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

[Liang, Kan]

On 2022-09-22 2:00 p.m., Dongli Zhang wrote:
> 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?

Yes, I will send it out shortly.


Thanks,
Kan
> 
> 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
>>