linux-kernel - Re: [PATCH v11 05/11] perf/x86: Keep LBR stack unchanged in host context for guest LBR event

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Message-ID: <20200519104520.GE279861@hirez.programming.kicks-ass.net>
Date:   Tue, 19 May 2020 12:45:20 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Like Xu <like.xu@...ux.intel.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>, ak@...ux.intel.com,
        wei.w.wang@...el.com
Subject: Re: [PATCH v11 05/11] perf/x86: Keep LBR stack unchanged in host
 context for guest LBR event

On Tue, May 19, 2020 at 11:08:41AM +0800, Like Xu wrote:

> Sure, I could reuse cpuc->intel_ctrl_guest_mask to rewrite this part:
> 
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index d788edb7c1f9..f1243e8211ca 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -2189,7 +2189,8 @@ static void intel_pmu_disable_event(struct perf_event
> *event)
>         } else if (idx == INTEL_PMC_IDX_FIXED_BTS) {
>                 intel_pmu_disable_bts();
>                 intel_pmu_drain_bts_buffer();
> -       }
> +       } else if (idx == INTEL_PMC_IDX_FIXED_VLBR)
> +               intel_clear_masks(event, idx);
> 
>         /*
>          * Needs to be called after x86_pmu_disable_event,
> @@ -2271,7 +2272,8 @@ static void intel_pmu_enable_event(struct perf_event
> *event)
>                 if (!__this_cpu_read(cpu_hw_events.enabled))
>                         return;
>                 intel_pmu_enable_bts(hwc->config);
> -       }
> +       } else if (idx == INTEL_PMC_IDX_FIXED_VLBR)
> +               intel_set_masks(event, idx);
>  }

This makes me wonder if we can pull intel_{set,clear}_masks() out of
that if()-forest, but that's something for later...

>  static void intel_pmu_add_event(struct perf_event *event)
> diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
> index b8dabf1698d6..1b30c76815dd 100644
> --- a/arch/x86/events/intel/lbr.c
> +++ b/arch/x86/events/intel/lbr.c
> @@ -552,11 +552,19 @@ void intel_pmu_lbr_del(struct perf_event *event)
>         perf_sched_cb_dec(event->ctx->pmu);
>  }
> 
> +static inline bool vlbr_is_enabled(void)
> +{
> +       struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> +
> +       return test_bit(INTEL_PMC_IDX_FIXED_VLBR,
> +               (unsigned long *)&cpuc->intel_ctrl_guest_mask);
> +}

Maybe call this: vlbr_exclude_host() ?

> +
>  void intel_pmu_lbr_enable_all(bool pmi)
>  {
>         struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> 
> -       if (cpuc->lbr_users)
> +       if (cpuc->lbr_users && !vlbr_is_enabled())
>                 __intel_pmu_lbr_enable(pmi);
>  }
> 
> @@ -564,7 +572,7 @@ void intel_pmu_lbr_disable_all(void)
>  {
>         struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> 
> -       if (cpuc->lbr_users)
> +       if (cpuc->lbr_users && !vlbr_is_enabled())
>                 __intel_pmu_lbr_disable();
>  }
> 
> @@ -706,7 +714,8 @@ void intel_pmu_lbr_read(void)
>          * This could be smarter and actually check the event,
>          * but this simple approach seems to work for now.
>          */
> -       if (!cpuc->lbr_users || cpuc->lbr_users == cpuc->lbr_pebs_users)
> +       if (!cpuc->lbr_users || vlbr_is_enabled() ||
> +               cpuc->lbr_users == cpuc->lbr_pebs_users)
>                 return;
> 
>         if (x86_pmu.intel_cap.lbr_format == LBR_FORMAT_32)
> 
> Is this acceptable to you ?

Yeah, looks about right. Let me stare at the rest.