linux-kernel - Re: [RFC PATCH v3 07/17] x86/resctrl: Add support to enable/disable ABMC feature

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Date: Thu, 9 May 2024 16:45:43 -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 07/17] x86/resctrl: Add support to enable/disable
 ABMC feature

Hi Reinette,

On 5/7/24 15:32, Reinette Chatre wrote:
> Hi Babu,
> 
> On 5/7/2024 12:12 PM, Moger, Babu wrote:
>> On 5/3/24 18:30, Reinette Chatre wrote:
>>> On 3/28/2024 6:06 PM, Babu Moger wrote:
> 
> ...
> 
>>>>  /* MSR_IA32_VMX_MISC bits */
>>>>  #define MSR_IA32_VMX_MISC_INTEL_PT                 (1ULL << 14)
>>>> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
>>>> index 722388621403..8238ee437369 100644
>>>> --- a/arch/x86/kernel/cpu/resctrl/internal.h
>>>> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
>>>> @@ -96,6 +96,9 @@ cpumask_any_housekeeping(const struct cpumask *mask, int exclude_cpu)
>>>>  	return cpu;
>>>>  }
>>>>  
>>>> +/* ABMC ENABLE */
>>>
>>> Can this comment be made more useful?
>>
>> How about?
>> /* Setting bit 0 in L3_QOS_EXT_CFG enables ABMC features */
> 
> Regarding "ABMC features" - are there several features connected to
> "ABMC"?
> 

No. It should have been "ABMC feature". Will correct it.

>>
>> Or I can remove it totally.
>>
>>>
> 
> ...
> 
>>>> +int resctrl_arch_set_abmc_enabled(enum resctrl_res_level l, bool enable)
>>>> +{
>>>> +	struct rdt_hw_resource *hw_res = &rdt_resources_all[l];
>>>> +
>>>> +	if (!hw_res->r_resctrl.mbm_assign_capable)
>>>> +		return -EINVAL;
>>>> +
>>>> +	if (enable)
>>>> +		return resctrl_abmc_enable(l);
>>>> +
>>>> +	resctrl_abmc_disable(l);
>>>> +
>>>> +	return 0;
>>>> +}
>>>
>>> Why is resctrl_arch_set_abmc_enabled() necessary? It seem to add an unnecessary
>>> layer of abstraction.
>>>
>>
>> I feel it is better to keep it that way. It is consistent with definition
>> of resctrl_arch_set_cdp_enabled. It handles both enable and disable.
>> Otherwise we have add those checks from the caller.
> 
> Caller needs to know anyway whether to provide "true" or "false" to this function ...
> caller may as well just call the appropriate _enable()/_disable() variant, no?

Yes. We can call resctrl_abmc_enable() and resctrl_abmc_disable() directly.
Thanks
Babu Moger