Re: [kvm-unit-tests PATCH 1/3] arm: pmu: Fix overflow checks for PMUv3p5 long counters

[Alexandru Elisei <alexandru.elisei@arm.com>]

Hi,

Some more comments below.

On Fri, Dec 02, 2022 at 04:55:25AM +0000, Ricardo Koller wrote:
> PMUv3p5 uses 64-bit counters irrespective of whether the PMU is configured
> for overflowing at 32 or 64-bits. The consequence is that tests that check
> the counter values after overflowing should not assume that values will be
> wrapped around 32-bits: they overflow into the other half of the 64-bit
> counters on PMUv3p5.
> 
> Fix tests by correctly checking overflowing-counters against the expected
> 64-bit value.
> 
> Signed-off-by: Ricardo Koller <ricarkol@google.com>
> ---
>  arm/pmu.c | 29 ++++++++++++++++++-----------
>  1 file changed, 18 insertions(+), 11 deletions(-)
> 
> diff --git a/arm/pmu.c b/arm/pmu.c
> index cd47b14..eeac984 100644
> --- a/arm/pmu.c
> +++ b/arm/pmu.c
> @@ -54,10 +54,10 @@
>  #define EXT_COMMON_EVENTS_LOW	0x4000
>  #define EXT_COMMON_EVENTS_HIGH	0x403F
>  
> -#define ALL_SET			0xFFFFFFFF
> -#define ALL_CLEAR		0x0
> -#define PRE_OVERFLOW		0xFFFFFFF0
> -#define PRE_OVERFLOW2		0xFFFFFFDC
> +#define ALL_SET			0x00000000FFFFFFFFULL
> +#define ALL_CLEAR		0x0000000000000000ULL
> +#define PRE_OVERFLOW		0x00000000FFFFFFF0ULL
> +#define PRE_OVERFLOW2		0x00000000FFFFFFDCULL
>  
>  #define PMU_PPI			23
>  
> @@ -538,6 +538,7 @@ static void test_mem_access(void)
>  static void test_sw_incr(void)
>  {
>  	uint32_t events[] = {SW_INCR, SW_INCR};
> +	uint64_t cntr0;
>  	int i;
>  
>  	if (!satisfy_prerequisites(events, ARRAY_SIZE(events)))
> @@ -572,9 +573,9 @@ static void test_sw_incr(void)
>  		write_sysreg(0x3, pmswinc_el0);
>  
>  	isb();
> -	report(read_regn_el0(pmevcntr, 0)  == 84, "counter #1 after + 100 SW_INCR");
> -	report(read_regn_el0(pmevcntr, 1)  == 100,
> -		"counter #0 after + 100 SW_INCR");
> +	cntr0 = (pmu.version < ID_DFR0_PMU_V3_8_5) ? 84 : PRE_OVERFLOW + 100;
> +	report(read_regn_el0(pmevcntr, 0) == cntr0, "counter #0 after + 100 SW_INCR");
> +	report(read_regn_el0(pmevcntr, 1) == 100, "counter #1 after + 100 SW_INCR");
>  	report_info("counter values after 100 SW_INCR #0=%ld #1=%ld",
>  		    read_regn_el0(pmevcntr, 0), read_regn_el0(pmevcntr, 1));
>  	report(read_sysreg(pmovsclr_el0) == 0x1,
> @@ -584,6 +585,7 @@ static void test_sw_incr(void)
>  static void test_chained_counters(void)
>  {
>  	uint32_t events[] = {CPU_CYCLES, CHAIN};
> +	uint64_t cntr1;
>  
>  	if (!satisfy_prerequisites(events, ARRAY_SIZE(events)))
>  		return;
> @@ -618,13 +620,16 @@ static void test_chained_counters(void)
>  
>  	precise_instrs_loop(22, pmu.pmcr_ro | PMU_PMCR_E);
>  	report_info("overflow reg = 0x%lx", read_sysreg(pmovsclr_el0));
> -	report(!read_regn_el0(pmevcntr, 1), "CHAIN counter #1 wrapped");
> +	cntr1 = (pmu.version < ID_DFR0_PMU_V3_8_5) ? 0 : ALL_SET + 1;
> +	report(read_regn_el0(pmevcntr, 1) == cntr1, "CHAIN counter #1 wrapped");

It looks to me like the intention of the test was to check that the counter
programmed with the CHAIN event wraps, judging from the report message.

I think it would be interesting to keep that by programming counter #1 with
~0ULL when PMUv3p5 (maybe call it ALL_SET64?) and test the counter value
against 0. Alternatively, the report message can be modified, and "wrapped"
replaced with "incremented" (or something like that), to avoid confusion.

> +
>  	report(read_sysreg(pmovsclr_el0) == 0x3, "overflow on even and odd counters");
>  }
>  
>  static void test_chained_sw_incr(void)
>  {
>  	uint32_t events[] = {SW_INCR, CHAIN};
> +	uint64_t cntr0, cntr1;
>  	int i;
>  
>  	if (!satisfy_prerequisites(events, ARRAY_SIZE(events)))
> @@ -665,10 +670,12 @@ static void test_chained_sw_incr(void)
>  		write_sysreg(0x1, pmswinc_el0);
>  
>  	isb();
> +	cntr0 = (pmu.version < ID_DFR0_PMU_V3_8_5) ? 0 : ALL_SET + 1;
> +	cntr1 = (pmu.version < ID_DFR0_PMU_V3_8_5) ? 84 : PRE_OVERFLOW + 100;
>  	report((read_sysreg(pmovsclr_el0) == 0x3) &&
> -		(read_regn_el0(pmevcntr, 1) == 0) &&
> -		(read_regn_el0(pmevcntr, 0) == 84),
> -		"expected overflows and values after 100 SW_INCR/CHAIN");
> +	       (read_regn_el0(pmevcntr, 1) == cntr0) &&
> +	       (read_regn_el0(pmevcntr, 0) == cntr1),

This is hard to parse, it would be better if counter 0 is compared against
cntr0 and counter 1 against cntr1.

Also, same suggestion here, looks like the test wants to check that the
odd-numbered counter wraps around when counting the CHAIN event.

Thanks,
Alex

> +	       "expected overflows and values after 100 SW_INCR/CHAIN");
>  	report_info("overflow=0x%lx, #0=%ld #1=%ld", read_sysreg(pmovsclr_el0),
>  		    read_regn_el0(pmevcntr, 0), read_regn_el0(pmevcntr, 1));
>  }
> -- 
> 2.39.0.rc0.267.gcb52ba06e7-goog
>