Re: [kvm-unit-tests Patch v3 08/11] x86: pmu: Improve instruction and branches events verification

["Mi, Dapeng" <dapeng1.mi@linux.intel.com>]

On 3/27/2024 2:14 PM, Mingwei Zhang wrote:
> On Wed, Jan 03, 2024, Dapeng Mi wrote:
>> If HW supports GLOBAL_CTRL MSR, enabling and disabling PMCs are moved in
>> __precise_count_loop(). Thus, instructions and branches events can be
>> verified against a precise count instead of a rough range.
>>
>> Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
>> ---
>>   x86/pmu.c | 26 ++++++++++++++++++++++++++
>>   1 file changed, 26 insertions(+)
>>
>> diff --git a/x86/pmu.c b/x86/pmu.c
>> index 88b89ad889b9..b764827c1c3d 100644
>> --- a/x86/pmu.c
>> +++ b/x86/pmu.c
>> @@ -25,6 +25,10 @@
>>   	"nop; nop; nop; nop; nop; nop; nop;\n\t"	\
>>   	"loop 1b;\n\t"
>>   
>> +/*Enable GLOBAL_CTRL + disable GLOBAL_CTRL instructions */
>> +#define PRECISE_EXTRA_INSTRNS  (2 + 4)
>> +#define PRECISE_LOOP_INSTRNS   (N * LOOP_INSTRNS + PRECISE_EXTRA_INSTRNS)
>> +#define PRECISE_LOOP_BRANCHES  (N)
>>   #define PRECISE_LOOP_ASM						\
>>   	"wrmsr;\n\t"							\
>>   	"mov %%ecx, %%edi; mov %%ebx, %%ecx;\n\t"			\
>> @@ -107,6 +111,24 @@ static inline void loop(u64 cntrs)
>>   		__precise_count_loop(cntrs);
>>   }
>>   
>> +static void adjust_events_range(struct pmu_event *gp_events, int branch_idx)
>> +{
>> +	/*
>> +	 * If HW supports GLOBAL_CTRL MSR, enabling and disabling PMCs are
>> +	 * moved in __precise_count_loop(). Thus, instructions and branches
>> +	 * events can be verified against a precise count instead of a rough
>> +	 * range.
>> +	 */
>> +	if (this_cpu_has_perf_global_ctrl()) {
>> +		/* instructions event */
>> +		gp_events[0].min = PRECISE_LOOP_INSTRNS;
>> +		gp_events[0].max = PRECISE_LOOP_INSTRNS;
>> +		/* branches event */
>> +		gp_events[branch_idx].min = PRECISE_LOOP_BRANCHES;
>> +		gp_events[branch_idx].max = PRECISE_LOOP_BRANCHES;
>> +	}
>> +}
>> +
>>   volatile uint64_t irq_received;
>>   
>>   static void cnt_overflow(isr_regs_t *regs)
>> @@ -771,6 +793,7 @@ static void check_invalid_rdpmc_gp(void)
>>   
>>   int main(int ac, char **av)
>>   {
>> +	int branch_idx;
>>   	setup_vm();
>>   	handle_irq(PMI_VECTOR, cnt_overflow);
>>   	buf = malloc(N*64);
>> @@ -784,13 +807,16 @@ int main(int ac, char **av)
>>   		}
>>   		gp_events = (struct pmu_event *)intel_gp_events;
>>   		gp_events_size = sizeof(intel_gp_events)/sizeof(intel_gp_events[0]);
>> +		branch_idx = 5;
> This (and the follow up one) hardcoded index is hacky and more
> importantly, error prone especially when code get refactored later.
> Please use a proper way via macro? Eg., checking
> INTEL_ARCH_BRANCHES_RETIRED_INDEX in pmu_counters_test.c might be a good
> one.

Yeah, I would define an enum to enumerate these indexes. Thanks.


>>   		report_prefix_push("Intel");
>>   		set_ref_cycle_expectations();
>>   	} else {
>>   		gp_events_size = sizeof(amd_gp_events)/sizeof(amd_gp_events[0]);
>>   		gp_events = (struct pmu_event *)amd_gp_events;
>> +		branch_idx = 2;
>>   		report_prefix_push("AMD");
>>   	}
>> +	adjust_events_range(gp_events, branch_idx);
>>   
>>   	printf("PMU version:         %d\n", pmu.version);
>>   	printf("GP counters:         %d\n", pmu.nr_gp_counters);
>> -- 
>> 2.34.1
>>