Re: [kvm-unit-tests PATCH 04/10] arm: pmu: Check Required Event Support

[Andre Przywara <andre.przywara@arm.com>]

On Mon, 16 Dec 2019 21:47:51 +0100
Eric Auger <eric.auger@redhat.com> wrote:

Hi Eric,

> If event counters are implemented check the common events
> required by the PMUv3 are implemented.
> 
> Some are unconditionally required (SW_INCR, CPU_CYCLES,
> either INST_RETIRED or INST_SPEC). Some others only are
> required if the implementation implements some other features.
> 
> Check those wich are unconditionally required.
> 
> This test currently fails on TCG as neither INST_RETIRED
> or INST_SPEC are supported.
> 
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> 
> ---
> 
> v1 ->v2:
> - add a comment to explain the PMCEID0/1 splits
> ---
>  arm/pmu.c         | 71 +++++++++++++++++++++++++++++++++++++++++++++++
>  arm/unittests.cfg |  6 ++++
>  2 files changed, 77 insertions(+)
> 
> diff --git a/arm/pmu.c b/arm/pmu.c
> index d24857e..d88ef22 100644
> --- a/arm/pmu.c
> +++ b/arm/pmu.c
> @@ -101,6 +101,10 @@ static inline void precise_instrs_loop(int loop, uint32_t pmcr)
>  	: [pmcr] "r" (pmcr), [z] "r" (0)
>  	: "cc");
>  }
> +
> +/* event counter tests only implemented for aarch64 */
> +static void test_event_introspection(void) {}
> +
>  #elif defined(__aarch64__)
>  #define ID_AA64DFR0_PERFMON_SHIFT 8
>  #define ID_AA64DFR0_PERFMON_MASK  0xf
> @@ -139,6 +143,70 @@ static inline void precise_instrs_loop(int loop, uint32_t pmcr)
>  	: [pmcr] "r" (pmcr)
>  	: "cc");
>  }
> +
> +#define PMCEID1_EL0 sys_reg(11, 3, 9, 12, 7)
> +
> +static bool is_event_supported(uint32_t n, bool warn)
> +{
> +	uint64_t pmceid0 = read_sysreg(pmceid0_el0);
> +	uint64_t pmceid1 = read_sysreg_s(PMCEID1_EL0);
> +	bool supported;
> +	uint32_t reg;
> +
> +	/*
> +	 * The low 32-bits of PMCEID0/1 respectly describe
> +	 * event support for events 0-31/32-63. Their High
> +	 * 32-bits describe support for extended events
> +	 * starting at 0x4000, using the same split.
> +	 */
> +	if (n >= 0x0  && n <= 0x1F)
> +		reg = pmceid0 & 0xFFFFFFFF;
> +	else if  (n >= 0x4000 && n <= 0x401F)
> +		reg = pmceid0 >> 32;
> +	else if (n >= 0x20  && n <= 0x3F)
> +		reg = pmceid1 & 0xFFFFFFFF;
> +	else if (n >= 0x4020 && n <= 0x403F)
> +		reg = pmceid1 >> 32;
> +	else
> +		abort();
> +
> +	supported =  reg & (1 << n);

Don't we need to mask off everything but the lowest 5 bits of "n"? Probably also using "1U" is better.

> +	if (!supported && warn)
> +		report_info("event %d is not supported", n);
> +	return supported;
> +}
> +
> +static void test_event_introspection(void)

"introspection" sounds quite sophisticated. Are you planning to extend this? If not, could we maybe rename it to "test_available_events"?

> +{
> +	bool required_events;
> +
> +	if (!pmu.nb_implemented_counters) {
> +		report_skip("No event counter, skip ...");
> +		return;
> +	}
> +
> +	/* PMUv3 requires an implementation includes some common events */
> +	required_events = is_event_supported(0x0, true) /* SW_INCR */ &&
> +			  is_event_supported(0x11, true) /* CPU_CYCLES */ &&
> +			  (is_event_supported(0x8, true) /* INST_RETIRED */ ||
> +			   is_event_supported(0x1B, true) /* INST_PREC */);
> +
> +	if (pmu.version == 0x4) {
> +		/* ARMv8.1 PMU: STALL_FRONTEND and STALL_BACKEND are required */
> +		required_events = required_events ||
> +				  is_event_supported(0x23, true) ||

Shouldn't those two operators be '&&' instead?

> +				  is_event_supported(0x24, true);
> +	}
> +
> +	/*
> +	 * L1D_CACHE_REFILL(0x3) and L1D_CACHE(0x4) are only required if
> +	 * L1 data / unified cache. BR_MIS_PRED(0x10), BR_PRED(0x12) are only
> +	 * required if program-flow prediction is implemented.
> +	 */

Is this a TODO?

Cheers,
Andre


> +
> +	report(required_events, "Check required events are implemented");
> +}
> +
>  #endif
>  
>  /*
> @@ -326,6 +394,9 @@ int main(int argc, char *argv[])
>  		       "Monotonically increasing cycle count");
>  		report(check_cpi(cpi), "Cycle/instruction ratio");
>  		pmccntr64_test();
> +	} else if (strcmp(argv[1], "event-introspection") == 0) {
> +		report_prefix_push(argv[1]);
> +		test_event_introspection();
>  	} else {
>  		report_abort("Unknown sub-test '%s'", argv[1]);
>  	}
> diff --git a/arm/unittests.cfg b/arm/unittests.cfg
> index 79f0d7a..4433ef3 100644
> --- a/arm/unittests.cfg
> +++ b/arm/unittests.cfg
> @@ -66,6 +66,12 @@ file = pmu.flat
>  groups = pmu
>  extra_params = -append 'cycle-counter 0'
>  
> +[pmu-event-introspection]
> +file = pmu.flat
> +groups = pmu
> +arch = arm64
> +extra_params = -append 'event-introspection'
> +
>  # Test PMU support (TCG) with -icount IPC=1
>  #[pmu-tcg-icount-1]
>  #file = pmu.flat