[kvm-unit-tests,PATCHv6,2/3] arm: pmu: Check cycle count increases

Ensure that reads of the PMCCNTR_EL0 are monotonically increasing,
even for the smallest delta of two subsequent reads.

Signed-off-by: Christopher Covington <cov@codeaurora.org>
Reviewed-by: Andrew Jones <drjones@redhat.com>
---
 arm/pmu.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

On 10/11/2016 01:40 PM, Christopher Covington wrote:
> Ensure that reads of the PMCCNTR_EL0 are monotonically increasing,
> even for the smallest delta of two subsequent reads.
> 
> Signed-off-by: Christopher Covington <cov@codeaurora.org>
> Reviewed-by: Andrew Jones <drjones@redhat.com>
> ---
>  arm/pmu.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 60 insertions(+)
> 
> diff --git a/arm/pmu.c b/arm/pmu.c
> index 42d0ee1..4334de4 100644
> --- a/arm/pmu.c
> +++ b/arm/pmu.c
> @@ -14,6 +14,8 @@
>   */
>  #include "libcflat.h"
>  
> +#define NR_SAMPLES 10
> +
>  #if defined(__arm__)
>  static inline uint32_t get_pmcr(void)
>  {
> @@ -22,6 +24,25 @@ static inline uint32_t get_pmcr(void)
>  	asm volatile("mrc p15, 0, %0, c9, c12, 0" : "=r" (ret));
>  	return ret;
>  }
> +
> +static inline void set_pmcr(uint32_t pmcr)
> +{
> +	asm volatile("mcr p15, 0, %0, c9, c12, 0" : : "r" (pmcr));
> +}
> +
> +/*
> + * While PMCCNTR can be accessed as a 64 bit coprocessor register, returning 64
> + * bits doesn't seem worth the trouble when differential usage of the result is
> + * expected (with differences that can easily fit in 32 bits). So just return
> + * the lower 32 bits of the cycle count in AArch32.
> + */
> +static inline unsigned long get_pmccntr(void)
> +{
> +	unsigned long cycles;
> +
> +	asm volatile("mrc p15, 0, %0, c9, c13, 0" : "=r" (cycles));
> +	return cycles;
> +}
>  #elif defined(__aarch64__)
>  static inline uint32_t get_pmcr(void)
>  {
> @@ -30,6 +51,19 @@ static inline uint32_t get_pmcr(void)
>  	asm volatile("mrs %0, pmcr_el0" : "=r" (ret));
>  	return ret;
>  }
> +
> +static inline void set_pmcr(uint32_t pmcr)
> +{
> +	asm volatile("msr pmcr_el0, %0" : : "r" (pmcr));
> +}
> +
> +static inline unsigned long get_pmccntr(void)
> +{
> +	unsigned long cycles;
> +
> +	asm volatile("mrs %0, pmccntr_el0" : "=r" (cycles));
> +	return cycles;
> +}
>  #endif
>  
>  struct pmu_data {
> @@ -72,11 +106,37 @@ static bool check_pmcr(void)
>  	return pmu.implementer != 0;
>  }
>  
> +/*
> + * Ensure that the cycle counter progresses between back-to-back reads.
> + */
> +static bool check_cycles_increase(void)
> +{
> +	struct pmu_data pmu = {0};

Compilation error on my machine:

arm/pmu.c: In function ‘check_cycles_increase’:
arm/pmu.c:148:9: error: missing braces around initializer
[-Werror=missing-braces]
  struct pmu_data pmu = {0};

Same for Patch 3.


> +
> +	pmu.enable = 1;
> +	set_pmcr(pmu.pmcr_el0);
> +
> +	for (int i = 0; i < NR_SAMPLES; i++) {
> +		unsigned long a, b;
> +
> +		a = get_pmccntr();
> +		b = get_pmccntr();
> +
> +		if (a >= b) {
> +			printf("Read %ld then %ld.\n", a, b);
> +			return false;
> +		}
> +	}
> +
> +	return true;
> +}
> +
>  int main(void)
>  {
>  	report_prefix_push("pmu");
>  
>  	report("Control register", check_pmcr());
> +	report("Monotonically increasing cycle count", check_cycles_increase());
>  
>  	return report_summary();
>  }
>

Hi Wei,

On 10/12/2016 11:49 AM, Wei Huang wrote:
> On 10/11/2016 01:40 PM, Christopher Covington wrote:
>> Ensure that reads of the PMCCNTR_EL0 are monotonically increasing,
>> even for the smallest delta of two subsequent reads.
>>
>> Signed-off-by: Christopher Covington <cov@codeaurora.org>
>> Reviewed-by: Andrew Jones <drjones@redhat.com>
>> ---
>>  arm/pmu.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 60 insertions(+)
>>
>> diff --git a/arm/pmu.c b/arm/pmu.c
>> index 42d0ee1..4334de4 100644
>> --- a/arm/pmu.c
>> +++ b/arm/pmu.c
>> @@ -14,6 +14,8 @@
>>   */
>>  #include "libcflat.h"
>>  
>> +#define NR_SAMPLES 10
>> +
>>  #if defined(__arm__)
>>  static inline uint32_t get_pmcr(void)
>>  {
>> @@ -22,6 +24,25 @@ static inline uint32_t get_pmcr(void)
>>  	asm volatile("mrc p15, 0, %0, c9, c12, 0" : "=r" (ret));
>>  	return ret;
>>  }
>> +
>> +static inline void set_pmcr(uint32_t pmcr)
>> +{
>> +	asm volatile("mcr p15, 0, %0, c9, c12, 0" : : "r" (pmcr));
>> +}
>> +
>> +/*
>> + * While PMCCNTR can be accessed as a 64 bit coprocessor register, returning 64
>> + * bits doesn't seem worth the trouble when differential usage of the result is
>> + * expected (with differences that can easily fit in 32 bits). So just return
>> + * the lower 32 bits of the cycle count in AArch32.
>> + */
>> +static inline unsigned long get_pmccntr(void)
>> +{
>> +	unsigned long cycles;
>> +
>> +	asm volatile("mrc p15, 0, %0, c9, c13, 0" : "=r" (cycles));
>> +	return cycles;
>> +}
>>  #elif defined(__aarch64__)
>>  static inline uint32_t get_pmcr(void)
>>  {
>> @@ -30,6 +51,19 @@ static inline uint32_t get_pmcr(void)
>>  	asm volatile("mrs %0, pmcr_el0" : "=r" (ret));
>>  	return ret;
>>  }
>> +
>> +static inline void set_pmcr(uint32_t pmcr)
>> +{
>> +	asm volatile("msr pmcr_el0, %0" : : "r" (pmcr));
>> +}
>> +
>> +static inline unsigned long get_pmccntr(void)
>> +{
>> +	unsigned long cycles;
>> +
>> +	asm volatile("mrs %0, pmccntr_el0" : "=r" (cycles));
>> +	return cycles;
>> +}
>>  #endif
>>  
>>  struct pmu_data {
>> @@ -72,11 +106,37 @@ static bool check_pmcr(void)
>>  	return pmu.implementer != 0;
>>  }
>>  
>> +/*
>> + * Ensure that the cycle counter progresses between back-to-back reads.
>> + */
>> +static bool check_cycles_increase(void)
>> +{
>> +	struct pmu_data pmu = {0};
> 
> Compilation error on my machine:
> 
> arm/pmu.c: In function ‘check_cycles_increase’:
> arm/pmu.c:148:9: error: missing braces around initializer
> [-Werror=missing-braces]
>   struct pmu_data pmu = {0};
> 
> Same for Patch 3.

"...So your compiler complains about {0}? Is there a problem besides the
warning? If not, then I'm still a bit inclined to keep the code neat. The
warnings will go away with compiler updates."

https://lists.gnu.org/archive/html/qemu-devel/2015-10/msg06064.html

Thanks,
Cov

On 10/12/2016 01:10 PM, Christopher Covington wrote:
> Hi Wei,
> 
> On 10/12/2016 11:49 AM, Wei Huang wrote:
>> On 10/11/2016 01:40 PM, Christopher Covington wrote:
>>> Ensure that reads of the PMCCNTR_EL0 are monotonically increasing,
>>> even for the smallest delta of two subsequent reads.
>>>
>>> Signed-off-by: Christopher Covington <cov@codeaurora.org>
>>> Reviewed-by: Andrew Jones <drjones@redhat.com>
>>> ---
>>>  arm/pmu.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>>  1 file changed, 60 insertions(+)
>>>
>>> diff --git a/arm/pmu.c b/arm/pmu.c
>>> index 42d0ee1..4334de4 100644
>>> --- a/arm/pmu.c
>>> +++ b/arm/pmu.c
>>> @@ -14,6 +14,8 @@
>>>   */
>>>  #include "libcflat.h"
>>>  
>>> +#define NR_SAMPLES 10
>>> +
>>>  #if defined(__arm__)
>>>  static inline uint32_t get_pmcr(void)
>>>  {
>>> @@ -22,6 +24,25 @@ static inline uint32_t get_pmcr(void)
>>>  	asm volatile("mrc p15, 0, %0, c9, c12, 0" : "=r" (ret));
>>>  	return ret;
>>>  }
>>> +
>>> +static inline void set_pmcr(uint32_t pmcr)
>>> +{
>>> +	asm volatile("mcr p15, 0, %0, c9, c12, 0" : : "r" (pmcr));
>>> +}
>>> +
>>> +/*
>>> + * While PMCCNTR can be accessed as a 64 bit coprocessor register, returning 64
>>> + * bits doesn't seem worth the trouble when differential usage of the result is
>>> + * expected (with differences that can easily fit in 32 bits). So just return
>>> + * the lower 32 bits of the cycle count in AArch32.
>>> + */
>>> +static inline unsigned long get_pmccntr(void)
>>> +{
>>> +	unsigned long cycles;
>>> +
>>> +	asm volatile("mrc p15, 0, %0, c9, c13, 0" : "=r" (cycles));
>>> +	return cycles;
>>> +}
>>>  #elif defined(__aarch64__)
>>>  static inline uint32_t get_pmcr(void)
>>>  {
>>> @@ -30,6 +51,19 @@ static inline uint32_t get_pmcr(void)
>>>  	asm volatile("mrs %0, pmcr_el0" : "=r" (ret));
>>>  	return ret;
>>>  }
>>> +
>>> +static inline void set_pmcr(uint32_t pmcr)
>>> +{
>>> +	asm volatile("msr pmcr_el0, %0" : : "r" (pmcr));
>>> +}
>>> +
>>> +static inline unsigned long get_pmccntr(void)
>>> +{
>>> +	unsigned long cycles;
>>> +
>>> +	asm volatile("mrs %0, pmccntr_el0" : "=r" (cycles));
>>> +	return cycles;
>>> +}
>>>  #endif
>>>  
>>>  struct pmu_data {
>>> @@ -72,11 +106,37 @@ static bool check_pmcr(void)
>>>  	return pmu.implementer != 0;
>>>  }
>>>  
>>> +/*
>>> + * Ensure that the cycle counter progresses between back-to-back reads.
>>> + */
>>> +static bool check_cycles_increase(void)
>>> +{
>>> +	struct pmu_data pmu = {0};
>>
>> Compilation error on my machine:
>>
>> arm/pmu.c: In function ‘check_cycles_increase’:
>> arm/pmu.c:148:9: error: missing braces around initializer
>> [-Werror=missing-braces]
>>   struct pmu_data pmu = {0};
>>
>> Same for Patch 3.
> 
> "...So your compiler complains about {0}? Is there a problem besides the
> warning? If not, then I'm still a bit inclined to keep the code neat. The
> warnings will go away with compiler updates."

Indeed my stock GCC compiler is a bit old - 4.8.5; newer version can fix
it. But note this a compilation error which prevents the binary from
being built and will last a while. Could we use double-braces, pmu =
{{0}}, as a solution?

-Wei

> 
> https://lists.gnu.org/archive/html/qemu-devel/2015-10/msg06064.html
> 
> Thanks,
> Cov
>