linux-kernel - Re: [RFC PATCH v3 08/17] x86/resctrl: Initialize assignable counters bitmap

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Date: Tue, 7 May 2024 15:03:26 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.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: [RFC PATCH v3 08/17] x86/resctrl: Initialize assignable counters
 bitmap

Hi Reinette,

On 5/3/24 18:31, Reinette Chatre wrote:
> Hi Babu,
> 
> On 3/28/2024 6:06 PM, Babu Moger wrote:
>> AMD Hardware provides a set of counters when the ABMC feature is supported.
>> These counters are used for assigning events to the resctrl group.
>>
>> Introduce the bitmap assign_cntrs_free_map to allocate and free the
>> counters.
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>>
>> ---
>> v3: Changed the bitmap name to assign_cntrs_free_map. Removed abmc
>>     from the name.
>>
>> v2: Changed the bitmap name to assignable_counter_free_map from
>>     abmc_counter_free_map.
>> ---
>>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 19 +++++++++++++++++++
>>  1 file changed, 19 insertions(+)
>>
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index f49073c86884..2c7583e7b541 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -186,6 +186,22 @@ bool closid_allocated(unsigned int closid)
>>  	return !test_bit(closid, &closid_free_map);
>>  }
>>  
>> +static u64 assign_cntrs_free_map;
>> +static u32 assign_cntrs_free_map_len;
> 
> Please provide summary in comments about what these globals are and how they
> are used.
> 

Sure.

>> +
>> +static void assign_cntrs_init(void)
>> +{
>> +	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
>> +
>> +	if (r->mbm_assign_cntrs > 64) {
>> +		r->mbm_assign_cntrs = 64;
>> +		WARN(1, "Cannot support more than 64 Assignable counters\n");
> 
> I am a bit confused here. The configuration registers are introduced in patch #10
> and if I counted right there are 5 bits for the counter id. It thus seems to me
> as though there needs to be some checking during enumeration time to ensure
> that all counters enumerated can be configured.

Ok. I will remove this check here and move it to enumeration time in
rdt_get_mon_l3_config.

> 
>> +	}
>> +
>> +	assign_cntrs_free_map = BIT_MASK(r->mbm_assign_cntrs) - 1;
> 
> Please use bitmap API. For example, bitmap_fill()

Ok. Sure.

> 
>> +	assign_cntrs_free_map_len = r->mbm_assign_cntrs;
>> +}
>> +
>>  /**
>>   * rdtgroup_mode_by_closid - Return mode of resource group with closid
>>   * @closid: closid if the resource group
>> @@ -2459,6 +2475,9 @@ static int resctrl_abmc_setup(enum resctrl_res_level l, bool enable)
>>  	struct rdt_resource *r = &rdt_resources_all[l].r_resctrl;
>>  	struct rdt_domain *d;
>>  
>> +	/* Reset the counters bitmap */
>> +	assign_cntrs_init();
>> +
> 
> (At this point it is unclear when resctrl_abmc_setup() is called to understand
> if reset of bitmap may be appropriate. Please do expand all changelogs to help
> readers along with how this implementation is intended to work.)

resctrl_abmc_setup() is called either while enabling or disabling the ABMC
feature. In both these cases the bitmap assign_cntrs_free_map needs to be
reset.

Will add comments here,


> 
>>  	/* Update QOS_CFG MSR on all the CPUs in cpu_mask */
>>  	list_for_each_entry(d, &r->domains, list) {
>>  		on_each_cpu_mask(&d->cpu_mask, resctrl_abmc_msrwrite, &enable, 1);
> 
> Reinette
> 

-- 
Thanks
Babu Moger