perf_event_open: Invalid argument

[dbeniamine]

Hello,

I'm trying to run Mitos on an Intel machine, I manage to install both Dyninst
and Mitos but when I run a command with Mitos I got the following output:

mitosrun ./examples/matmul 
perf_event_open: Invalid argument
Not ready to begin sampling!
6.47073e+07
Segmentation fault

Obviously matmul does not segfault without mitos.

I've run mitos under strace to identify the faulty arguments:

strace mitosrun ./examples/matmul 2>&1 | grep perf_event
read(6, "8:perf_event:/\n7:blkio:/\n6:net_c"..., 1024) = 138
perf_event_open(0x7f51d322d148, 3613, -1, -1, 0) = -1 EINVAL (Invalid argument)
write(2, "perf_event_open: Invalid argumen"..., 34perf_event_open: Invalid argument

But according to the documentation this seems to be right ...
I've also tryed to put the pid argument at -1 and to add the
PERF_FLAG_FD_NO_GROUP without any results ...

Any idea on what can be wrong ?

I'm running debian jessie with a linux kernel 3.16.0-4-amd64 on an Intel
xeon E5520 8 cores processor.

Thanks,
David

[alfredo-gimenez]

Right now Mitos sets up the event encoding for SandyBridge and IvyBridge processors, and looks like you're on a Nehalem processor. From https://software.intel.com/sites/default/files/m/5/2/c/f/1/30320-Nehalem-PMU-Programming-Guide-Core.pdf it looks like the raw event encoding should be 0x100B instead of 0x5101CD . Also see https://lkml.org/lkml/2010/12/22/24 .

The raw event encoding is set here: https://github.com/LLNL/Mitos/blob/master/src/perfsmpl.cpp#L82 .

Could you try changing the encoding? There might be some additional tweaks needed.

[dbeniamine]

Thanks, the fix seems to work.Still when I launch Mitos several times (on a loop), it does not manage to create its traces directorys

Command completed! Processing samples...

Done!

Mitos: Failed to create output directories!
Mitos: Failed to create output directories!
Mitos: Failed to create output directories!
Mitos: Failed to create output directories!

While there is still plenty of space on the drive:

root@edel-24:/tmp# df -h
Filesystem                                 Size  Used Avail Use% Mounted on
/dev/sda5                                   33G   64M   32G   1% /tmp

May it be an issue with the way mitos choose its directories name ?

[alfredo-gimenez]

When you say you launch Mitos several times, what exactly are you doing? Unfortunately you cannot run two samplers simultaneously, there are limits on the performance monitoring units. It also may be a bug in the creation of output directories, they use timestamps and are not necessarily guaranteed to be unique.

[dbeniamine]

I mean on a for loop like:

for b in ./bin/*
do
    mitosrun $b
done

I'll try to add a few second sleep or do file renaming to avoid conflicts.

[alfredo-gimenez]

Ah I see. I'll keep the issue open so I remember to detect Nehalem and issue the correct encoding. Thanks!

[dbeniamine]

After a small test I confirm that renaming mitos directories fix the Failed to create output directories! issue.

Thanks for your help