Re: [PATCH v2 06/10] drivers: perf: Implement perf event mmap support in the legacy backend

Andrew Jones
2023-05-31T14:28:08Z

On Fri, May 12, 2023 at 10:53:17AM +0200, Alexandre Ghiti wrote:
> Implement the needed callbacks in the legacy driver so that we can
> directly access the counters through perf in userspace.
>
> Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
> ---
> drivers/perf/riscv_pmu_legacy.c | 28 ++++++++++++++++++++++++++++
> 1 file changed, 28 insertions(+)
>
> diff --git a/drivers/perf/riscv_pmu_legacy.c b/drivers/perf/riscv_pmu_legacy.c
> index ffe09d857366..f0f5bd856f66 100644
> --- a/drivers/perf/riscv_pmu_legacy.c
> +++ b/drivers/perf/riscv_pmu_legacy.c
> @@ -74,6 +74,31 @@ static void pmu_legacy_ctr_start(struct perf_event *event, u64 ival)
> local64_set(&hwc->prev_count, initial_val);
> }
>
> +static uint8_t pmu_legacy_csr_index(struct perf_event *event)
> +{
> + return event->hw.idx;
> +}
> +
> +static void pmu_legacy_event_mapped(struct perf_event *event, struct mm_struct *mm)
> +{
> + /* In legacy mode, the first 3 CSRs are available. */

Shouldn't this be

/* In legacy mode, the first and third CSR are available. */

?

> + if (event->attr.config != PERF_COUNT_HW_CPU_CYCLES &&
> + event->attr.config != PERF_COUNT_HW_INSTRUCTIONS)
> + return;
> +
> + event->hw.flags |= PERF_EVENT_FLAG_USER_READ_CNT;
> +}
> +
> +static void pmu_legacy_event_unmapped(struct perf_event *event, struct mm_struct *mm)
> +{
> + /* In legacy mode, the first 3 CSRs are available. */

same comment

> + if (event->attr.config != PERF_COUNT_HW_CPU_CYCLES &&
> + event->attr.config != PERF_COUNT_HW_INSTRUCTIONS)
> + return;
> +
> + event->hw.flags &= ~PERF_EVENT_FLAG_USER_READ_CNT;
> +}
> +
> /*
> * This is just a simple implementation to allow legacy implementations
> * compatible with new RISC-V PMU driver framework.
> @@ -94,6 +119,9 @@ static void pmu_legacy_init(struct riscv_pmu *pmu)
> pmu->ctr_get_width = NULL;
> pmu->ctr_clear_idx = NULL;
> pmu->ctr_read = pmu_legacy_read_ctr;
> + pmu->event_mapped = pmu_legacy_event_mapped;
> + pmu->event_unmapped = pmu_legacy_event_unmapped;
> + pmu->csr_index = pmu_legacy_csr_index;
>
> perf_pmu_register(&pmu->pmu, RISCV_PMU_LEGACY_PDEV_NAME, PERF_TYPE_RAW);
> }
> --
> 2.37.2
>

Otherwise,

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>