linux-kernel - Re: [PATCH V5 16/25] perf/x86: Register hybrid PMUs

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Date:   Fri, 9 Apr 2021 09:50:20 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, acme@...nel.org,
        tglx@...utronix.de, bp@...en8.de, namhyung@...nel.org,
        jolsa@...hat.com, ak@...ux.intel.com, yao.jin@...ux.intel.com,
        alexander.shishkin@...ux.intel.com, adrian.hunter@...el.com,
        ricardo.neri-calderon@...ux.intel.com
Subject: Re: [PATCH V5 16/25] perf/x86: Register hybrid PMUs



On 4/9/2021 2:58 AM, Peter Zijlstra wrote:
> On Mon, Apr 05, 2021 at 08:10:58AM -0700, kan.liang@...ux.intel.com wrote:
>> @@ -2089,9 +2119,46 @@ static int __init init_hw_perf_events(void)
>>   	if (err)
>>   		goto out1;
>>   
>> -	err = perf_pmu_register(&pmu, "cpu", PERF_TYPE_RAW);
>> -	if (err)
>> -		goto out2;
>> +	if (!is_hybrid()) {
>> +		err = perf_pmu_register(&pmu, "cpu", PERF_TYPE_RAW);
>> +		if (err)
>> +			goto out2;
>> +	} else {
>> +		u8 cpu_type = get_this_hybrid_cpu_type();
>> +		struct x86_hybrid_pmu *hybrid_pmu;
>> +		bool registered = false;
>> +		int i;
>> +
>> +		if (!cpu_type && x86_pmu.get_hybrid_cpu_type)
>> +			cpu_type = x86_pmu.get_hybrid_cpu_type();
>> +
>> +		for (i = 0; i < x86_pmu.num_hybrid_pmus; i++) {
>> +			hybrid_pmu = &x86_pmu.hybrid_pmu[i];
>> +
>> +			hybrid_pmu->pmu = pmu;
>> +			hybrid_pmu->pmu.type = -1;
>> +			hybrid_pmu->pmu.attr_update = x86_pmu.attr_update;
>> +			hybrid_pmu->pmu.capabilities |= PERF_PMU_CAP_HETEROGENEOUS_CPUS;
>> +
>> +			err = perf_pmu_register(&hybrid_pmu->pmu, hybrid_pmu->name,
>> +						(hybrid_pmu->cpu_type == hybrid_big) ? PERF_TYPE_RAW : -1);
>> +			if (err)
>> +				continue;
>> +
>> +			if (cpu_type == hybrid_pmu->cpu_type)
>> +				x86_pmu_update_cpu_context(&hybrid_pmu->pmu, raw_smp_processor_id());
>> +
>> +			registered = true;
>> +		}
>> +
>> +		if (!registered) {
>> +			pr_warn("Failed to register hybrid PMUs\n");
>> +			kfree(x86_pmu.hybrid_pmu);
>> +			x86_pmu.hybrid_pmu = NULL;
>> +			x86_pmu.num_hybrid_pmus = 0;
>> +			goto out2;
>> +		}
> 
> I don't think this is quite right. registered will be true even if one
> fails, while I think you meant to only have it true when all (both)
> types registered correctly.

No, I mean that perf error out only when all types fail to be registered.

For the case (1 failure, 1 success), users can still access the 
registered PMU.
When a CPU belongs to the unregistered PMU online, a warning will be 
displayed. Because in init_hybrid_pmu(), we will check the PMU type 
before update the CPU mask.

         if (WARN_ON_ONCE(!pmu || (pmu->pmu.type == -1))) {
                 cpuc->pmu = NULL;
                 return false;
         }


Thanks,
Kan