Linux 为什么 perf 不报告缓存未命中？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/14674463/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Why doesn't perf report cache misses?
提问by static_rtti
According to perf tutorials, perf statis supposed to report cache misses using hardware counters. However, on my system (up-to-date Arch Linux), it doesn't:
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
What am I missing? I already searched the man page and the web, but didn't find anything obvious.
我错过了什么？我已经搜索了手册页和网络，但没有找到任何明显的东西。
Edit: my CPU is an Intel i5 2300K, if that matters.
编辑：如果重要的话，我的 CPU 是 Intel i5 2300K。
采纳答案by amdn
On my system, an Intel Xeon X5570 @ 2.93 GHzI was able to get perf statto report cache references and misses by requesting those events explicitly like this
在我的系统上，Intel Xeon X5570 @ 2.93 GHz我能够perf stat通过像这样明确请求这些事件来报告缓存引用和未命中
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
The default set of events did not include cache events, matching your results, I don't know why
默认的事件集不包括缓存事件，匹配你的结果，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
回答by SamGamgee
I've spent some minutes trying to understand perf. I found out the cache-misses by first recording and then reporting the data (both perftools).
我花了几分钟试图理解perf. 我通过首先记录然后报告数据（两种perf工具）发现了缓存未命中。
To see a list of events:
要查看事件列表：
perf list
For example, in order to check the last-level-cache load misses, you will need to use the event LLC-loads-misseslike this
例如，为了检查最后一级缓存加载未命中，你将需要使用的情况下LLC-loads-misses这样
perf record -e LLC-loads-misses ./your_program
then report the results
然后报告结果
perf report -v
回答by acgtyrant
In the latest source code, the default event does not include cache-missesand cache-referencesagain:
在最新的源代码中，默认事件不包括cache-misses并cache-references再次：
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 },
};
So the man and most web are out of date as so far.
所以到目前为止，人和大多数网络都已经过时了。
