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From:   Yury Norov <yury.norov@gmail.com>
To:     linux-kernel@vger.kernel.org,
        Shuai Xue <xueshuai@linux.alibaba.com>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        linux-arm-kernel@lists.infradead.org
Cc:     Yury Norov <yury.norov@gmail.com>, Jan Kara <jack@suse.cz>,
        Mirsad Todorovac <mirsad.todorovac@alu.unizg.hr>,
        Matthew Wilcox <willy@infradead.org>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@linaro.org>,
        Alexey Klimov <klimov.linux@gmail.com>
Subject: [PATCH 08/34] drivers/perf: optimize ali_drw_get_counter_idx() by using find_bit()
Date:   Sat, 18 Nov 2023 07:50:39 -0800
Message-Id: <20231118155105.25678-9-yury.norov@gmail.com>
In-Reply-To: <20231118155105.25678-1-yury.norov@gmail.com>
References: <20231118155105.25678-1-yury.norov@gmail.com>
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The function searches used_mask for a set bit in a for-loop bit by bit.
We can do it faster by using atomic find_and_set_bit().

Signed-off-by: Yury Norov <yury.norov@gmail.com>
---
 drivers/perf/alibaba_uncore_drw_pmu.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/drivers/perf/alibaba_uncore_drw_pmu.c b/drivers/perf/alibaba_uncore_drw_pmu.c
index 19d459a36be5..2a3b7701d568 100644
--- a/drivers/perf/alibaba_uncore_drw_pmu.c
+++ b/drivers/perf/alibaba_uncore_drw_pmu.c
@@ -274,15 +274,9 @@ static const struct attribute_group *ali_drw_pmu_attr_groups[] = {
 static int ali_drw_get_counter_idx(struct perf_event *event)
 {
 	struct ali_drw_pmu *drw_pmu = to_ali_drw_pmu(event->pmu);
-	int idx;
+	int idx = find_and_set_bit(drw_pmu->used_mask, ALI_DRW_PMU_COMMON_MAX_COUNTERS);
 
-	for (idx = 0; idx < ALI_DRW_PMU_COMMON_MAX_COUNTERS; ++idx) {
-		if (!test_and_set_bit(idx, drw_pmu->used_mask))
-			return idx;
-	}
-
-	/* The counters are all in use. */
-	return -EBUSY;
+	return idx < ALI_DRW_PMU_COMMON_MAX_COUNTERS ? idx : -EBUSY;
 }
 
 static u64 ali_drw_pmu_read_counter(struct perf_event *event)
-- 
2.39.2