.luck@...el.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com
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 jpoimboe@...nel.org, alexandre.chartre@...cle.com,
 pawan.kumar.gupta@...ux.intel.com, thomas.lendacky@....com,
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Subject: Re: [PATCH v13 04/27] x86/resctrl: Detect Assignable Bandwidth
 Monitoring feature details

Hi Reinette,

On 5/22/25 15:54, Reinette Chatre wrote:
> Hi Babu,
> 
> On 5/15/25 3:51 PM, 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).
>>
>> Detect the feature and number of assignable monitoring counters supported.
>>
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
> 
> ...
> 
>> ---
>>  arch/x86/kernel/cpu/resctrl/monitor.c | 9 +++++++--
>>  include/linux/resctrl.h               | 4 ++++
>>  2 files changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index aeb2a9283069..fd2761d9f3f7 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -345,6 +345,7 @@ int __init rdt_get_mon_l3_config(struct rdt_resource *r)
>>  	unsigned int mbm_offset = boot_cpu_data.x86_cache_mbm_width_offset;
>>  	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
>>  	unsigned int threshold;
>> +	u32 eax, ebx, ecx, edx;
>>  
>>  	snc_nodes_per_l3_cache = snc_get_config();
>>  
>> @@ -375,13 +376,17 @@ int __init rdt_get_mon_l3_config(struct rdt_resource *r)
>>  	resctrl_rmid_realloc_threshold = resctrl_arch_round_mon_val(threshold);
>>  
>>  	if (rdt_cpu_has(X86_FEATURE_BMEC)) {
>> -		u32 eax, ebx, ecx, edx;
>> -
>>  		/* Detect list of bandwidth sources that can be tracked */
>>  		cpuid_count(0x80000020, 3, &eax, &ebx, &ecx, &edx);
>>  		r->mon.mbm_cfg_mask = ecx & MAX_EVT_CONFIG_BITS;
>>  	}
>>  
>> +	if (rdt_cpu_has(X86_FEATURE_ABMC)) {
>> +		r->mon.mbm_cntr_assignable = true;
>> +		cpuid_count(0x80000020, 5, &eax, &ebx, &ecx, &edx);
>> +		r->mon.num_mbm_cntrs = (ebx & GENMASK(15, 0)) + 1;
>> +	}
>> +
> 
> Shouldn't ABMC detection also include enumeration of which configurations
> are supported? From what I can tell, looking ahead patch #18 hardcodes definitions
> of all known "bandwidth types" (which term to use TBD) and then patch #20 allows
> *any* of these types to be configured irrespective of whether system
> supports it.
> AMD spec mentions "The types of L3 transactions that ABMC can track are
> configurable and identified by CPUID Fn8000_0020_ECX_x3."  It thus looks
> like the enumeration of r->mon.mbm_cfg_mask when BMEC is enabled is
> required for ABMC also and used by this implementation.
> 
>>  	r->mon_capable = true;
>>  
>>  	return 0;
>> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
>> index 2a8fa454d3e6..065fb6e38933 100644
>> --- a/include/linux/resctrl.h
>> +++ b/include/linux/resctrl.h
>> @@ -260,11 +260,15 @@ enum resctrl_schema_fmt {
>>   * @num_rmid:		Number of RMIDs available
>>   * @mbm_cfg_mask:	Bandwidth sources that can be tracked when bandwidth
>>   *			monitoring events can be configured.
>> + * @num_mbm_cntrs:	Number of assignable monitoring counters
>> + * @mbm_cntr_assignable:Is system capable of supporting monitor assignment?
> 
> "monitor assignment" has not been used so far, was this intended to be
> "counter assignment"?

Missed to respond to this comment.  Yes. Sure. Will correct it.
-- 
Thanks
Babu Moger