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

[Ricardo Koller <ricarkol@google.com>]

On Tue, Dec 13, 2022 at 12:36:14PM +0000, Alexandru Elisei wrote:
> 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.
> 

Ah, right. Yeah, that message is confusing. It should be the short
version of "Inrementing at 32-bits resulted in the right value".

> 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.

The last commit adds tests using ALL_SET64.  Tests can be run in two
modes: overflow_at_64bits and not.  However, this test,
test_chained_counters(), and all other chained tests only use the
!overflow_at_64bits mode (even after the last commit). The reason is
that there are no CHAIN events when overflowing at 64-bits (more details
in the commit message). But, don't worry, there are lots of tests that
check wrapping at 64-bits (overflow_at_64bits=true).

> 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.

Ah, yes, code is correct but that's indeed confusing.

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

Ack. Will update for v2.

Thanks!
Ricardo

> 
> 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
> >