[英]Why doesn't perf report cache misses?
根據perf教程 , perf stat
應該使用硬件計數器報告緩存未命中。 但是,在我的系統(最新的Arch Linux)上,它沒有:
[joel@panda goog]$ perf stat ./hash
Performance counter stats for './hash':
869.447863 task-clock # 0.997 CPUs utilized
92 context-switches # 0.106 K/sec
4 cpu-migrations # 0.005 K/sec
1,041 page-faults # 0.001 M/sec
2,628,646,296 cycles # 3.023 GHz
819,269,992 stalled-cycles-frontend # 31.17% frontend cycles idle
132,355,435 stalled-cycles-backend # 5.04% backend cycles idle
4,515,152,198 instructions # 1.72 insns per cycle
# 0.18 stalled cycles per insn
1,060,739,808 branches # 1220.015 M/sec
2,653,157 branch-misses # 0.25% of all branches
0.871766141 seconds time elapsed
我錯過了什么? 我已經搜索了手冊頁和網頁,但沒有找到任何明顯的東西。
編輯:我的CPU是英特爾i5 2300K,如果這很重要。
在我的系統中, Intel Xeon X5570 @ 2.93 GHz
我能得到perf stat
通過請求這些事件報告的高速緩存引用和未明確這樣
perf stat -B -e cache-references,cache-misses,cycles,instructions,branches,faults,migrations sleep 5
Performance counter stats for 'sleep 5':
10573 cache-references
1949 cache-misses # 18.434 % of all cache refs
1077328 cycles # 0.000 GHz
715248 instructions # 0.66 insns per cycle
151188 branches
154 faults
0 migrations
5.002776842 seconds time elapsed
默認的事件集不包括緩存事件,匹配您的結果,我不知道為什么
perf stat -B sleep 5
Performance counter stats for 'sleep 5':
0.344308 task-clock # 0.000 CPUs utilized
1 context-switches # 0.003 M/sec
0 CPU-migrations # 0.000 M/sec
154 page-faults # 0.447 M/sec
977183 cycles # 2.838 GHz
586878 stalled-cycles-frontend # 60.06% frontend cycles idle
430497 stalled-cycles-backend # 44.05% backend cycles idle
720815 instructions # 0.74 insns per cycle
# 0.81 stalled cycles per insn
152217 branches # 442.095 M/sec
7646 branch-misses # 5.02% of all branches
5.002763199 seconds time elapsed
在最新的源代碼中 ,默認事件不再包括cache-misses
和cache-references
:
struct perf_event_attr default_attrs[] = {
{ .type = PERF_TYPE_SOFTWARE, .config = PERF_COUNT_SW_TASK_CLOCK },
{ .type = PERF_TYPE_SOFTWARE, .config = PERF_COUNT_SW_CONTEXT_SWITCHES },
{ .type = PERF_TYPE_SOFTWARE, .config = PERF_COUNT_SW_CPU_MIGRATIONS },
{ .type = PERF_TYPE_SOFTWARE, .config = PERF_COUNT_SW_PAGE_FAULTS },
{ .type = PERF_TYPE_HARDWARE, .config = PERF_COUNT_HW_CPU_CYCLES },
{ .type = PERF_TYPE_HARDWARE, .config = PERF_COUNT_HW_STALLED_CYCLES_FRONTEND },
{ .type = PERF_TYPE_HARDWARE, .config = PERF_COUNT_HW_STALLED_CYCLES_BACKEND },
{ .type = PERF_TYPE_HARDWARE, .config = PERF_COUNT_HW_INSTRUCTIONS },
{ .type = PERF_TYPE_HARDWARE, .config = PERF_COUNT_HW_BRANCH_INSTRUCTIONS },
{ .type = PERF_TYPE_HARDWARE, .config = PERF_COUNT_HW_BRANCH_MISSES },
};
所以到目前為止,男人和大多數網絡已經過時了。
我花了幾分鍾試圖理解perf
。 我通過首先記錄然后報告數據(兩個perf
工具)找到了緩存未命中。
要查看事件列表:
perf list
例如,為了檢查最后一級緩存加載未命中,您需要使用事件LLC-loads-misses
miss這樣的
perf record -e LLC-loads-misses ./your_program
然后報告結果
perf report -v
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