Re: [PATCH kvm-unit-tests] pmu: fixes for Sandy Bridge hosts

[Gleb Natapov <gleb@redhat.com>]

On Thu, May 30, 2013 at 07:43:07PM +0200, Paolo Bonzini wrote:
> This patch includes two fixes for SB:
> 
> * the 3rd fixed counter ("ref cpu cycles") can sometimes report
>   less than the number of iterations
> 
Is it documented? It is strange for "architectural" counter to behave
differently on different architectures.

> * there is an 8th counter which causes out of bounds accesses
>   to gp_event or check_counters_many's cnt array
> 
> There is still a bug in KVM, because the "pmu all counters-0"
> test fails.  (It passes if you use any 6 of the 8 gp counters,
> fails if you use 7 or 8).
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  x86/pmu.c | 21 +++++++++++++++------
>  1 file changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/x86/pmu.c b/x86/pmu.c
> index 2c46f31..dca753a 100644
> --- a/x86/pmu.c
> +++ b/x86/pmu.c
> @@ -88,9 +88,10 @@ struct pmu_event {
>  }, fixed_events[] = {
>  	{"fixed 1", MSR_CORE_PERF_FIXED_CTR0, 10*N, 10.2*N},
>  	{"fixed 2", MSR_CORE_PERF_FIXED_CTR0 + 1, 1*N, 30*N},
> -	{"fixed 3", MSR_CORE_PERF_FIXED_CTR0 + 2, 1*N, 30*N}
> +	{"fixed 3", MSR_CORE_PERF_FIXED_CTR0 + 2, 0.1*N, 30*N}
>  };
>  
> +static int num_counters;
>  static int tests, failures;
>  
>  char *buf;
> @@ -237,7 +238,7 @@ static void check_gp_counter(struct pmu_event *evt)
>  	};
>  	int i;
>  
> -	for (i = 0; i < eax.split.num_counters; i++, cnt.ctr++) {
> +	for (i = 0; i < num_counters; i++, cnt.ctr++) {
>  		cnt.count = 0;
>  		measure(&cnt, 1);
>  		report(evt->name, i, verify_event(cnt.count, evt));
> @@ -276,7 +277,7 @@ static void check_counters_many(void)
>  	pmu_counter_t cnt[10];
>  	int i, n;
>  
> -	for (i = 0, n = 0; n < eax.split.num_counters; i++) {
> +	for (i = 0, n = 0; n < num_counters; i++) {
>  		if (ebx.full & (1 << i))
>  			continue;
>  
> @@ -316,10 +317,10 @@ static void check_counter_overflow(void)
>  	/* clear status before test */
>  	wrmsr(MSR_CORE_PERF_GLOBAL_OVF_CTRL, rdmsr(MSR_CORE_PERF_GLOBAL_STATUS));
>  
> -	for (i = 0; i < eax.split.num_counters + 1; i++, cnt.ctr++) {
> +	for (i = 0; i < num_counters + 1; i++, cnt.ctr++) {
>  		uint64_t status;
>  		int idx;
> -		if (i == eax.split.num_counters)
> +		if (i == num_counters)
>  			cnt.ctr = fixed_events[0].unit_sel;
>  		if (i % 2)
>  			cnt.config |= EVNTSEL_INT;
> @@ -355,7 +356,7 @@ static void check_rdpmc(void)
>  	uint64_t val = 0x1f3456789ull;
>  	int i;
>  
> -	for (i = 0; i < eax.split.num_counters; i++) {
> +	for (i = 0; i < num_counters; i++) {
>  		uint64_t x = (val & 0xffffffff) |
>  			((1ull << (eax.split.bit_width - 32)) - 1) << 32;
>  		wrmsr(MSR_IA32_PERFCTR0 + i, val);
> @@ -395,6 +396,14 @@ int main(int ac, char **av)
>  	printf("Fixed counters:      %d\n", edx.split.num_counters_fixed);
>  	printf("Fixed counter width: %d\n", edx.split.bit_width_fixed);
>  
> +	num_counters = eax.split.num_counters;
> +	if (num_counters > ARRAY_SIZE(gp_events))
> +		num_counters = ARRAY_SIZE(gp_events);
> +
>  	apic_write(APIC_LVTPC, PC_VECTOR);
>  
>  	check_gp_counters();
> -- 
> 1.8.2.1
> 
> --
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--
			Gleb.