linux-kernel - Re: [kvm-unit-tests PATCH 2/2] x86/pmu: Add AMD Guest PerfMonV2 testcases

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Message-ID: <6b852e8d-39f1-4baf-74f5-f98dd9f4e371@gmail.com>
Date:   Wed, 19 Oct 2022 17:40:44 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sandipan Das <sandipan.das@....com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [kvm-unit-tests PATCH 2/2] x86/pmu: Add AMD Guest PerfMonV2
 testcases

All applied, thanks.

On 6/10/2022 6:08 am, Sean Christopherson wrote:
> Can you provide a single series for all of the KVM-Unit-Tests PMU work (separate
> from the KVM patches)?  Ya, it'll be big and is a blatant violation of "do one
> thing", but trying to manually handle the dependencies on the review side is time
> consuming.

Thanks for your time. PMU test cases will be combined, if no new ideas emerge.

> 
> One thought to help keep track of dependencies between KVM and KUT would be to
> add dummy commits between each sub-series, with the dummy commit containing a lore
> link to the relevant KVM patches/series.  That would allow throwing everything into
> one series without losing track of things.  Hopefully.

Sure, adding a lore link to a cover letter is always helpful. It seems that the 
ageing KVM project
has moved to a test-driven approach to development, and any new developer should 
be aware
of this rule.

> 
> On Mon, Sep 05, 2022, Like Xu wrote:
>> diff --git a/lib/x86/processor.h b/lib/x86/processor.h
>> index 9c490d9..b9592c4 100644
>> --- a/lib/x86/processor.h
>> +++ b/lib/x86/processor.h
>> @@ -796,8 +796,12 @@ static inline void flush_tlb(void)
>>   
>>   static inline u8 pmu_version(void)
>>   {
>> -	if (!is_intel())
>> +	if (!is_intel()) {
>> +		/* Performance Monitoring Version 2 Supported */
>> +		if (cpuid(0x80000022).a & 0x1)
> 
> Add an X86_FEATURE_*, that way this is self-documenting.
> 
>> +			return 2;
>>   		return 0;
>> +	}
>>   
>>   	return cpuid(10).a & 0xff;
>>   }
>> @@ -824,6 +828,9 @@ static inline u8 pmu_nr_gp_counters(void)
>>   {
>>   	if (is_intel()) {
>>   		return (cpuid(10).a >> 8) & 0xff;
>> +	} else if (this_cpu_has_perf_global_ctrl()) {
> 
> Eww.  Took me too long to connect the dots to understand how this guarantees that
> leaf 0x80000022 is available.  With an X86_FEATURE_* this can simply be:
> 
> 	} else if (this_cpu_has(X86_FEATURE_AMD_PMU_V2) {
> 
> or whatever name is appropriate.
> 
>> +		/* Number of Core Performance Counters. */
>> +		return cpuid(0x80000022).b & 0xf;
>>   	} else if (!has_amd_perfctr_core()) {
>>   		return AMD64_NUM_COUNTERS;
>>   	}
>> diff --git a/x86/pmu.c b/x86/pmu.c
>> index 11607c0..6d5363b 100644
>> --- a/x86/pmu.c
>> +++ b/x86/pmu.c
>> @@ -72,6 +72,9 @@ struct pmu_event {
>>   #define PMU_CAP_FW_WRITES	(1ULL << 13)
>>   static u32 gp_counter_base;
>>   static u32 gp_select_base;
>> +static u32 global_status_msr;
>> +static u32 global_ctl_msr;
>> +static u32 global_status_clr_msr;
> 
> What do you think about naming these like MSR #defines?  E.g.
> 
>    MSR_PERF_GLOBAL_CTRL
>    MSR_PERF_GLOBAL_STATUS
>    MSR_PERF_GLOBAL_STATUS_CLR
> 
> There's a little risk of causing confusing, but I think it would make the code
> easier to read.

Lowercase variable names are applied.

> 
>>   static unsigned int gp_events_size;
>>   static unsigned int nr_gp_counters;
>>   
>> @@ -150,8 +153,7 @@ static void global_enable(pmu_counter_t *cnt)
>>   		return;
>>   
>>   	cnt->idx = event_to_global_idx(cnt);
>> -	wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, rdmsr(MSR_CORE_PERF_GLOBAL_CTRL) |
>> -			(1ull << cnt->idx));
>> +	wrmsr(global_ctl_msr, rdmsr(global_ctl_msr) | (1ull << cnt->idx));
> 
> Opportunistically use BIT_ULL().
> 
>>   }
>>   
>>   static void global_disable(pmu_counter_t *cnt)
>> @@ -159,8 +161,7 @@ static void global_disable(pmu_counter_t *cnt)
>>   	if (pmu_version() < 2)
>>   		return;
>>   
>> -	wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, rdmsr(MSR_CORE_PERF_GLOBAL_CTRL) &
>> -			~(1ull << cnt->idx));
>> +	wrmsr(global_ctl_msr, rdmsr(global_ctl_msr) & ~(1ull << cnt->idx));
> 
> BIT_ULL()
> 
>>   }
>>   
>>   static inline uint32_t get_gp_counter_msr(unsigned int i)
>> @@ -326,6 +327,23 @@ static void check_counters_many(void)
>>   	report(i == n, "all counters");
>>   }
>>   
>> +static bool is_the_count_reproducible(pmu_counter_t *cnt)
>> +{
>> +	unsigned int i;
>> +	uint64_t count;
>> +
>> +	__measure(cnt, 0);
>> +	count = cnt->count;
>> +
>> +	for (i = 0; i < 10; i++) {
>> +		__measure(cnt, 0);
>> +		if (count != cnt->count)
>> +			return false;
>> +	}
>> +
>> +	return true;
>> +}
>> +
>>   static void check_counter_overflow(void)
>>   {
>>   	uint64_t count;
>> @@ -334,13 +352,14 @@ static void check_counter_overflow(void)
>>   		.ctr = gp_counter_base,
>>   		.config = EVNTSEL_OS | EVNTSEL_USR | (*gp_events)[1].unit_sel /* instructions */,
>>   	};
>> +	bool precise_event = is_the_count_reproducible(&cnt);
>> +
>>   	__measure(&cnt, 0);
>>   	count = cnt.count;
>>   
>>   	/* clear status before test */
>>   	if (pmu_version() > 1) {
> 
> Please provide helper(s) to replace the myriad open coded "pmu_version() > ???"
> checks.  E.g. this one appears to be:
> 
> 	if (this_cpu_has_perf_global_status_clr())
> 
> I obviously don't care about the verbosity, it's that people like me might not
> know what the PMU version has to do with an MSR being accessible.