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Subject[PATCH] arm_pmu: Fix write counter incorrect in ARMv7 big-endian mode
Date
Commit 3a95200d3f89a ("arm_pmu: Change API to support 64bit counter values")
changes the input "value" type from 32-bit to 64-bit,
which introduces the following problem:
ARMv7 PMU counters is 32-bit width, in big-endian mode, write counter uses
high 32-bit, which writes an incorrect value.

Before:

Performance counter stats for 'ls':

2.22 msec task-clock # 0.675 CPUs utilized
0 context-switches # 0.000 K/sec
0 cpu-migrations # 0.000 K/sec
49 page-faults # 0.022 M/sec
2150476593 cycles # 966.663 GHz
2148588788 instructions # 1.00 insn per cycle
2147745484 branches # 965435.074 M/sec
2147508540 branch-misses # 99.99% of all branches

None of the above hw event counters are correct.

Solution:

"value" forcibly converted to 32-bit type before being written to PMU register.

After:

Performance counter stats for 'ls':

2.09 msec task-clock # 0.681 CPUs utilized
0 context-switches # 0.000 K/sec
0 cpu-migrations # 0.000 K/sec
46 page-faults # 0.022 M/sec
2807301 cycles # 1.344 GHz
1060159 instructions # 0.38 insn per cycle
250496 branches # 119.914 M/sec
23192 branch-misses # 9.26% of all branches

Fixes: 3a95200d3f89a ("arm_pmu: Change API to support 64bit counter values")
Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
---
arch/arm/kernel/perf_event_v7.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/perf_event_v7.c b/arch/arm/kernel/perf_event_v7.c
index 2924d7910b10..eb2190477da1 100644
--- a/arch/arm/kernel/perf_event_v7.c
+++ b/arch/arm/kernel/perf_event_v7.c
@@ -773,10 +773,10 @@ static inline void armv7pmu_write_counter(struct perf_event *event, u64 value)
pr_err("CPU%u writing wrong counter %d\n",
smp_processor_id(), idx);
} else if (idx == ARMV7_IDX_CYCLE_COUNTER) {
- asm volatile("mcr p15, 0, %0, c9, c13, 0" : : "r" (value));
+ asm volatile("mcr p15, 0, %0, c9, c13, 0" : : "r" ((u32)value));
} else {
armv7_pmnc_select_counter(idx);
- asm volatile("mcr p15, 0, %0, c9, c13, 2" : : "r" (value));
+ asm volatile("mcr p15, 0, %0, c9, c13, 2" : : "r" ((u32)value));
}
}

--
2.30.GIT
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