linux-kernel - Re: [RESEND PATCH 05/12] perf/x86: Add config

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Date: Fri, 21 Jun 2024 14:34:35 -0400
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...nel.org, acme@...nel.org, namhyung@...nel.org,
 irogers@...gle.com, adrian.hunter@...el.com,
 alexander.shishkin@...ux.intel.com, linux-kernel@...r.kernel.org,
 ak@...ux.intel.com, eranian@...gle.com,
 Dapeng Mi <dapeng1.mi@...ux.intel.com>
Subject: Re: [RESEND PATCH 05/12] perf/x86: Add config_mask to represent
 EVENTSEL bitmask



On 2024-06-20 12:16 p.m., Liang, Kan wrote:
> 
> 
> On 2024-06-20 3:44 a.m., Peter Zijlstra wrote:
>> On Tue, Jun 18, 2024 at 08:10:37AM -0700, kan.liang@...ux.intel.com wrote:
>>> From: Kan Liang <kan.liang@...ux.intel.com>
>>>
>>> Different vendors may support different fields in EVENTSEL MSR, such as
>>> Intel would introduce new fields umask2 and eq bits in EVENTSEL MSR
>>> since Perfmon version 6. However, a fixed mask X86_RAW_EVENT_MASK is
>>> used to filter the attr.config.
>>>
>>
>>> @@ -1231,6 +1233,11 @@ static inline int x86_pmu_num_counters_fixed(struct pmu *pmu)
>>>  	return hweight64(hybrid(pmu, fixed_cntr_mask64));
>>>  }
>>>  
>>> +static inline u64 x86_pmu_get_event_config(struct perf_event *event)
>>> +{
>>> +	return event->attr.config & hybrid(event->pmu, config_mask);
>>> +}
>>
>> Seriously, we're going to be having such major event encoding
>> differences between cores on a single chip?
> 
> For LNL, no. But ARL-H may have an event encoding differences.
> I will double check.

There are two generations of e-core on ARL-H. The event encoding is
different.

The new fields umask2 and eq bits are enumerated by CPUID.(EAX=23H,
ECX=0H):EBX. They are supported by CPU 11 but not CPU 12.

CPU 11:
   0x00000023 0x00: eax=0x0000000f ebx=0x00000003 ecx=0x00000008
edx=0x00000000
CPU 12:
   0x00000023 0x00: eax=0x0000000b ebx=0x00000000 ecx=0x00000006
edx=0x00000000


Thanks,
Kan
> 
> The problem is that there is no guarantee for the future platforms.
> With the CPUID leaf 0x23, all the features are enumerated per CPU.
> In theory, it's possible that different layout of the EVENTSEL MSR
> between different types of core.
> If we take the virtualization into account, that's even worse.
> 
> It should be a safe way to add the hybrid() check.
> 
> 
> Thanks,
> Kan
>