Re: [PATCH RFC 1/1] perf stat: do not fatal if the leader is errored

[Dongli Zhang]

Hi Kan,

I have tested that the patch works by hiding 'slots' sysfs entries.

# ll /sys/bus/event_source/devices/cpu/events/
total 0
-r--r--r--. 1 root root 4096 Sep 22 17:57 branch-instructions
-r--r--r--. 1 root root 4096 Sep 22 17:57 branch-misses
-r--r--r--. 1 root root 4096 Sep 22 17:57 bus-cycles
-r--r--r--. 1 root root 4096 Sep 22 17:57 cache-misses
-r--r--r--. 1 root root 4096 Sep 22 17:57 cache-references
-r--r--r--. 1 root root 4096 Sep 22 17:57 cpu-cycles
-r--r--r--. 1 root root 4096 Sep 22 17:57 instructions
-r--r--r--. 1 root root 4096 Sep 22 17:57 ref-cycles

# perf stat
^C
 Performance counter stats for 'system wide':

         19,256.20 msec cpu-clock                        #   16.025 CPUs
utilized
               179      context-switches                 #    9.296 /sec

                17      cpu-migrations                   #    0.883 /sec

                 3      page-faults                      #    0.156 /sec

         7,502,294      cycles                           #    0.000 GHz

         2,512,587      instructions                     #    0.33  insn per
cycle
           552,989      branches                         #   28.717 K/sec

            15,999      branch-misses                    #    2.89% of all
branches

       1.201628129 seconds time elapsed


Would you send this patch to fix at the kernel side?

Thank you very much!

Dongli Zhang

On 9/22/22 6:34 AM, Liang, Kan wrote:
> 
> 
> On 2022-09-22 4:07 a.m., Like Xu wrote:
>> On 22/9/2022 3:10 pm, Dongli Zhang wrote:
>>> There are three options to fix the issue.
>>>
>>> 1. Do not expose /sys/bus/event_source/devices/cpu/events/slots to
>>> userspace so that pmu_have_event(pmu->name, "slots") returns false.
>>
>> IMO, the guest PMU driver should be fixed
>> since it misrepresents emulated hardware capabilities in terms of slots.
> 
> Yes, we need to fix the kernel to hide the slots event if it's not
> available.
> 
> The patch as below should fix it. (Not tested yet)
> 
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index b20e646c8205..27ee43faba32 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -5565,6 +5565,19 @@ static struct attribute *intel_pmu_attrs[] = {
>  	NULL,
>  };
> 
> +static umode_t
> +td_is_visible(struct kobject *kobj, struct attribute *attr, int i)
> +{
> +	/*
> +	 * Hide the perf metrics topdown events
> +	 * if the slots is not in CPUID.
> +	 */
> +	if (x86_pmu.num_topdown_events)
> +		return (x86_pmu.intel_ctrl & INTEL_PMC_MSK_FIXED_SLOTS) ? attr->mode : 0;
> +
> +	return attr->mode;
> +}
> +
>  static umode_t
>  tsx_is_visible(struct kobject *kobj, struct attribute *attr, int i)
>  {
> @@ -5600,6 +5613,7 @@ default_is_visible(struct kobject *kobj, struct
> attribute *attr, int i)
> 
>  static struct attribute_group group_events_td  = {
>  	.name = "events",
> +	.is_visible = td_is_visible,
>  };
> 
>  static struct attribute_group group_events_mem = {
> @@ -5758,6 +5772,23 @@ static inline int
> hybrid_find_supported_cpu(struct x86_hybrid_pmu *pmu)
>  	return (cpu >= nr_cpu_ids) ? -1 : cpu;
>  }
> 
> +static umode_t hybrid_td_is_visible(struct kobject *kobj,
> +					struct attribute *attr, int i)
> +{
> +	struct device *dev = kobj_to_dev(kobj);
> +	struct x86_hybrid_pmu *pmu =
> +		 container_of(dev_get_drvdata(dev), struct x86_hybrid_pmu, pmu);
> +
> +	if (!is_attr_for_this_pmu(kobj, attr))
> +		return 0;
> +
> +	/* Only check the big core which supports perf metrics */
> +	if (pmu->cpu_type == hybrid_big)
> +		return (pmu->intel_ctrl & INTEL_PMC_MSK_FIXED_SLOTS) ? attr->mode : 0;
> +
> +	return attr->mode;
> +}
> +
>  static umode_t hybrid_tsx_is_visible(struct kobject *kobj,
>  				     struct attribute *attr, int i)
>  {
> @@ -5784,7 +5815,7 @@ static umode_t hybrid_format_is_visible(struct
> kobject *kobj,
> 
>  static struct attribute_group hybrid_group_events_td  = {
>  	.name		= "events",
> -	.is_visible	= hybrid_events_is_visible,
> +	.is_visible	= hybrid_td_is_visible,
>  };
> 
>  static struct attribute_group hybrid_group_events_mem = {
> 
> 
> Thanks,
> Kan
>