linux-kernel - Re: [PATCH v8 20/25] x86/resctrl: Report "Unassigned" for MBM events in mbm_cntr

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Message-ID: <c074fd31-f037-7da9-85f9-9cfde3b30716@amd.com>
Date: Fri, 18 Oct 2024 09:31:39 -0500
From: "Moger, Babu" <bmoger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
 Babu Moger <babu.moger@....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 v8 20/25] x86/resctrl: Report "Unassigned" for MBM events
 in mbm_cntr_assign mode

Hi Reinette,

On 10/15/2024 10:31 PM, Reinette Chatre wrote:
> Hi Babu,
> 
> On 10/9/24 10:39 AM, Babu Moger wrote:
>> In mbm_cntr_assign mode, the hardware counter should be assigned to read
>> the MBM events.
>>
>> Report "Unassigned" in case the user attempts to read the events without
>> assigning the counter.
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
>> v8: Used MBM_EVENT_ARRAY_INDEX to get the index for the MBM event.
>>      Documentation update to make the text generic.
>>
>> v7: Moved the documentation under "mon_data".
>>      Updated the text little bit.
>>
>> v6: Added more explaination in the resctrl.rst
>>      Added checks to detect "Unassigned" before reading RMID.
>>
>> v5: New patch.
>> ---
>>   Documentation/arch/x86/resctrl.rst        | 10 ++++++++++
>>   arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 13 ++++++++++++-
>>   2 files changed, 22 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
>> index 1b5c05a35793..99ee9c87952b 100644
>> --- a/Documentation/arch/x86/resctrl.rst
>> +++ b/Documentation/arch/x86/resctrl.rst
>> @@ -419,6 +419,16 @@ When monitoring is enabled all MON groups will also contain:
>>   	for the L3 cache they occupy). These are named "mon_sub_L3_YY"
>>   	where "YY" is the node number.
>>   
>> +	When supported the 'mbm_cntr_assign' mode allows users to assign a
>> +	counter to mon_hw_id, event pair enabling bandwidth monitoring for
>> +	as long as the counter remains assigned. The hardware will continue
>> +	tracking the assigned mon_hw_id until the user manually unassigns
>> +	it, ensuring that counters are not reset during this period. With
>> +	a limited number of counters, the system may run out of assignable
>> +	counters at some point. In that case, MBM event counters will return
> 
> nit: "at some point" can be dropped for clarity.

Sure.

> 
>> +	"Unassigned" when the event is read. Users must manually assign a
>> +	counter to read the events.
>> +
>>   "mon_hw_id":
>>   	Available only with debug option. The identifier used by hardware
>>   	for the monitor group. On x86 this is the RMID.
>> diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
>> index 50fa1fe9a073..5a9d15b2c319 100644
>> --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
>> +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
>> @@ -562,7 +562,7 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
>>   	struct rdtgroup *rdtgrp;
>>   	struct rdt_resource *r;
>>   	union mon_data_bits md;
>> -	int ret = 0;
>> +	int ret = 0, index;
>>   
>>   	rdtgrp = rdtgroup_kn_lock_live(of->kn);
>>   	if (!rdtgrp) {
>> @@ -576,6 +576,15 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
>>   	evtid = md.u.evtid;
>>   	r = &rdt_resources_all[resid].r_resctrl;
>>   
>> +	if (resctrl_arch_mbm_cntr_assign_enabled(r) && evtid != QOS_L3_OCCUP_EVENT_ID) {
>> +		index = MBM_EVENT_ARRAY_INDEX(evtid);
>> +		if (index != INVALID_CONFIG_INDEX &&
>> +		    rdtgrp->mon.cntr_id[index] == MON_CNTR_UNSET) {
>> +			rr.err = -ENOENT;
>> +			goto checkresult;
>> +		}
>> +	}
>> +
>>   	if (md.u.sum) {
>>   		/*
>>   		 * This file requires summing across all domains that share
>> @@ -613,6 +622,8 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
>>   		seq_puts(m, "Error\n");
>>   	else if (rr.err == -EINVAL)
>>   		seq_puts(m, "Unavailable\n");
>> +	else if (rr.err == -ENOENT)
>> +		seq_puts(m, "Unassigned\n");
>>   	else
>>   		seq_printf(m, "%llu\n", rr.val);
>>   
> 
> Reinette
> 

Thanks
- Babu Moger