linux-kernel - Re: [PATCH v2 1/8] perf/x86: add a function to get the lbr stack

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Message-ID: <5B921E84.4010008@intel.com>
Date:   Fri, 07 Sep 2018 14:45:24 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     Andi Kleen <ak@...ux.intel.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Liang, Kan" <kan.liang@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "Xu, Like" <like.xu@...el.com>
Subject: Re: [PATCH v2 1/8] perf/x86: add a function to get the lbr stack

On 09/07/2018 11:28 AM, Andi Kleen wrote:
>> +int perf_get_lbr_stack(struct perf_lbr_stack *stack)
>> +{
>> +	stack->lbr_nr = x86_pmu.lbr_nr;
>> +	stack->lbr_tos = x86_pmu.lbr_tos;
>> +	stack->lbr_from = x86_pmu.lbr_from;
>> +	stack->lbr_to = x86_pmu.lbr_to;
>> +
>> +	if (x86_pmu.intel_cap.lbr_format == LBR_FORMAT_INFO)
>> +		stack->lbr_info = MSR_LBR_INFO_0;
>> +	else
>> +		stack->lbr_info = 0;
> Seems weird to export the enum value if the enum isn't exported.
> How can it be used?
>

I'm not sure about the issue. The caller gets the value of 
MSR_LBR_INFO_0 (not the enum, LBR_FORMAT_INFO) only when the hardware 
supports it. If hardware doesn't support it, just sets it to 0, and 
there will be no lbr info msr to be passed through.

Best,
Wei