Re: [Patch v5 12/18] x86: pmu: Improve instruction and branches events verification

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

On 7/4/2024 4:02 PM, Sandipan Das wrote:
> On 7/3/2024 3:27 PM, 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 | 31 +++++++++++++++++++++++++++++++
>>  1 file changed, 31 insertions(+)
>>
>> diff --git a/x86/pmu.c b/x86/pmu.c
>> index d005e376..ffb7b4a4 100644
>> --- a/x86/pmu.c
>> +++ b/x86/pmu.c
>> @@ -19,6 +19,11 @@
>>  #define EXPECTED_INSTR 17
>>  #define EXPECTED_BRNCH 5
>>  
>> +
>> +/* Enable GLOBAL_CTRL + disable GLOBAL_CTRL instructions */
>> +#define EXTRA_INSTRNS  (3 + 3)
>> +#define LOOP_INSTRNS   (N * 10 + EXTRA_INSTRNS)
>> +#define LOOP_BRANCHES  (N)
>>  #define LOOP_ASM(_wrmsr)						\
>>  	_wrmsr "\n\t"							\
>>  	"mov %%ecx, %%edi; mov %%ebx, %%ecx;\n\t"			\
>> @@ -122,6 +127,24 @@ static inline void loop(u64 cntrs)
>>  		__precise_loop(cntrs);
>>  }
>>  
>> +static void adjust_events_range(struct pmu_event *gp_events,
>> +				int instruction_idx, int branch_idx)
>> +{
>> +	/*
>> +	 * If HW supports GLOBAL_CTRL MSR, enabling and disabling PMCs are
>> +	 * moved in __precise_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()) {
> This causes some intermittent failures on AMD processors using PerfMonV2
> due to variance in counts. This probably has to do with the way instructions
> leading to a VM-Entry or VM-Exit are accounted when counting retired
> instructions and branches. Adding the following change makes all the tests
> pass again.

Thanks to verify on AMD platforms. Would add it in next version.


>
> diff --git a/x86/pmu.c b/x86/pmu.c
> index 0658a1c1..09a34a3f 100644
> --- a/x86/pmu.c
> +++ b/x86/pmu.c
> @@ -222,7 +222,7 @@ static void adjust_events_range(struct pmu_event *gp_events,
>          * moved in __precise_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()) {
> +       if (pmu.is_intel && this_cpu_has_perf_global_ctrl()) {
>                 /* instructions event */
>                 gp_events[instruction_idx].min = LOOP_INSTRNS;
>                 gp_events[instruction_idx].max = LOOP_INSTRNS;
>
>
>> +		/* instructions event */
>> +		gp_events[instruction_idx].min = LOOP_INSTRNS;
>> +		gp_events[instruction_idx].max = LOOP_INSTRNS;
>> +		/* branches event */
>> +		gp_events[branch_idx].min = LOOP_BRANCHES;
>> +		gp_events[branch_idx].max = LOOP_BRANCHES;
>> +	}
>> +}
>> +
>>  volatile uint64_t irq_received;
>>  
>>  static void cnt_overflow(isr_regs_t *regs)
>> @@ -823,6 +846,9 @@ static void check_invalid_rdpmc_gp(void)
>>  
>>  int main(int ac, char **av)
>>  {
>> +	int instruction_idx;
>> +	int branch_idx;
>> +
>>  	setup_vm();
>>  	handle_irq(PMI_VECTOR, cnt_overflow);
>>  	buf = malloc(N*64);
>> @@ -836,13 +862,18 @@ 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]);
>> +		instruction_idx = INTEL_INSTRUCTIONS_IDX;
>> +		branch_idx = INTEL_BRANCHES_IDX;
>>  		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;
>> +		instruction_idx = AMD_INSTRUCTIONS_IDX;
>> +		branch_idx = AMD_BRANCHES_IDX;
>>  		report_prefix_push("AMD");
>>  	}
>> +	adjust_events_range(gp_events, instruction_idx, branch_idx);
>>  
>>  	printf("PMU version:         %d\n", pmu.version);
>>  	printf("GP counters:         %d\n", pmu.nr_gp_counters);
>