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

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Message-ID: <YHB2mNgw7k/NUIl9@hirez.programming.kicks-ass.net>
Date:   Fri, 9 Apr 2021 17:45:28 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Liang, Kan" <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,
        ricardo.neri-calderon@...ux.intel.com
Subject: Re: [PATCH V5 16/25] perf/x86: Register hybrid PMUs

On Fri, Apr 09, 2021 at 09:50:20AM -0400, Liang, Kan wrote:
> 
> 
> 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.

All or nothing seems a better approach to me. There really isn't a good
reason for any one of them to fail.