Re: [Qemu-devel] [kvm-unit-tests PATCHv5 2/3] arm: pmu: Check cycle count increases

[Christopher Covington <cov@codeaurora.org>]

On 10/26/2015 11:58 AM, Andrew Jones wrote:
> On Mon, Oct 26, 2015 at 11:38:49AM -0400, 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>
>> ---
>>  arm/pmu.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 60 insertions(+)
>>
>> diff --git a/arm/pmu.c b/arm/pmu.c
>> index 42d0ee1..c44d708 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} };
> 
> One set of {} is enough, and looks better.

As I tried to mention in the cover letter, that can trigger a spurious GCC
warning (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53119). But if you don't
mind, I don't mind.

> Otherwise
> Reviewed-by: Andrew Jones <drjones@redhat.com>

Thanks!

Christopher Covington

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