Why doesn't perf report cache misses?
Solution 1
On my system, an Intel Xeon X5570 @ 2.93 GHz
I was able to get perf stat
to report cache references and misses by requesting those events explicitly like this
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
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
Solution 2
In the latest source code, the default event does not include cache-misses
and cache-references
again:
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So the man and most web are out of date as so far.
Solution 3
I've spent some minutes trying to understand perf
. I found out the cache-misses by first recording and then reporting the data (both perf
tools).
To see a list of events:
perf list
For example, in order to check the last-level-cache load misses, you will need to use the event LLC-loads-misses
like this
perf record -e LLC-loads-misses ./your_program
then report the results
perf report -v
static_rtti
Creator of autojump, the fastest way to move around your filesystem from the command line.
Updated on August 15, 2020Comments
-
static_rtti over 3 years
According to perf tutorials,
perf stat
is supposed to report cache misses using hardware counters. However, on my system (up-to-date Arch Linux), it doesn't:[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.
Edit: my CPU is an Intel i5 2300K, if that matters.