[PATCH] perf: riscv: skip empty batches in counter start

[Anup Patel]

On Mon, Aug 4, 2025 at 8:21 AM Yunhui Cui <cuiyunhui at bytedance.com> wrote:
>
> Avoid unnecessary SBI calls when starting non-overflowed counters
> in pmu_sbi_start_ovf_ctrs_sbi() by checking ctr_start_mask.
>
> Signed-off-by: Yunhui Cui <cuiyunhui at bytedance.com>

LGTM.

Reviewed-by: Anup Patel <anup at brainfault.org>

Regards,
Anup

> ---
>  drivers/perf/riscv_pmu_sbi.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
> index 698de8ddf895b..3977f7488e4ef 100644
> --- a/drivers/perf/riscv_pmu_sbi.c
> +++ b/drivers/perf/riscv_pmu_sbi.c
> @@ -877,8 +877,10 @@ static inline void pmu_sbi_start_ovf_ctrs_sbi(struct cpu_hw_events *cpu_hw_evt,
>         for (i = 0; i < BITS_TO_LONGS(RISCV_MAX_COUNTERS); i++) {
>                 ctr_start_mask = cpu_hw_evt->used_hw_ctrs[i] & ~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, i * BITS_PER_LONG, ctr_start_mask,
> -                       0, 0, 0, 0);
> +               if (ctr_start_mask) {
> +                       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 */
> --
> 2.39.5
>