linux-kernel - Re: [PATCH v15 29/34] x86,fs/resctrl: Auto assign counters on mkdir and clean up on group removal

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Message-ID: <6dd38997-253f-4e89-88ef-b566039ff291@amd.com>
Date: Tue, 22 Jul 2025 18:59:51 -0500
From: "Moger, Babu" <bmoger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
 Babu Moger <babu.moger@....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 29/34] x86,fs/resctrl: Auto assign counters on mkdir
 and clean up on group removal

Hi Reinette,

On 7/17/2025 10:56 PM, Reinette Chatre wrote:
> Hi Babu,
> 
> On 7/8/25 3:17 PM, Babu Moger wrote:
>> Resctrl provides a user-configurable option mbm_assign_on_mkdir that
>> determines if a counter will automatically be assigned to an RMID, event
>> pair when its associated monitor group is created via mkdir.
>>
>> Enable mbm_assign_on_mkdir by default and automatically assign the counters
>> when a resctrl group is created.
>>
>> Counters allocated to a resctrl group should be released when the group is
>> deleted. Add support to unassign and free counters during the group
>> teardown.
>>
>> By default, each group requires two counters: one for the MBM total event
>> and one for the MBM local event.
>>
>> If the counters are exhausted, the kernel will log the error message
>> "Unable to allocate counter in domain" in
>> /sys/fs/resctrl/info/last_cmd_status when a new group is created and the
>> counter assignment will fail. However, the creation of a group should not
>> fail due to assignment failures. Users have the flexibility to modify the
>> assignments at a later time.
> 
> I find that this changelog jumps around a bit. Below is an attempt at some
> re-organization. Please feel free to improve:
> 
> 	Resctrl provides a user-configurable option mbm_assign_on_mkdir that
> 	determines if a counter will automatically be assigned to an RMID, event
> 	pair when its associated monitor group is created via mkdir.
>                                                                                  
> 	Enable mbm_assign_on_mkdir by default to automatically assign
> 	counters to the two default events (MBM total and MBM local) of a new
> 	monitoring group created via mkdir. This maintains backward compatibility
> 	with original resctrl support for these two events.
>                                                                                  
> 	Unassign and free counters belonging to a monitoring group when the group is
> 	deleted.
>                                                                                  
> 	Monitor group creation does not fail if a counter cannot be assigned to
> 	one or both events. There may be limited counters and users have the
> 	flexibility to modify counter assignments at a later time.
> 	Log the error message "Unable to allocate counter in domain" in
> 	/sys/fs/resctrl/info/last_cmd_status when a new monitoring group is created
> 	but counter assignment failed.
> 

Looks good. Thanks

>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
> 
> ...
> 
>> ---
>>   arch/x86/kernel/cpu/resctrl/monitor.c |  1 +
>>   fs/resctrl/rdtgroup.c                 | 70 ++++++++++++++++++++++++++-
>>   2 files changed, 69 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index 026c2e2d19d3..e0706083fe0e 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -457,6 +457,7 @@ int __init rdt_get_mon_l3_config(struct rdt_resource *r)
>>   		r->mon.mbm_cntr_assignable = true;
>>   		cpuid_count(0x80000020, 5, &eax, &ebx, &ecx, &edx);
>>   		r->mon.num_mbm_cntrs = (ebx & GENMASK(15, 0)) + 1;
>> +		r->mon.mbm_assign_on_mkdir = true;
> 
> This is a resctrl fs default. Should it not be set in
> resctrl_mon_resource_init()?
> 

Yes. Moved it in resctrl_mon_resource_init().

> 
>>   	}
>>   
>>   	r->mon_capable = true;
>> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
>> index b7289ce2b3a6..645245f274e9 100644
>> --- a/fs/resctrl/rdtgroup.c
>> +++ b/fs/resctrl/rdtgroup.c
>> @@ -2884,6 +2884,54 @@ static void schemata_list_destroy(void)
>>   	}
>>   }
>>   
>> +/*
>> + * rdtgroup_assign_cntrs() - Assign counters to MBM events. Called when
>> + *			     a new group is created.
>> + * If "mbm_event" counter assignment mode is enabled, counters should be
>> + * automatically assigned if the "mbm_assign_on_mkdir" is set.
>> + * Each group can accommodate two counters: one for the total event and
> 
> "Each group can accommodate two counters" -> "Each group can accommodate two counters
> per domain"?
> 
Sure.

>> + * one for the local event. Assignments may fail due to the limited number
>> + * of counters. However, it is not necessary to fail the group creation
>> + * and thus no failure is returned. Users have the option to modify the
>> + * counter assignments after the group has been created.
>> + */
>> +static void rdtgroup_assign_cntrs(struct rdtgroup *rdtgrp)
>> +{
>> +	struct rdt_resource *r = resctrl_arch_get_resource(RDT_RESOURCE_L3);
>> +
>> +	if (!r->mon_capable || !resctrl_arch_mbm_cntr_assign_enabled(r) ||
>> +	    !r->mon.mbm_assign_on_mkdir)
>> +		return;
>> +
>> +	if (resctrl_is_mon_event_enabled(QOS_L3_MBM_TOTAL_EVENT_ID))
>> +		rdtgroup_assign_cntr_event(NULL, rdtgrp,
>> +					   &mon_event_all[QOS_L3_MBM_TOTAL_EVENT_ID]);
>> +
>> +	if (resctrl_is_mon_event_enabled(QOS_L3_MBM_LOCAL_EVENT_ID))
>> +		rdtgroup_assign_cntr_event(NULL, rdtgrp,
>> +					   &mon_event_all[QOS_L3_MBM_LOCAL_EVENT_ID]);
>> +}
>> +
> 
> Reinette
> 
> 

Thanks
Babu