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Subjectperf AppImage - perf stat fails to count child process
Date
Hey all,

because many people only have a pretty outdated perf userspace toolsuite
available, I would like to package a recent version of perf into an AppImage.
My current .travis.yml can be found at [1], the result is available from [2],
e.g. [3].

[1]: https://github.com/milianw/linux/blob/wip/perf-appimage/.travis.yml
[2]: https://travis-ci.org/milianw/linux/
[3]: https://transfer.sh/IX3zr/perf-git.5b330557-x86_64.AppImage

This was build on a Ubuntu 14.04 VM using Travis CI. All libs that got bundled
are those available on that system, except for elfutils - for that I used a
custom build of the newer 0.170 release.

So far so good, this actually seems to work for most purposes I've tried so
far. What's missing is proper `man` integration, I'll try to look into this.
But one issue that I've found which is puzzling me is the following:

perf stat does not work when filtering on an application. I.e. when I use the
system wide mode, it works fine:

~~~~~
$ ./perf-git.3a73b7f9-x86_64.AppImage stat
^C
Performance counter stats for 'system wide':

4510.197963 cpu-clock (msec) # 3.998 CPUs utilized
205 context-switches # 0.045 K/sec
3 cpu-migrations # 0.001 K/sec
0 page-faults # 0.000 K/sec
16,396,597 cycles # 0.004 GHz
13,065,398 stalled-cycles-frontend # 79.68% frontend cycles
idle
11,340,112 stalled-cycles-backend # 69.16% backend cycles
idle
5,718,881 instructions # 0.35 insn per cycle
# 2.28 stalled cycles
per insn
1,197,336 branches # 0.265 M/sec
101,136 branch-misses # 8.45% of all branches

1.128056669 seconds time elapsed
~~~~~

But when I launch an application most counters are empty:

~~~~~
$ ./perf-git.3a73b7f9-x86_64.AppImage stat sleep 1

Performance counter stats for 'sleep 1':

<not counted> task-clock
<not counted> context-switches
<not counted> cpu-migrations
<not counted> page-faults
<not counted> cycles
<not counted> stalled-cycles-frontend
<not counted> stalled-cycles-backend
68,696 instructions
13,573 branches # 0.000 K/sec
1,410 branch-misses # 10.39% of all branches

0.000023100 seconds time elapsed
~~~~~

Also note how this did _not_ sleep for one second but rather quit sooner than
that?!

Stracing (as root, due to AppImage), shows the following issue:

~~~~~
$ sudo strace -f -e fork,execve -s 1000 ./perf-git.3a73b7f9-x86_64.AppImage
stat sleep 1
execve("./perf-git.3a73b7f9-x86_64.AppImage", ["./perf-git.3a73b7f9-
x86_64.AppImage", "stat", "sleep", "1"], 0x7ffea0ec02d0 /* 18 vars */) = 0
strace: Process 21593 attached
strace: Process 21595 attached
[pid 21593] +++ exited with 0 +++
[pid 21592] --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=21593,
si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
strace: Process 21596 attached
[pid 21592] execve("/tmp/.mount_perf-ggA4YJW/AppRun", ["./perf-git.3a73b7f9-
x86_64.AppImage", "stat", "sleep", "1"], 0x1ce1b70 /* 21 vars */) = 0
strace: Process 21597 attached
[pid 21597] execve("/usr/libexec/perf-core/sleep", ["sleep", "1"], 0x3075650 /
* 22 vars */) = -1 ENOENT (No such file or directory)
[pid 21597] execve("/tmp/./sleep", ["sleep", "1"], 0x3075650 /* 22 vars */) =
-1 ENOENT (No such file or directory)
[pid 21597] execve("/home/milian/.bin/sleep", ["sleep", "1"], 0x3075650 /* 22
vars */) = -1 ENOENT (No such file or directory)
[pid 21597] execve("/usr/lib/icecream/libexec/icecc/bin/sleep", ["sleep",
"1"], 0x3075650 /* 22 vars */) = -1 ENOENT (No such file or directory)
[pid 21597] execve("/ssd2/milian/projects/compiled/other/bin/sleep", ["sleep",
"1"], 0x3075650 /* 22 vars */) = -1 ENOENT (No such file or directory)
[pid 21597] execve("/home/milian/.bin/kf5/sleep", ["sleep", "1"], 0x3075650 /*
22 vars */) = -1 ENOENT (No such file or directory)
[pid 21597] execve("/ssd2/milian/projects/compiled/kf5/bin/sleep", ["sleep",
"1"], 0x3075650 /* 22 vars */) = -1 ENOENT (No such file or directory)
[pid 21597] execve("/home/milian/projects/compiled/other/bin/sleep", ["sleep",
"1"], 0x3075650 /* 22 vars */) = -1 ENOENT (No such file or directory)
[pid 21597] execve("/home/milian/projects/compiled/kf5/bin/sleep", ["sleep",
"1"], 0x3075650 /* 22 vars */) = -1 ENOENT (No such file or directory)
[pid 21597] execve("/usr/local/sbin/sleep", ["sleep", "1"], 0x3075650 /* 22
vars */) = -1 ENOENT (No such file or directory)
[pid 21597] execve("/usr/local/bin/sleep", ["sleep", "1"], 0x3075650 /* 22
vars */) = -1 ENOENT (No such file or directory)
[pid 21597] execve("/usr/bin/sleep", ["sleep", "1"], 0x3075650 /* 22 vars */
Performance counter stats for 'sleep 1':

<not counted> task-clock
<not counted> context-switches
<not counted> ) = 0
cpu-migrations
<not counted> page-faults
<not counted> cycles
<not counted> instructions
<not counted> branches
<not counted> branch-misses

0.000033074 seconds time elapsed

Some events weren't counted. Try disabling the NMI watchdog:
echo 0 > /proc/sys/kernel/nmi_watchdog
perf stat ...
echo 1 > /proc/sys/kernel/nmi_watchdog
[pid 21597] --- SIGTERM {si_signo=SIGTERM, si_code=SI_USER, si_pid=21592,
si_uid=0} ---
[pid 21597] +++ killed by SIGTERM +++
[pid 21592] --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_KILLED, si_pid=21597,
si_uid=0, si_status=SIGTERM, si_utime=0, si_stime=0} ---
[pid 21596] --- SIGPIPE {si_signo=SIGPIPE, si_code=SI_USER, si_pid=21595,
si_uid=0} ---
[pid 21592] +++ exited with 0 +++
[pid 21595] --- SIGHUP {si_signo=SIGHUP, si_code=SI_USER, si_pid=21595,
si_uid=0} ---
[pid 21596] +++ exited with 0 +++
+++ exited with 0 +++
~~~~~

I couldn't yet find a way to get a backtrace to the SIGTERM. I also wonder why
I don't see any error message anywhere...

To make this even more confusing, extracting to AppImage (it's essentially a
squashfs image that gets loop-mounted via fuse), things start to work
again...:

~~~~~
$ ./perf-git.3a73b7f9-x86_64.AppImage --appimage-extract
..
$ ./squashfs-root/AppRun stat sleep 1

Performance counter stats for 'sleep 1':

0.559792 task-clock (msec) # 0.001 CPUs utilized
1 context-switches # 0.002 M/sec
0 cpu-migrations # 0.000 K/sec
60 page-faults # 0.107 M/sec
922,471 cycles # 1.648 GHz
564,261 stalled-cycles-frontend # 61.17% frontend cycles
idle
441,173 stalled-cycles-backend # 47.83% backend cycles
idle
743,424 instructions # 0.81 insn per cycle
# 0.76 stalled cycles
per insn
145,166 branches # 259.321 M/sec
7,726 branch-misses # 5.32% of all branches

1.001073810 seconds time elapsed
~~~~~~

So clearly, it has something to do with the FUSE mounting / AppImage... But
has anyone a clue what could be going on here exactly? Any suggestions for
what to try in order to debug this?

Thanks
--
Milian Wolff | milian.wolff@kdab.com | Senior Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt Experts[unhandled content-type:application/pkcs7-signature]
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