On Tue, Nov 08, 2016 at 12:17:14PM -0600, Wei Huang wrote:
> From: Christopher Covington <cov@xxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxx>
> Signed-off-by: Wei Huang <wei@xxxxxxxxxx>
> ---
> arm/pmu.c | 98 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 98 insertions(+)
>
> diff --git a/arm/pmu.c b/arm/pmu.c
> index 0b29088..d5e3ac3 100644
> --- a/arm/pmu.c
> +++ b/arm/pmu.c
> @@ -14,6 +14,7 @@
> */
> #include "libcflat.h"
>
> +#define PMU_PMCR_E (1 << 0)
> #define PMU_PMCR_N_SHIFT 11
> #define PMU_PMCR_N_MASK 0x1f
> #define PMU_PMCR_ID_SHIFT 16
> @@ -21,6 +22,10 @@
> #define PMU_PMCR_IMP_SHIFT 24
> #define PMU_PMCR_IMP_MASK 0xff
>
> +#define PMU_CYCLE_IDX 31
> +
> +#define NR_SAMPLES 10
> +
> #if defined(__arm__)
> static inline uint32_t pmcr_read(void)
> {
> @@ -29,6 +34,47 @@ static inline uint32_t pmcr_read(void)
> asm volatile("mrc p15, 0, %0, c9, c12, 0" : "=r" (ret));
> return ret;
> }
> +
> +static inline void pmcr_write(uint32_t value)
> +{
> + asm volatile("mcr p15, 0, %0, c9, c12, 0" : : "r" (value));
> +}
> +
> +static inline void pmselr_write(uint32_t value)
> +{
> + asm volatile("mcr p15, 0, %0, c9, c12, 5" : : "r" (value));
> +}
> +
> +static inline void pmxevtyper_write(uint32_t value)
> +{
> + asm volatile("mcr p15, 0, %0, c9, c13, 1" : : "r" (value));
> +}
> +
> +/*
> + * 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.
Like I said in the last review, I'd rather we not do this. We should
return the full value and then the test case should confirm the upper
32 bits are zero.
> + */
> +static inline uint32_t pmccntr_read(void)
> +{
> + uint32_t cycles;
> +
> + asm volatile("mrc p15, 0, %0, c9, c13, 0" : "=r" (cycles));
> + return cycles;
> +}
> +
> +static inline void pmcntenset_write(uint32_t value)
> +{
> + asm volatile("mcr p15, 0, %0, c9, c12, 1" : : "r" (value));
> +}
> +
> +/* PMCCFILTR is an obsolete name for PMXEVTYPER31 in ARMv7 */
> +static inline void pmccfiltr_write(uint32_t value)
> +{
> + pmselr_write(PMU_CYCLE_IDX);
> + pmxevtyper_write(value);
> +}
> #elif defined(__aarch64__)
> static inline uint32_t pmcr_read(void)
> {
> @@ -37,6 +83,29 @@ static inline uint32_t pmcr_read(void)
> asm volatile("mrs %0, pmcr_el0" : "=r" (ret));
> return ret;
> }
> +
> +static inline void pmcr_write(uint32_t value)
> +{
> + asm volatile("msr pmcr_el0, %0" : : "r" (value));
> +}
> +
> +static inline uint32_t pmccntr_read(void)
> +{
> + uint32_t cycles;
> +
> + asm volatile("mrs %0, pmccntr_el0" : "=r" (cycles));
> + return cycles;
> +}
> +
> +static inline void pmcntenset_write(uint32_t value)
> +{
> + asm volatile("msr pmcntenset_el0, %0" : : "r" (value));
> +}
> +
> +static inline void pmccfiltr_write(uint32_t value)
> +{
> + asm volatile("msr pmccfiltr_el0, %0" : : "r" (value));
> +}
> #endif
>
> /*
> @@ -63,11 +132,40 @@ static bool check_pmcr(void)
> return ((pmcr >> PMU_PMCR_IMP_SHIFT) & PMU_PMCR_IMP_MASK) != 0;
> }
>
> +/*
> + * Ensure that the cycle counter progresses between back-to-back reads.
> + */
> +static bool check_cycles_increase(void)
> +{
> + pmcr_write(pmcr_read() | PMU_PMCR_E);
> +
> + for (int i = 0; i < NR_SAMPLES; i++) {
> + unsigned long a, b;
> +
> + a = pmccntr_read();
> + b = pmccntr_read();
> +
> + if (a >= b) {
> + printf("Read %ld then %ld.\n", a, b);
> + return false;
> + }
> + }
> +
> + pmcr_write(pmcr_read() & ~PMU_PMCR_E);
> +
> + return true;
> +}
> +
> int main(void)
> {
> report_prefix_push("pmu");
>
> + /* init for PMU event access, right now only care about cycle count */
> + pmcntenset_write(1 << PMU_CYCLE_IDX);
> + pmccfiltr_write(0); /* count cycles in EL0, EL1, but not EL2 */
> +
> report("Control register", check_pmcr());
> + report("Monotonically increasing cycle count", check_cycles_increase());
>
> return report_summary();
> }
> --
> 1.8.3.1
Besides needing to use u64's for registers that return u64's, it
looks good to me.
drew
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