Re: [kvm-unit-tests Patch v3 07/11] x86: pmu: Enable and disable PMCs in loop() asm blob

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

On 4/9/2024 7:17 AM, Mingwei Zhang wrote:
> On Wed, Mar 27, 2024, Mi, Dapeng wrote:
>> On 3/27/2024 2:07 PM, Mingwei Zhang wrote:
>>> On Wed, Jan 03, 2024, Dapeng Mi wrote:
>>>> Currently enabling PMCs, executing loop() and disabling PMCs are divided
>>>> 3 separated functions. So there could be other instructions executed
>>>> between enabling PMCS and running loop() or running loop() and disabling
>>>> PMCs, e.g. if there are multiple counters enabled in measure_many()
>>>> function, the instructions which enabling the 2nd and more counters
>>>> would be counted in by the 1st counter.
>>>>
>>>> So current implementation can only verify the correctness of count by an
>>>> rough range rather than a precise count even for instructions and
>>>> branches events. Strictly speaking, this verification is meaningless as
>>>> the test could still pass even though KVM vPMU has something wrong and
>>>> reports an incorrect instructions or branches count which is in the rough
>>>> range.
>>>>
>>>> Thus, move the PMCs enabling and disabling into the loop() asm blob and
>>>> ensure only the loop asm instructions would be counted, then the
>>>> instructions or branches events can be verified with an precise count
>>>> instead of an rough range.
>>>>
>>>> Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
>>>> ---
>>>>    x86/pmu.c | 83 +++++++++++++++++++++++++++++++++++++++++++++----------
>>>>    1 file changed, 69 insertions(+), 14 deletions(-)
>>>>
>>>> diff --git a/x86/pmu.c b/x86/pmu.c
>>>> index 46bed66c5c9f..88b89ad889b9 100644
>>>> --- a/x86/pmu.c
>>>> +++ b/x86/pmu.c
>>>> @@ -18,6 +18,20 @@
>>>>    #define EXPECTED_INSTR 17
>>>>    #define EXPECTED_BRNCH 5
>>>> +// Instrustion number of LOOP_ASM code
>>>> +#define LOOP_INSTRNS	10
>>>> +#define LOOP_ASM					\
>>>> +	"1: mov (%1), %2; add $64, %1;\n\t"		\
>>>> +	"nop; nop; nop; nop; nop; nop; nop;\n\t"	\
>>>> +	"loop 1b;\n\t"
>>>> +
>>>> +#define PRECISE_LOOP_ASM						\
>>>> +	"wrmsr;\n\t"							\
>>>> +	"mov %%ecx, %%edi; mov %%ebx, %%ecx;\n\t"			\
>>>> +	LOOP_ASM							\
>>>> +	"mov %%edi, %%ecx; xor %%eax, %%eax; xor %%edx, %%edx;\n\t"	\
>>>> +	"wrmsr;\n\t"
>>> Can we add "FEP" prefix into the above blob? This way, we can expand the
>>> testing for emulated instructions.
> Dapeng,
>
> Sorry, did not clarify that this is not a hard request. I am not
> pushing that this need to be done in your next version if it takes
> time to do so. (FEP is of couse nice to have :), but this test already
> supports it in somewhere else.).
>
> Once your next version is ready, please send it out as soon as you can
> and I am happy to give my reviews until it is merged.
>
> Thanks.
> -Mingwei

Yeah, I see there are some FEP related test cases in this test, I'm not 
sure if it can already meet the requirement, I would look at it later. 
Currently I'm busy on some high priority work, I suppose I have 
bandwidth to refresh a new version in next week. Thanks.


>>
>> Yeah, that sounds like a new feature request. I would add it in next
>> version.
>>
>>
>>>> +
>>>>    typedef struct {
>>>>    	uint32_t ctr;
>>>>    	uint64_t config;
>>>> @@ -54,13 +68,43 @@ char *buf;
>>>>    static struct pmu_event *gp_events;
>>>>    static unsigned int gp_events_size;
>>>> -static inline void loop(void)
>>>> +
>>>> +static inline void __loop(void)
>>>> +{
>>>> +	unsigned long tmp, tmp2, tmp3;
>>>> +
>>>> +	asm volatile(LOOP_ASM
>>>> +		     : "=c"(tmp), "=r"(tmp2), "=r"(tmp3)
>>>> +		     : "0"(N), "1"(buf));
>>>> +}
>>>> +
>>>> +/*
>>>> + * Enable and disable counters in a whole asm blob to ensure
>>>> + * no other instructions are counted in the time slot between
>>>> + * counters enabling and really LOOP_ASM code executing.
>>>> + * Thus counters can verify instructions and branches events
>>>> + * against precise counts instead of a rough valid count range.
>>>> + */
>>>> +static inline void __precise_count_loop(u64 cntrs)
>>>>    {
>>>>    	unsigned long tmp, tmp2, tmp3;
>>>> +	unsigned int global_ctl = pmu.msr_global_ctl;
>>>> +	u32 eax = cntrs & (BIT_ULL(32) - 1);
>>>> +	u32 edx = cntrs >> 32;
>>>> -	asm volatile("1: mov (%1), %2; add $64, %1; nop; nop; nop; nop; nop; nop; nop; loop 1b"
>>>> -			: "=c"(tmp), "=r"(tmp2), "=r"(tmp3): "0"(N), "1"(buf));
>>>> +	asm volatile(PRECISE_LOOP_ASM
>>>> +		     : "=b"(tmp), "=r"(tmp2), "=r"(tmp3)
>>>> +		     : "a"(eax), "d"(edx), "c"(global_ctl),
>>>> +		       "0"(N), "1"(buf)
>>>> +		     : "edi");
>>>> +}
>>>> +static inline void loop(u64 cntrs)
>>>> +{
>>>> +	if (!this_cpu_has_perf_global_ctrl())
>>>> +		__loop();
>>>> +	else
>>>> +		__precise_count_loop(cntrs);
>>>>    }
>>>>    volatile uint64_t irq_received;
>>>> @@ -159,18 +203,17 @@ static void __start_event(pmu_counter_t *evt, uint64_t count)
>>>>    	    ctrl = (ctrl & ~(0xf << shift)) | (usrospmi << shift);
>>>>    	    wrmsr(MSR_CORE_PERF_FIXED_CTR_CTRL, ctrl);
>>>>        }
>>>> -    global_enable(evt);
>>>>        apic_write(APIC_LVTPC, PMI_VECTOR);
>>>>    }
>>>>    static void start_event(pmu_counter_t *evt)
>>>>    {
>>>>    	__start_event(evt, 0);
>>>> +	global_enable(evt);
>>>>    }
>>>> -static void stop_event(pmu_counter_t *evt)
>>>> +static void __stop_event(pmu_counter_t *evt)
>>>>    {
>>>> -	global_disable(evt);
>>>>    	if (is_gp(evt)) {
>>>>    		wrmsr(MSR_GP_EVENT_SELECTx(event_to_global_idx(evt)),
>>>>    		      evt->config & ~EVNTSEL_EN);
>>>> @@ -182,14 +225,24 @@ static void stop_event(pmu_counter_t *evt)
>>>>    	evt->count = rdmsr(evt->ctr);
>>>>    }
>>>> +static void stop_event(pmu_counter_t *evt)
>>>> +{
>>>> +	global_disable(evt);
>>>> +	__stop_event(evt);
>>>> +}
>>>> +
>>>>    static noinline void measure_many(pmu_counter_t *evt, int count)
>>>>    {
>>>>    	int i;
>>>> +	u64 cntrs = 0;
>>>> +
>>>> +	for (i = 0; i < count; i++) {
>>>> +		__start_event(&evt[i], 0);
>>>> +		cntrs |= BIT_ULL(event_to_global_idx(&evt[i]));
>>>> +	}
>>>> +	loop(cntrs);
>>>>    	for (i = 0; i < count; i++)
>>>> -		start_event(&evt[i]);
>>>> -	loop();
>>>> -	for (i = 0; i < count; i++)
>>>> -		stop_event(&evt[i]);
>>>> +		__stop_event(&evt[i]);
>>>>    }
>>>>    static void measure_one(pmu_counter_t *evt)
>>>> @@ -199,9 +252,11 @@ static void measure_one(pmu_counter_t *evt)
>>>>    static noinline void __measure(pmu_counter_t *evt, uint64_t count)
>>>>    {
>>>> +	u64 cntrs = BIT_ULL(event_to_global_idx(evt));
>>>> +
>>>>    	__start_event(evt, count);
>>>> -	loop();
>>>> -	stop_event(evt);
>>>> +	loop(cntrs);
>>>> +	__stop_event(evt);
>>>>    }
>>>>    static bool verify_event(uint64_t count, struct pmu_event *e)
>>>> @@ -451,7 +506,7 @@ static void check_running_counter_wrmsr(void)
>>>>    	report_prefix_push("running counter wrmsr");
>>>>    	start_event(&evt);
>>>> -	loop();
>>>> +	__loop();
>>>>    	wrmsr(MSR_GP_COUNTERx(0), 0);
>>>>    	stop_event(&evt);
>>>>    	report(evt.count < gp_events[0].min, "cntr");
>>>> @@ -468,7 +523,7 @@ static void check_running_counter_wrmsr(void)
>>>>    	wrmsr(MSR_GP_COUNTERx(0), count);
>>>> -	loop();
>>>> +	__loop();
>>>>    	stop_event(&evt);
>>>>    	if (this_cpu_has_perf_global_status()) {
>>>> -- 
>>>> 2.34.1
>>>>