linux-kernel - Re: [PATCH v11 16/23] x86/resctrl: Add the functionality to unassigm MBM events

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Message-ID: <1ad70161-2046-4c7f-92c7-809b01c8c957@amd.com>
Date: Mon, 10 Feb 2025 10:23:03 -0600
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net,
 tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, tony.luck@...el.com, peternewman@...gle.com
Cc: x86@...nel.org, hpa@...or.com, paulmck@...nel.org,
 akpm@...ux-foundation.org, thuth@...hat.com, rostedt@...dmis.org,
 xiongwei.song@...driver.com, pawan.kumar.gupta@...ux.intel.com,
 daniel.sneddon@...ux.intel.com, jpoimboe@...nel.org, perry.yuan@....com,
 sandipan.das@....com, kai.huang@...el.com, xiaoyao.li@...el.com,
 seanjc@...gle.com, xin3.li@...el.com, andrew.cooper3@...rix.com,
 ebiggers@...gle.com, mario.limonciello@....com, james.morse@....com,
 tan.shaopeng@...itsu.com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, maciej.wieczor-retman@...el.com,
 eranian@...gle.com
Subject: Re: [PATCH v11 16/23] x86/resctrl: Add the functionality to unassigm
 MBM events

Hi Reinette,

On 2/5/25 21:54, Reinette Chatre wrote:
> Hi Babu,
> 
> subject: unassigm -> unassign

Sure.

> 
> On 1/22/25 12:20 PM, Babu Moger wrote:
>> The mbm_cntr_assign mode provides a limited number of hardware counters
> 
> (now back to "limited number of hardware counters")

How about?

The mbm_cntr_assign mode provides "num_mbm_cntrs" number of hardware counters

> 
>> that can be assigned to an RMID, event pair to monitor bandwidth while
>> assigned. If all counters are in use, the kernel will show an error
>> message: "Out of MBM assignable counters" when a new assignment is
>> requested. To make space for a new assignment, users must unassign an
> 
> To me "kernel will show an error" implies the kernel ring buffer. Please make
> the message accurate and mention that it will be in 
> last_cmd_status while also considering to use -ENOSPC to help user space.

If all the counters are in use, the kernel will log the error message
"Unable to allocate counter in domain" in /sys/fs/resctrl/info/
last_cmd_status when a new assignment is requested. To make space for a
new assignment, users must unassign an already assigned counter and retry
the assignment again.

> 
>> already assigned counter and retry the assignment again..
> 
> ".." -> "."
> 

Sure.

>>
>> Add the functionality to unassign and free the counters in the domain.
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
> 
> ...
> 
>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index 127c4000a81a..b6d188d0f9b7 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -1518,3 +1518,42 @@ int resctrl_assign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d,
>>  
>>  	return ret;
>>  }
>> +
>> +/*
>> + * Unassign and free the counter if assigned else return success.
>> + */
>> +static int resctrl_free_config_cntr(struct rdt_resource *r, struct rdt_mon_domain *d,
>> +				    struct rdtgroup *rdtgrp, enum resctrl_event_id evtid)
>> +{
>> +	int cntr_id, ret = 0;
>> +
>> +	cntr_id = mbm_cntr_get(r, d, rdtgrp, evtid);
>> +	if (cntr_id != -ENOENT) {
> 
> This can be simplified and indent level reduced with:
> 
> 	cntr_id = mbm_cntr_get(r, d, rdtgrp, evtid);
> 	if (cntr_id < 0)
> 		return ret;
> 

Sure.

>> +		ret = resctrl_config_cntr(r, d, evtid, rdtgrp->mon.rmid,
>> +					  rdtgrp->closid, cntr_id, false);
>> +		if (!ret)
>> +			mbm_cntr_free(d, cntr_id);
>> +	}
>> +
>> +	return ret;
>> +}
>> +
>> +/*
>> + * Unassign a hardware counter associated with @evtid from the domain and
>> + * the group. Unassign the counters from all the domains if @d is NULL else
>> + * unassign from @d.
>> + */
>> +int resctrl_unassign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d,
>> +				struct rdtgroup *rdtgrp, enum resctrl_event_id evtid)
>> +{
>> +	int ret = 0;
>> +
>> +	if (!d) {
>> +		list_for_each_entry(d, &r->mon_domains, hdr.list)
>> +			ret = resctrl_free_config_cntr(r, d, rdtgrp, evtid);
> 
> Same issue as previous patch wrt error handling.

Yes.

list_for_each_entry(d, &r->mon_domains, hdr.list) {
     ret = resctrl_free_config_cntr(r, d, rdtgrp, evtid);
     if (ret)
           return ret;
}

> 
>> +	} else {
>> +		ret = resctrl_free_config_cntr(r, d, rdtgrp, evtid);
>> +	}
>> +
>> +	return ret;
>> +}
> 
> Reinette
> 

-- 
Thanks
Babu Moger