linux-kernel - Re: [PATCH v15 08/34] x86,fs/resctrl: Detect Assignable Bandwidth Monitoring feature details

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Message-ID: <f0b62df8-3582-4f94-bd06-cae2fe1451b1@amd.com>
Date: Mon, 21 Jul 2025 10:20:32 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net,
 tony.luck@...el.com, james.morse@....com, tglx@...utronix.de,
 mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com
Cc: Dave.Martin@....com, x86@...nel.org, hpa@...or.com,
 akpm@...ux-foundation.org, paulmck@...nel.org, rostedt@...dmis.org,
 Neeraj.Upadhyay@....com, david@...hat.com, arnd@...db.de, fvdl@...gle.com,
 seanjc@...gle.com, jpoimboe@...nel.org, pawan.kumar.gupta@...ux.intel.com,
 xin@...or.com, manali.shukla@....com, tao1.su@...ux.intel.com,
 sohil.mehta@...el.com, kai.huang@...el.com, xiaoyao.li@...el.com,
 peterz@...radead.org, xin3.li@...el.com, kan.liang@...ux.intel.com,
 mario.limonciello@....com, thomas.lendacky@....com, perry.yuan@....com,
 gautham.shenoy@....com, chang.seok.bae@...el.com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, peternewman@...gle.com, eranian@...gle.com
Subject: Re: [PATCH v15 08/34] x86,fs/resctrl: Detect Assignable Bandwidth
 Monitoring feature details

Hi Reinette,

On 7/17/25 13:45, Reinette Chatre wrote:
> Hi Babu,
> 
> On 7/8/25 3:17 PM, Babu Moger wrote:
>> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
>> index 267e9206a999..b48cc67cbbe3 100644
>> --- a/arch/x86/kernel/cpu/resctrl/core.c
>> +++ b/arch/x86/kernel/cpu/resctrl/core.c
>> @@ -990,7 +990,8 @@ void resctrl_cpu_detect(struct cpuinfo_x86 *c)
>>  
>>  	if (cpu_has(c, X86_FEATURE_CQM_OCCUP_LLC) ||
>>  	    cpu_has(c, X86_FEATURE_CQM_MBM_TOTAL) ||
>> -	    cpu_has(c, X86_FEATURE_CQM_MBM_LOCAL)) {
>> +	    cpu_has(c, X86_FEATURE_CQM_MBM_LOCAL) ||
>> +	    cpu_has(c, X86_FEATURE_ABMC)) {
> 
> I interpret this to mean that ABMC does not depend on any of the
> "legacy" monitoring features.
> 
>>  		u32 eax, ebx, ecx, edx;
>>  
>>  		/* QoS sub-leaf, EAX=0Fh, ECX=1 */
>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index 2558b1bdef8b..0a695ce68f46 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -339,6 +339,7 @@ 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();
>>  
>> @@ -368,14 +369,18 @@ int __init rdt_get_mon_l3_config(struct rdt_resource *r)
> 
> rdt_get_mon_l3_config() is only called when one or more of the "legacy" monitoring
> features are supported ...
> 
>>  	 */
>>  	resctrl_rmid_realloc_threshold = resctrl_arch_round_mon_val(threshold);
>>  
>> -	if (rdt_cpu_has(X86_FEATURE_BMEC)) {
>> -		u32 eax, ebx, ecx, edx;
>> -
>> +	if (rdt_cpu_has(X86_FEATURE_BMEC) || rdt_cpu_has(X86_FEATURE_ABMC)) {
>>  		/* 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)) {
> 
> ... so having this check within rdt_get_mon_l3_config() implies that ABMC depends
> on the "legacy" monitoring features. This contradicts the change to resctrl_cpu_detect()
> though so it seems that get_rdt_mon_resources() is missing a check for ABMC to ensure
> rdt_get_mon_l3_config() is called when ABMC is supported (but "legacy" monitoring features
> are not)?

Yes. That is correct. Added a new check in get_rdt_mon_resources().

diff --git a/arch/x86/kernel/cpu/resctrl/core.c
b/arch/x86/kernel/cpu/resctrl/core.c
index b48cc67cbbe3..09cb5a70b1cb 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -883,6 +883,8 @@ static __init bool get_rdt_mon_resources(void)
                resctrl_enable_mon_event(QOS_L3_MBM_LOCAL_EVENT_ID);
                ret = true;
        }
+       if (rdt_cpu_has(X86_FEATURE_ABMC))
+               ret = true;

        if (!ret)
                return false;

-- 
Thanks
Babu Moger