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Subject[PATCH 5/8] ARCv2: perf: set usable max period as a half of real max period
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From: Alexey Brodkin <abrodkin@synopsys.com>

Overflow interrupt happens when counter reaches a limit which we set as a
maximum value of the counter.

But for better precision counter continues registration of assigned events
even after reaching pre-defined limit. To not really overlap we leave half
of the counter values free.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
---
arch/arc/kernel/perf_event.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arc/kernel/perf_event.c b/arch/arc/kernel/perf_event.c
index 4e3211948467..a7b4e4826533 100644
--- a/arch/arc/kernel/perf_event.c
+++ b/arch/arc/kernel/perf_event.c
@@ -491,7 +491,7 @@ static int arc_pmu_device_probe(struct platform_device *pdev)
arc_pmu->n_counters = pct_bcr.c;
counter_size = 32 + (pct_bcr.s << 4);

- arc_pmu->max_period = (1ULL << counter_size) - 1ULL;
+ arc_pmu->max_period = (1ULL << counter_size) / 2 - 1ULL;

pr_info("ARC perf\t: %d counters (%d bits), %d conditions%s\n",
arc_pmu->n_counters, counter_size, cc_bcr.c,
--
1.9.1


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