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

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Message-Id: <20250804025110.11088-1-cuiyunhui@bytedance.com>
Date: Mon,  4 Aug 2025 10:51:10 +0800
From: Yunhui Cui <cuiyunhui@...edance.com>
To: atish.patra@...ux.dev,
	anup@...infault.org,
	will@...nel.org,
	mark.rutland@....com,
	paul.walmsley@...ive.com,
	palmer@...belt.com,
	aou@...s.berkeley.edu,
	alex@...ti.fr,
	linux-riscv@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Yunhui Cui <cuiyunhui@...edance.com>
Subject: [PATCH] perf: riscv: skip empty batches in counter start

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@...edance.com>
---
 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