linux-kernel - Re: [PATCH v5 06/20] x86/resctrl: Add support to enable/disable AMD ABMC feature

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Message-ID: <f287fc4c-ece3-4914-bb17-fe1597517d65@arm.com>
Date: Fri, 16 Aug 2024 17:29:27 +0100
From: James Morse <james.morse@....com>
To: Babu Moger <babu.moger@....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,
 dave.hansen@...ux.intel.com, fenghua.yu@...el.com, mingo@...hat.com,
 tglx@...utronix.de, corbet@....net, bp@...en8.de,
 Reinette Chatre <reinette.chatre@...el.com>
Subject: Re: [PATCH v5 06/20] x86/resctrl: Add support to enable/disable AMD
 ABMC feature

Hello!

On 12/07/2024 23:05, Reinette Chatre wrote:
> On 7/3/24 2:48 PM, Babu Moger wrote:
>> Add the functionality to enable/disable AMD ABMC feature.
>>
>> AMD ABMC feature is enabled by setting enabled bit(0) in MSR
>> L3_QOS_EXT_CFG.  When the state of ABMC is changed, the MSR needs
>> to be updated on all the logical processors in the QOS Domain.
>>
>> Hardware counters will reset when ABMC state is changed. Reset the
>> architectural state so that reading of hardware counter is not considered
>> as an overflow in next update.
>>
>> The ABMC feature details are documented in APM listed below [1].
>> [1] AMD64 Architecture Programmer's Manual Volume 2: System Programming
>> Publication # 24593 Revision 3.41 section 19.3.3.3 Assignable Bandwidth
>> Monitoring (ABMC).

>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index 7e76f8d839fc..471fc0dbd7c3 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -2402,6 +2402,72 @@ int resctrl_arch_set_cdp_enabled(enum resctrl_res_level l, bool

>> +int resctrl_arch_abmc_enable(void)
>> +{
>> +    struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
>> +    struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
>> +    int ret = 0;
>> +
>> +    lockdep_assert_held(&rdtgroup_mutex);
>> +
>> +    if (r->mon.abmc_capable && !hw_res->abmc_enabled) {
>> +        ret = _resctrl_abmc_enable(r, true);
>> +        if (!ret)
>> +            hw_res->abmc_enabled = true;
>> +    }
>> +
>> +    return ret;

> resctrl_arch_abmc_enable() should probably keep returning an int even though
> this implementation does not need it since other archs may indeed return error.

Just as a datapoint on this: arm64 does indeed need to be able to return an error here.
This helper gets used to allocate all the monitors (and an array to hold them) which can fail.


Thanks,

James