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

Like Xu
2020-05-19T03:08:50Z

Hi Peter,

Thanks for the clear attitude and code refinement.

On 2020/5/18 20:02, Peter Zijlstra wrote:
> On Thu, May 14, 2020 at 04:30:48PM +0800, Like Xu wrote:
>> @@ -544,7 +562,12 @@ void intel_pmu_lbr_enable_all(bool pmi)
>> {
>> struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
>>
>> - if (cpuc->lbr_users)
>> + /*
>> + * When the LBR hardware is scheduled for a guest LBR event,
>> + * the guest will dis/enables LBR itself at the appropriate time,
>> + * including configuring MSR_LBR_SELECT.
>> + */
>> + if (cpuc->lbr_users && !cpuc->guest_lbr_enabled)
>> __intel_pmu_lbr_enable(pmi);
>> }
>
> No!, that should be done through perf_event_attr::exclude_host, as I
> believe all the other KVM event do it.
>

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);
}

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);
+}
+
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 ?

If you have more comments on the patchset, please let me know.

Thanks,
Like Xu