linux-kernel - Re: [PATCH v2 2/7] perf/x86/core: Remove unnecessary stubs provided for KVM-only helpers

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Date:   Thu, 4 Aug 2022 15:07:43 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Like Xu <like.xu.linux@...il.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH v2 2/7] perf/x86/core: Remove unnecessary stubs provided
 for KVM-only helpers

On Thu, Aug 04, 2022, Like Xu wrote:
> On 4/8/2022 3:26 am, Sean Christopherson wrote:
> > -#if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_CPU_SUP_AMD)
> > - extern void amd_pmu_enable_virt(void);
> > - extern void amd_pmu_disable_virt(void);
> > -
> > -#if defined(CONFIG_PERF_EVENTS_AMD_BRS)
> > +#ifdef CONFIG_PERF_EVENTS_AMD_BRS
> >   #define PERF_NEEDS_LOPWR_CB 1
> > @@ -566,12 +538,13 @@ static inline void perf_lopwr_cb(bool lopwr_in)
> >   	static_call_mod(perf_lopwr_cb)(lopwr_in);
> >   }
> > -#endif /* PERF_NEEDS_LOPWR_CB */
> 
> Oops, now the definition of PERF_NEEDS_LOPWR_CB will not be unset.
> This is not mentioned in the commit message and may cause trouble.

PERF_NEEDS_LOPWR_CB isn't being "unset" in the existing code, the comment is simply
wrong.  The #endif pairs with CONFIG_PERF_EVENTS_AMD_BRS.

  #if defined(CONFIG_PERF_EVENTS_AMD_BRS)

  #define PERF_NEEDS_LOPWR_CB 1

  /*
   * architectural low power callback impacts
   * drivers/acpi/processor_idle.c
   * drivers/acpi/acpi_pad.c
   */
  extern void perf_amd_brs_lopwr_cb(bool lopwr_in);

  DECLARE_STATIC_CALL(perf_lopwr_cb, perf_amd_brs_lopwr_cb);

  static inline void perf_lopwr_cb(bool lopwr_in)
  {
  	static_call_mod(perf_lopwr_cb)(lopwr_in);
  }

  #endif /* PERF_NEEDS_LOPWR_CB */ <=== should be /* CONFIG_PERF_EVENTS_AMD_BRS */