Re: [PATCH v8 08/24] drivers/perf: riscv: Fix counter mask iteration for RV32

[Samuel Holland]

Hi Atish,

On 2024-04-20 10:17 AM, Atish Patra wrote:
> For RV32, used_hw_ctrs can have more than 1 word if the firmware chooses
> to interleave firmware/hardware counters indicies. Even though it's a
> unlikely scenario, handle that case by iterating over all the words
> instead of just using the first word.
> 
> Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
> Signed-off-by: Atish Patra <atishp@xxxxxxxxxxxx>
> ---
>  drivers/perf/riscv_pmu_sbi.c | 21 ++++++++++++---------
>  1 file changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
> index f23501898657..4eacd89141a9 100644
> --- a/drivers/perf/riscv_pmu_sbi.c
> +++ b/drivers/perf/riscv_pmu_sbi.c
> @@ -652,10 +652,12 @@ static inline void pmu_sbi_stop_all(struct riscv_pmu *pmu)
>  static inline void pmu_sbi_stop_hw_ctrs(struct riscv_pmu *pmu)
>  {
>  	struct cpu_hw_events *cpu_hw_evt = this_cpu_ptr(pmu->hw_events);
> +	int i;
>  
> -	/* No need to check the error here as we can't do anything about the error */
> -	sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_STOP, 0,
> -		  cpu_hw_evt->used_hw_ctrs[0], 0, 0, 0, 0);
> +	for (i = 0; i < BITS_TO_LONGS(RISCV_MAX_COUNTERS); i++)
> +		/* No need to check the error here as we can't do anything about the error */
> +		sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_STOP, i * BITS_PER_LONG,
> +			  cpu_hw_evt->used_hw_ctrs[i], 0, 0, 0, 0);
>  }
>  
>  /*
> @@ -667,7 +669,7 @@ static inline void pmu_sbi_stop_hw_ctrs(struct riscv_pmu *pmu)
>  static inline void pmu_sbi_start_overflow_mask(struct riscv_pmu *pmu,
>  					       unsigned long ctr_ovf_mask)
>  {
> -	int idx = 0;
> +	int idx = 0, i;
>  	struct cpu_hw_events *cpu_hw_evt = this_cpu_ptr(pmu->hw_events);
>  	struct perf_event *event;
>  	unsigned long flag = SBI_PMU_START_FLAG_SET_INIT_VALUE;
> @@ -676,11 +678,12 @@ static inline void pmu_sbi_start_overflow_mask(struct riscv_pmu *pmu,
>  	struct hw_perf_event *hwc;
>  	u64 init_val = 0;
>  
> -	ctr_start_mask = cpu_hw_evt->used_hw_ctrs[0] & ~ctr_ovf_mask;
> -
> -	/* Start all the counters that did not overflow in a single shot */
> -	sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_START, 0, ctr_start_mask,
> -		  0, 0, 0, 0);
> +	for (i = 0; i < BITS_TO_LONGS(RISCV_MAX_COUNTERS); i++) {
> +		ctr_start_mask = cpu_hw_evt->used_hw_ctrs[i] & ~ctr_ovf_mask;

This is applying the mask for the first 32 logical counters to the both sets of
32 logical counters. ctr_ovf_mask needs to be 64 bits wide here, so each loop
iteration can apply the correct half of the mask.

Regards,
Samuel

> +		/* Start all the counters that did not overflow in a single shot */
> +		sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_START, i * BITS_PER_LONG, ctr_start_mask,
> +			0, 0, 0, 0);
> +	}
>  
>  	/* Reinitialize and start all the counter that overflowed */
>  	while (ctr_ovf_mask) {