关于概要分析：无法使用linux perf采样硬件高速缓存事件

Can't sample hardware cache events with linux perf

由于某些原因，我无法采样(perf record)硬件缓存事件：

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# perf record -e L1-dcache-stores -a -c 100 -- sleep 5
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.607 MB perf.data (~26517 samples) ]
# perf script

但我可以算出它们(perf stat)：

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# perf stat -e L1-dcache-stores -a -- sleep 5
Performance counter stats for 'sleep 5':

711,781 L1-dcache-stores

5.000842990 seconds time elapsed

我尝试使用不同的CPU，OS版本(和内核版本)，perf版本，但是结果是相同的。这是预期的行为吗？是什么原因？ perf不能对此发出警告吗？

相关讨论

perf evlist -vvv输出的三个性能数据有所不同，三个是缓存事件，第二个软件事件和最后一个硬件周期事件：

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echo '2^234567 %2' | perf record -e L1-dcache-stores -c 100 -o cache bc
echo '2^234567 %2' | perf record -e cycles -c 100 -o cycles bc
echo '2^234567 %2' | perf record -e cs -c 100 -o cs bc

perf evlist -vvv -i cache
L1-dcache-stores: sample_freq=100, type: 3, config: 256, size: 96, sample_type: IP|TID|TIME, disabled: 1, inherit: 1, mmap: 1, mmap2: 1, comm: 1, enable_on_exec: 1, sample_id_all: 1, exclude_guest: 1
perf evlist -vvv -i cycles
cycles: sample_freq=100, size: 96, sample_type: IP|TID|TIME, disabled: 1, inherit: 1, mmap: 1, mmap2: 1, comm: 1, enable_on_exec: 1, sample_id_all: 1, exclude_guest: 1
perf evlist -vvv -i cs
cs: sample_freq=100, type: 1, config: 3, size: 96, sample_type: IP|TID|TIME, disabled: 1, inherit: 1, mmap: 1, mmap2: 1, comm: 1, enable_on_exec: 1, sample_id_all: 1, exclude_guest: 1

有不同的类型，并且类型定义为

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0028 enum perf_type_id {
0029 PERF_TYPE_HARDWARE = 0,
0030 PERF_TYPE_SOFTWARE = 1,
0031 PERF_TYPE_TRACEPOINT = 2,
0032 PERF_TYPE_HW_CACHE = 3,
0033 PERF_TYPE_RAW = 4,
0034 PERF_TYPE_BREAKPOINT = 5,
0035
0036 PERF_TYPE_MAX, /* non-ABI */
0037 };

Perf脚本具有一个output表，该表定义了如何打印各种事件：http://lxr.free-electrons.com/source/tools/perf/builtin-script.c?v=3.16#L68

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68 /* default set to maintain compatibility with current format */
69 static struct {
70 bool user_set;
71 bool wildcard_set;
72 unsigned int print_ip_opts;
73 u64 fields;
74 u64 invalid_fields;
75 } output[PERF_TYPE_MAX] = {
76
77 [PERF_TYPE_HARDWARE] = {
78 .user_set = false,
79
80 .fields = PERF_OUTPUT_COMM | PERF_OUTPUT_TID |
81 PERF_OUTPUT_CPU | PERF_OUTPUT_TIME |
82 PERF_OUTPUT_EVNAME | PERF_OUTPUT_IP |
83 PERF_OUTPUT_SYM | PERF_OUTPUT_DSO,
84
85 .invalid_fields = PERF_OUTPUT_TRACE,
86 },
87
88 [PERF_TYPE_SOFTWARE] = {
89 .user_set = false,
90
91 .fields = PERF_OUTPUT_COMM | PERF_OUTPUT_TID |
92 PERF_OUTPUT_CPU | PERF_OUTPUT_TIME |
93 PERF_OUTPUT_EVNAME | PERF_OUTPUT_IP |
94 PERF_OUTPUT_SYM | PERF_OUTPUT_DSO,
95
96 .invalid_fields = PERF_OUTPUT_TRACE,
97 },
98
99 [PERF_TYPE_TRACEPOINT] = {
100 .user_set = false,
101
102 .fields = PERF_OUTPUT_COMM | PERF_OUTPUT_TID |
103 PERF_OUTPUT_CPU | PERF_OUTPUT_TIME |
104 PERF_OUTPUT_EVNAME | PERF_OUTPUT_TRACE,
105 },
106
107 [PERF_TYPE_RAW] = {
108 .user_set = false,
109
110 .fields = PERF_OUTPUT_COMM | PERF_OUTPUT_TID |
111 PERF_OUTPUT_CPU | PERF_OUTPUT_TIME |
112 PERF_OUTPUT_EVNAME | PERF_OUTPUT_IP |
113 PERF_OUTPUT_SYM | PERF_OUTPUT_DSO,
114
115 .invalid_fields = PERF_OUTPUT_TRACE,
116 },
117 };
118

因此，没有说明从类型3的样本中打印任何字段-PERF_TYPE_HW_CACHE，并且perf script不打印它们。我们可以尝试在output数组中注册此类型，甚至将补丁推入内核。