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

[Mingwei Zhang]

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@xxxxxxxxxxxxxxx>
> > > ---
> > >   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, 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
> > >