linux-kernel - Re: [PATCH 5/7] perf/x86/amd/core: Add PerfMonV2 counter control

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Date:   Fri, 18 Mar 2022 13:32:04 +0530
From:   Sandipan Das <sandipan.das@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        x86@...nel.org, bp@...en8.de, dave.hansen@...ux.intel.com,
        acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, namhyung@...nel.org,
        jolsa@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        pbonzini@...hat.com, jmattson@...gle.com, like.xu.linux@...il.com,
        eranian@...gle.com, ananth.narayan@....com, ravi.bangoria@....com,
        santosh.shukla@....com
Subject: Re: [PATCH 5/7] perf/x86/amd/core: Add PerfMonV2 counter control


On 3/17/2022 5:16 PM, Peter Zijlstra wrote:
> On Thu, Mar 17, 2022 at 11:58:34AM +0530, Sandipan Das wrote:
>> @@ -625,12 +630,32 @@ static void amd_pmu_wait_on_overflow(int idx)
>>  	}
>>  }
>>  
>> +static void amd_pmu_global_enable_all(int added)
>> +{
>> +	amd_pmu_set_global_ctl(amd_pmu_global_cntr_mask);
>> +}
>> +
>> +DEFINE_STATIC_CALL(amd_pmu_enable_all, x86_pmu_enable_all);
>> +
>> +static void amd_pmu_enable_all(int added)
>> +{
>> +	static_call(amd_pmu_enable_all)(added);
>> +}
>> +
>> +static void amd_pmu_global_disable_all(void)
>> +{
>> +	/* Disable all PMCs */
>> +	amd_pmu_set_global_ctl(0);
>> +}
>> +
>> +DEFINE_STATIC_CALL(amd_pmu_disable_all, x86_pmu_disable_all);
>> +
>>  static void amd_pmu_disable_all(void)
>>  {
>>  	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
>>  	int idx;
>>  
>> -	x86_pmu_disable_all();
>> +	static_call(amd_pmu_disable_all)();
>>  
>>  	/*
>>  	 * This shouldn't be called from NMI context, but add a safeguard here
>> @@ -671,6 +696,28 @@ static void amd_pmu_disable_event(struct perf_event *event)
>>  	amd_pmu_wait_on_overflow(event->hw.idx);
>>  }
>>  
>> +static void amd_pmu_global_enable_event(struct perf_event *event)
>> +{
>> +	struct hw_perf_event *hwc = &event->hw;
>> +
>> +	/*
>> +	 * Testing cpu_hw_events.enabled should be skipped in this case unlike
>> +	 * in x86_pmu_enable_event().
>> +	 *
>> +	 * Since cpu_hw_events.enabled is set only after returning from
>> +	 * x86_pmu_start(), the PMCs must be programmed and kept ready.
>> +	 * Counting starts only after x86_pmu_enable_all() is called.
>> +	 */
>> +	__x86_pmu_enable_event(hwc, ARCH_PERFMON_EVENTSEL_ENABLE);
>> +}
>> +
>> +DEFINE_STATIC_CALL(amd_pmu_enable_event, x86_pmu_enable_event);
>> +
>> +static void amd_pmu_enable_event(struct perf_event *event)
>> +{
>> +	static_call(amd_pmu_enable_event)(event);
>> +}
>> +
>>  /*
>>   * Because of NMI latency, if multiple PMC counters are active or other sources
>>   * of NMIs are received, the perf NMI handler can handle one or more overflowed
>> @@ -929,8 +976,8 @@ static __initconst const struct x86_pmu amd_pmu = {
>>  	.name			= "AMD",
>>  	.handle_irq		= amd_pmu_handle_irq,
>>  	.disable_all		= amd_pmu_disable_all,
>> -	.enable_all		= x86_pmu_enable_all,
>> -	.enable			= x86_pmu_enable_event,
>> +	.enable_all		= amd_pmu_enable_all,
>> +	.enable			= amd_pmu_enable_event,
>>  	.disable		= amd_pmu_disable_event,
>>  	.hw_config		= amd_pmu_hw_config,
>>  	.schedule_events	= x86_schedule_events,
>> @@ -989,6 +1036,11 @@ static int __init amd_core_pmu_init(void)
>>  		x86_pmu.num_counters = EXT_PERFMON_DEBUG_NUM_CORE_PMC(ebx);
>>  
>>  		amd_pmu_global_cntr_mask = (1ULL << x86_pmu.num_counters) - 1;
>> +
>> +		/* Update PMC handling functions */
>> +		static_call_update(amd_pmu_enable_all, amd_pmu_global_enable_all);
>> +		static_call_update(amd_pmu_disable_all, amd_pmu_global_disable_all);
>> +		static_call_update(amd_pmu_enable_event, amd_pmu_global_enable_event);
>>  	}
> 
> 
> This makes no sense to me...
> 
> First and foremost, *please* tell me your shiny new hardware fixed the
> terrible behaviour that requires the wait_on_overflow hacks in
> amd_pmu_disable_all().

Unfortunately, that workaround is still required.

> 
> Second, all these x86_pmu methods are already static_calls per
> arch/x86/events/core.c. So what you want to do is something like:
> 
> 	x86_pmu = amd_pmu;
> 	if (amd_v2) {
> 		x86_pmu.disable_all = amd_v2_disable_all;
> 		x86_pmu.enable_all  = amd_v2_enable_all;
> 	}
> 
> And leave it at that.
> 

Sure. I'll clean this up.

- Sandipan