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

Peter Zijlstra
2020-05-19T10:45:36Z

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.