[英]Why doesn't perf report cache misses?
根据perf教程 , perf stat
应该使用硬件计数器报告缓存未命中。 但是,在我的系统(最新的Arch Linux)上,它没有:
[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
我错过了什么? 我已经搜索了手册页和网页,但没有找到任何明显的东西。
编辑:我的CPU是英特尔i5 2300K,如果这很重要。
在我的系统中, Intel Xeon X5570 @ 2.93 GHz
我能得到perf stat
通过请求这些事件报告的高速缓存引用和未明确这样
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
默认的事件集不包括缓存事件,匹配您的结果,我不知道为什么
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
在最新的源代码中 ,默认事件不再包括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 },
};
所以到目前为止,男人和大多数网络已经过时了。
我花了几分钟试图理解perf
。 我通过首先记录然后报告数据(两个perf
工具)找到了缓存未命中。
要查看事件列表:
perf list
例如,为了检查最后一级缓存加载未命中,您需要使用事件LLC-loads-misses
miss这样的
perf record -e LLC-loads-misses ./your_program
然后报告结果
perf report -v
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