Hi all,
There is a bug in libpfm4.7.0 and perf on ARM Juno 64bit
Here are some details.
uname -a
Linux juno-1 4.3.0-rc2 #1 SMP Wed Sep 23 15:51:12 CEST 2015 aarch64
aarch64 aarch64 GNU/Linux
cat /proc/cpuinfo
processor : 0
Features : fp asimd evtstrm aes pmull sha1 sha2 crc32
CPU implementer : 0x41
CPU architecture: 8
CPU variant : 0x1
CPU part : 0xd07
CPU revision : 1
processor : 2
Features : fp asimd evtstrm aes pmull sha1 sha2 crc32
CPU implementer : 0x41
CPU architecture: 8
CPU variant : 0x0
CPU part : 0xd03
CPU revision : 3
Processor 0 and 1 are Cortex A57; Processor 2, 3, 4 and 5 are Cortex A53.
Problem: Perfmon and perf report null values if application is moved
between cores while executing.
Steps to reproduce the problem:
exp1: Execute "./syst" (which provides systemwide profiling) available
under /perf_examples, /and observe that the first reading is a garbage
value and the subsequent readings are 0.
(let's assume the system isn't doing any work. in theory, it is not
possible because the kernel is doing something! and perfmon should
report something)
exp2: Run a stress microbenchmark doing only computations pinned to core
0 (taskset -pc 0 <stress_pid>) , "./syst" does have a variability on
core 0 only. This is expected based on the result observed from the
first experiment (refer exp1).
exp3: Move the stress_pid to say... core 2 (taskset -pc 2 <stress_pid>)
while the session of "./syst" is still active, the readings on core 0
AND 2 are 0. Which is not expected behavior as I would expect core 2 to
report performance statistics for that core. On the other hand, if I
restart "./syst", it does report correct readings on core 2 as expected.
I investigated a little further and checked that it is not an issue that
core 2 is A53, and core 0 is A57; because even if I moved stress_pid in
exp2 to core 1, it still fails.
I also tried pinning "./syst" to a given core type and ran stress_pid,
only a given core in that coretype. It still reports a null value if I
move the pid to a different core in the same coretype.
Btw, this happens also if I specify the pid of the application, that is
PerThreadMonitoring using "./task_cpu".
The exact same issues were found with "perf".
is it a known bug?
Any help will be appreciated.
Best Regards,
Rajiv Nishtala
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