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Date: Thu, 27 Jun 2024 16:43:08 +0530
From: Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>
To: "Zhang, Rui" <rui.zhang@...el.com>,
"alexander.shishkin@...ux.intel.com" <alexander.shishkin@...ux.intel.com>,
"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
"Hunter, Adrian" <adrian.hunter@...el.com>,
"oleksandr@...alenko.name" <oleksandr@...alenko.name>,
"mingo@...hat.com" <mingo@...hat.com>,
"irogers@...gle.com" <irogers@...gle.com>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"gustavoars@...nel.org" <gustavoars@...nel.org>,
"kan.liang@...ux.intel.com" <kan.liang@...ux.intel.com>,
"kees@...nel.org" <kees@...nel.org>,
"mark.rutland@....com" <mark.rutland@....com>,
"peterz@...radead.org" <peterz@...radead.org>, "bp@...en8.de"
<bp@...en8.de>, "acme@...nel.org" <acme@...nel.org>,
"jolsa@...nel.org" <jolsa@...nel.org>, "x86@...nel.org" <x86@...nel.org>,
"namhyung@...nel.org" <namhyung@...nel.org>
Cc: "ravi.bangoria@....com" <ravi.bangoria@....com>,
"gautham.shenoy@....com" <gautham.shenoy@....com>,
"kprateek.nayak@....com" <kprateek.nayak@....com>,
"linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
"ananth.narayan@....com" <ananth.narayan@....com>,
"sandipan.das@....com" <sandipan.das@....com>,
"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v3 10/10] perf/x86/rapl: Add per-core energy counter
support for AMD CPUs
Hello Rui,
On 6/27/2024 12:19 PM, Zhang, Rui wrote:
> Hi, Dhananjay
>>
>>>
>>> [...]
>>>
>>>> @@ -685,6 +774,13 @@ static void __init rapl_advertise(void)
>>>> rapl_pkg_domain_names[i],
>>>> rapl_hw_unit[i]);
>>>> }
>>>> }
>>>> +
>>>> + for (i = 0; i < NR_RAPL_CORE_DOMAINS; i++) {
>>>> + if (rapl_core_cntr_mask & (1 << i)) {
>>>> + pr_info("hw unit of domain %s 2^-%d
>>>> Joules\n",
>>>> + rapl_core_domain_names[i],
>>>> rapl_hw_unit[i]);
>>>
>>> rapl_hw_unit[] is for package pmu only and
>>> rapl_hw_unit[0] is rapl_hw_unit[PERF_RAPL_PP0] rather than
>>> rapl_hw_unit[PERF_RAPL_PER_CORE]
>>>
>>> you cannot use rapl_hw_unit[i] to represent per-core rapl domain
>>> unit.
>>
>> Yes right, I saw that all the elements in the rapl_hw_unit array were
>> actually
>> using the value from the same register "MSR_RAPL_POWER_UNIT" or
>> "MSR_AMD_RAPL_POWER_UNIT".
>> Except for the two quirks,
>>
>> 737 case
>> RAPL_UNIT_QUIRK_INTEL_HSW:
>>
>>
>> 738 rapl_hw_unit[PERF_RAPL_RAM] =
>> 16;
>>
>>
>> 739
>> break;
>>
>>
>> 740 /* SPR uses a fixed energy unit for Psys domain. */
>> 741 case RAPL_UNIT_QUIRK_INTEL_SPR:
>> 742 rapl_hw_unit[PERF_RAPL_PSYS] = 0;
>> 743 break;
>>
>> So, as for AMD systems the rapl_hw_unit[] elements will always have
>> the same value, I ended
>> up using the rapl_hw_unit[PERF_RAPL_PP0] for
>> rapl_hw_unit[PERF_RAPL_PER_CORE], but I do realize
>> it is quite hacky. So, better to do it cleanly and add a separate
>> array/variable for the core events.
>>
> yeah, that is much better.
>>
>
>>>
>>>>
>>>> static struct rapl_model model_amd_hygon = {
>>>> .pkg_events = BIT(PERF_RAPL_PKG),
>>>> + .core_events = BIT(PERF_RAPL_PER_CORE),
>>>> .msr_power_unit = MSR_AMD_RAPL_POWER_UNIT,
>>>> - .rapl_msrs = amd_rapl_pkg_msrs,
>>>> + .rapl_pkg_msrs = amd_rapl_pkg_msrs,
>>>> + .rapl_core_msrs = amd_rapl_core_msrs,
>>>> };
>>>>
>>>> static const struct x86_cpu_id rapl_model_match[] __initconst =
>>>> {
>>>> @@ -858,6 +957,11 @@ static int __init rapl_pmu_init(void)
>>>> {
>>>> const struct x86_cpu_id *id;
>>>> int ret;
>>>> + int nr_rapl_pmu = topology_max_packages() *
>>>> topology_max_dies_per_package();
>>>> + int nr_cores = topology_max_packages() *
>>>> topology_num_cores_per_package();
>>>
>>> I'd suggest either using two variables nr_pkgs/nr_cores, or reuse
>>> one
>>> variable nr_rapl_pmu for both pkg pmu and per-core pmu.
>>
>> I understand your point, but the problem with that is, there are
>> actually three scopes needed here
>>
>> Some Intel systems need a *die* scope for the rapl_pmus_pkg PMU
>> Some Intel systems and all AMD systems need a *package* scope for the
>> rapl_pmus_pkg PMU
>> And AMD systems need a *core* scope for the rapl_pmus_per_core PMU
>>
>> I think what we can do is three variables, nr_dies (for all Intel
>> systems as before),
>> nr_pkgs(for AMD systems rapl_pmus_pkg PMU)
>
> Not necessarily, we already uses rapl_pmus_pkg for intel systems,
> right?
Yes, but scope of rapl_pmus_pkg is actually *die* for some Intel systems
(Xeon Cascade Lake-AP to be specific), right?
Whereas, all AMD systems have pkg scope for power PMU.
>
>> and nr_cores(for rapl_pmus_per_core PMU)
>>
>> Sounds good?
>
> what about just one variable "count" and reuse it for every cases?
Sure that would be cleaner, albeit not that explicit, will make the change
in next version
>
>>
>>>
>>>> +
>>>> + if (rapl_pmu_is_pkg_scope())
>>>> + nr_rapl_pmu = topology_max_packages();
>>>>
>>>> id = x86_match_cpu(rapl_model_match);
>>>> if (!id)
>>>> @@ -865,17 +969,34 @@ static int __init rapl_pmu_init(void)
>>>>
>>>> rapl_model = (struct rapl_model *) id->driver_data;
>>>>
>>>> - rapl_pkg_cntr_mask = perf_msr_probe(rapl_model-
>>>>> rapl_msrs,
>>>> PERF_RAPL_PKG_EVENTS_MAX,
>>>> + rapl_pkg_cntr_mask = perf_msr_probe(rapl_model-
>>>>> rapl_pkg_msrs, PERF_RAPL_PKG_EVENTS_MAX,
>>>> false, (void *)
>>>> &rapl_model-
>>>>> pkg_events);
>>>>
>>>> ret = rapl_check_hw_unit();
>>>> if (ret)
>>>> return ret;
>>>>
>>>> - ret = init_rapl_pmus(&rapl_pmus_pkg);
>>>> + ret = init_rapl_pmus(&rapl_pmus_pkg, nr_rapl_pmu,
>>>> rapl_attr_groups, rapl_attr_update);
>>>> if (ret)
>>>> return ret;
>>>>
>>>> + if (rapl_model->core_events) {
>>>> + rapl_core_cntr_mask = perf_msr_probe(rapl_model-
>>>>> rapl_core_msrs,
>>>> +
>>>> PERF_RAPL_CORE_EVENTS_MAX, false,
>>>> + (void *)
>>>> &rapl_model->core_events);
>>>> +
>>>> + ret = init_rapl_pmus(&rapl_pmus_core, nr_cores,
>>>> + rapl_per_core_attr_groups,
>>>> rapl_per_core_attr_update);
>>>> + if (ret) {
>>>> + /*
>>>> + * If initialization of per_core PMU
>>>> fails,
>>>> reset per_core
>>>> + * flag, and continue with power PMU
>>>> initialization.
>>>> + */
>>>> + pr_warn("Per-core PMU initialization
>>>> failed
>>>> (%d)\n", ret);
>>>> + rapl_model->core_events = 0UL;
>>>> + }
>>>> + }
>>>> +
>>>> /*
>>>> * Install callbacks. Core will call them for each online
>>>> cpu.
>>>> */
>>>> @@ -889,6 +1010,20 @@ static int __init rapl_pmu_init(void)
>>>> if (ret)
>>>> goto out1;
>>>>
>>>> + if (rapl_model->core_events) {
>>>> + ret = perf_pmu_register(&rapl_pmus_core->pmu,
>>>> "power_per_core", -1);
>>>> + if (ret) {
>>>> + /*
>>>> + * If registration of per_core PMU fails,
>>>> cleanup per_core PMU
>>>> + * variables, reset the per_core flag and
>>>> keep the
>>>> + * power PMU untouched.
>>>> + */
>>>> + pr_warn("Per-core PMU registration failed
>>>> (%d)\n", ret);
>>>> + cleanup_rapl_pmus(rapl_pmus_core);
>>>> + rapl_model->core_events = 0UL;
>>>> + }
>>>> + }
>>>> +
>>>> rapl_advertise();
>>>> return 0;
>>>>
>>>> @@ -906,5 +1041,9 @@ static void __exit intel_rapl_exit(void)
>>>> cpuhp_remove_state_nocalls(CPUHP_AP_PERF_X86_RAPL_ONLINE)
>>>> ;
>>>> perf_pmu_unregister(&rapl_pmus_pkg->pmu);
>>>> cleanup_rapl_pmus(rapl_pmus_pkg);
>>>> + if (rapl_model->core_events) {
>>>> + perf_pmu_unregister(&rapl_pmus_core->pmu);
>>>> + cleanup_rapl_pmus(rapl_pmus_core);
>>>> + }
>>>
>>> we do check rapl_pmus_core before accessing it, but we never check
>>> rapl_pmus_pkg because the previous code assumes it always exists.
>>>
>>> so could there be a problem if some one starts the per-core pmu
>>> when
>>> pkg pmu is unregistered and cleaned up?
>>>
>>> say, in rapl_pmu_event_init(),
>>>
>>> if (event->attr.type == rapl_pmus_pkg->pmu.type ||
>>> (rapl_pmus_core && event->attr.type == rapl_pmus_core-
>>>> pmu.type))
>>>
>>> this can break because rapl_pmus_pkg is freed, right?
>>
>> Hmm, I think this situation can't arise as whenever the power PMU
>> fails, we
>> directly go to the failure path and dont setup the per-core PMU(which
>> means
>> no one will be able to start the per-core PMU),
>> Please let me know if there is a scenario where this assumption can
>> fail.
>
> I mean if we do module unload and access power-per-core pmu at the same
> time, could there be a race?
>
> why not just unregister and cleanup the per-core pmu before the pkg
> pmu?
Yes, better to be safe, will reorder the cleanup.
Thanks,
Dhananjay
>>
>
> thanks,
> rui
>
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