linux-kernel - Re: [PATCH V2 16/25] perf/x86: Register hybrid PMUs

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Date:   Thu, 11 Mar 2021 13:34:29 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...ux.intel.com
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
Subject: Re: [PATCH V2 16/25] perf/x86: Register hybrid PMUs

On Wed, Mar 10, 2021 at 08:37:52AM -0800, kan.liang@...ux.intel.com wrote:
> @@ -2092,9 +2105,37 @@ 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_hybrid_cpu_type(smp_processor_id());
> +		struct x86_hybrid_pmu *hybrid_pmu;
> +		int i;
> +
> +		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;
> +
> +			/* Only register the PMU for the boot CPU */

Why ?!

AFAICT we could register them all here. That instantly fixes that
CPU_STARTING / CPU_DEAD fail elsewhere in this patch.

> +			if (hybrid_pmu->cpu_type != cpu_type)
> +				continue;
> +
> +			err = perf_pmu_register(&hybrid_pmu->pmu, hybrid_pmu->name,
> +						x86_get_hybrid_pmu_type(cpu_type));
> +			if (err) {
> +				pr_warn("Failed to register a PMU, err %d\n", err);
> +				kfree(x86_pmu.hybrid_pmu);
> +				x86_pmu.hybrid_pmu = NULL;
> +				goto out2;
> +			}
> +		}
> +	}
>  
>  	return 0;
>