why does perf record and annotate not work? - linux

Question

I'm stumped, I read the perf tutorial and am trying to do a simple test beyond "perf stat" which works. However perf record either doesnt work ,or perf annotate shows no samples recorded. Running perf
For example(im running with sudo because without it i get a bunch of errors which i will post at the end):
sudo perf record -e cycles,instructions,cache-misses -a -c 1 ./FooExe
[ perf record: Woken up 4 times to write data ]
[ perf record: Captured and wrote 1.794 MB perf.data (~78393 samples) ]
.
sudo perf report -D -i perf.data |grep RECORD_SAMPLE |wc -l
Failed to open /tmp/perf-23796.map, continuing without symbols
20486
.
sudo perf annotate -d ./FooExe
the perf.data file has no samples! Press any key
So thats as far as i get. I tried to rebuild perf for my ssystem from source but that didnt seem to help either.
Im using Ubuntu 14.04 kernel 3.19.0-49-generic. This is on intel i7 I4510U cpu . I made sure to compile my program with symbols , but i get the same results regardless of which application i try to profile.
-- if i run without sudo :
WARNING: Kernel address maps (/proc/{kallsyms,modules}) are restricted,
check /proc/sys/kernel/kptr_restrict.
Samples in kernel functions may not be resolved if a suitable vmlinux
file is not found in the buildid cache or in the vmlinux path.
Samples in kernel modules won't be resolved at all.
If some relocation was applied (e.g. kexec) symbols may be misresolved
even with a suitable vmlinux or kallsyms file.
Cannot read kernel map
Error:
You may not have permission to collect system-wide stats.
Consider tweaking /proc/sys/kernel/perf_event_paranoid:
-1 - Not paranoid at all
0 - Disallow raw tracepoint access for unpriv
1 - Disallow cpu events for unpriv
2 - Disallow kernel profiling for unpriv

Answer 1

I just tried your command. The problem was that you used -a to profile all processes system-wide, so it never ran ./FooExe. You can confirm this with strace -f perf ... ./FooExe, and note the lack of any execve system call. And also the fact that it returns instantly, even if FooExe should have taken several seconds.
Here's an example of recording samples for a busy-loop awk command:
perf record -e cycles,instructions,cache-misses awk 'BEGIN{for(i=0;i<40000000;i++){}}'
Now perf report works. You don't need to specify the executable for the report command, because perf.data only has data for the one executable.
This works the same way with the ocperf.py wrapper, but you could record events for more uarch-specific events using symbolic names (instead of looking up codes and numeric arguments in -e):
$ ocperf.py record -e cycles,cache-misses,uops_dispatched_port.port_0 awk 'BEGIN{for(i=0;i<40000000;i++){}}'
perf record -e cycles,cache-misses,cpu/event=0xa1,umask=0x1,name=uops_dispatched_port_port_0,period=2000003/ awk 'BEGIN{for(i=0;i<40000000;i++){}}'
(warning lines about kernel symbols)
[ perf record: Woken up 2 times to write data ]
[ perf record: Captured and wrote 0.352 MB perf.data (7819 samples)
$ ocperf.py report