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Memory profiling tools

valgrind

is a way to determine which method is using the most resources in a job.
A valgrind binary is now distributed with LArSoft bundle: you can set it up with setup valgrind v3_13_0 (or the right version: ask ups list -aK+ valgrind). Check out instructions at art wiki as well.

To get the latest version of valgrind (which at the time of writing, 20170808, is 3.13.0), instead, download and install valgrind in your home directory:

# Download valgrind
tar xjvf valgrind-<version>.tar.bz2
cd valgrind-<version>
./configure --prefix=$HOME
make install

This will install valgrind in ~/bin and ~/lib of your account.

Memory leaks

Valgrind is actually a suite of tools. The default tool is memcheck, which hunts for memory leaks:

valgrind `which lar` -c prodgenie.fcl | tee memcheck.txt

Breaking down the above line:

valgrind running valgrind from the current directory (you may need the full valgrind executable path)
`which lar` returns the location of the lar executable as an argument to valgrind
-c prodgenie.fcl typical lar arguments; can be whatever you want
tee memcheck.txt display the output on the screen and write it to file memcheck.txt

Warning: The above command will take many hours or days to execute; valgrind is slow. A better strategy is edit your FHiCL job configuration so you're only executing the particular module in question (e.g. largeant or simwire).

The memcheck tool should also be supported by larrun.sh as larrun.sh --memcheck.

Memory use

If you're looking for which part of your program is using large chunks of memory, the appropriate tool is massif.

valgrind --tool=massif --time-unit=B `which lar` -c prodgenie.fcl | tee massif.txt

This (very slow) process will produce an additional file in the directory from which the command was executed: massif.out.<pid>, where <pid> is the process id of that run of lar. To interpret the contents of this file, use valgrind ms_print utility:
ms_print massif.out.<pid> | less

There is also a handy visualization tool in KDE4 called massif-vistualizer (by now, you will have to use some virtual machine to get it; needless to say, the latest SLF7 is old enough for this).

In comparison with massif, memcheck feels fast.

The script larrun.sh supports massif via --massif option.

As always, one has to understand the precise way the tool works, or be surprised. massif tracks the dynamic (heap) memory allocation performed by new, malloc and friends. They handle the heap as they like, which is usually to book some large chunk of memory (in POSIX and BSD, by mmap) and then they slice it as needed. Even more interesting, the memory free'd or delete'd is not necessarily immediately returned to the operating system. Programs like top and the generic information in the proc filesystem do not descend into this slicing mechanism, and show an amount of memory sensibly larger than the actual requested heap size.

The largest figure in /proc/PID/status (“VmSize”) includes shared libraries, heap, stack and the unused allocated memory all together. massif only talks used heap (and, optionally, stacks).

Execution speed

If one is looking for which portions of the program are being called most often, the appropriate tool is callgrind.

valgrind --tool=callgrind  `which lar` -c prodgenie.fcl | tee callgrind.txt

As with massif, the file callgrind.out.<pid> will be produced. Use callgrind_annotate to interpret this file:
callgrind_annotate callgrind.out.<pid> | less

However, callgrind is the slowest of these tools; for example, if it is run it on a "vanilla" prodgenie.fcl script (which processes 10 events), it will probably take a week to execute. Fortunately, one can obtain a snapshot of the information accumulated by a running instance of callgrind. First, find the process id (pid):

ps -u $USER | grep callgrind

The first number is the pid. Then use callgrind_control to get a snapshot:
callgrind_control <pid> --dump
ls -blarth callgrind.*

One will see a callgrind.out.<pid>.N file on which one can run callgrind_annotate.
For KDE, a kcachegrind is available which has some pitfalls but is still invaluable in navigating the plenty of information from callgrind (and, you may guess, cachegrind).

Do not take callgrind at face value: valgrind is a CPU emulator, and it may grossly overestimate parts of the execution time by ignoring optimisations and tricks your particular CPU may be using. The best way to identify the slowest part of a job is via a sample profiler. callgrind may be useful to explore the flow of the execution though, and sometimes it can point to a code line inside a function which takes lot of time to execute (but again, it may very well be wrong).

dhap tool

Another heap analyser. Not tested yet.
It should be supported as larrun.sh --dhap.

Ignominous Profiler (igprof)

  • open source
  • mature
  • does not require recompilation for simple memory usage monitoring
  • requires injection of markers in the code to trigger detailed memory mapping
  • can profile CPU time instead of memory

Instructions to obtain it are available (so far, for Linux only).
The detailed memory mapping must be triggered. This makes the tool complementary to, for example, valgrind.
We can get a snapshot at precisely the point we want, but we can't find out where precisely we want it.

MemoryTracker - art module

Memory tracker is a art service provided with the art distribution. It writes its detailed information into a SQL database, that can be later unrolled and analysed.
It is documented in art wiki.


For questions, contact Gianluca Petrillo.