Sam: a tiny, concurrent sampling profiler for Clozure Common Lisp

I have recently been in need of a profiler for my favorite Common Lisp implementation, Clozure Common Lisp, but sadly its mechanism for generating a Lisp image for use with oprofile no longer works with recent versions of Linux/oprofile. rme explained it to me in #ccl on Freenode:

“Recent kernels and perf versions are not fooled by our trick of making a heap image look sort of like an ELF file. Also, they only consider mapped memory from ELF files (and not just some random file, like a heap image) as a place where functions can reside.”

That was disappointing, I had waited for the new Slackware release to get a compatible version of libelf, after all. I also looked into the deterministic profiler for CCL by Hans Huebner that lives in contrib/, but that one bit-rotted, sadly.

Still, my search was not in vain. rme sent me a very helpful paste, whose contents he described as “a crude userland-based sampling profiler”. Here is how it works: it peeks into the call stack of a running process repeatedly to find out which function is being run, and counts how often it finds the process busy with a given function. With the collected information it can then report an estimate of where time is spent.

After having given some love to this tiny profiler’s report output, I figured why not share it for others to use, and rme kindly agreed. Meet Sam, it supports profiling forms as well as running processes, and is reasonably well documented. You can use it to profile arbitrary forms like this:

CL-USER> (sam:profile ()
           (loop for i from 1 to 1e8 sum i))
39%  CCL::>-2  <no source>
19%  CCL::FIXNUM-SFLOAT-COMPARE  <no source>
15%  #<Anonymous Function #x30200B10843F>  <no source>
12%  SAM:CALL-WITH-SAMPLING  (defun call-with-sampling (fn ...
11%  CCL::INTEGER-DECODE-SHORT-FLOAT  <no source>
 5%  CCL::FIXNUM-DECODE-SHORT-FLOAT  <no source>

…or profile a different process:

CL-USER> (sam:profile-process (fourth (all-processes)) 1)
100%  CCL::FD-READ  <no source>

May the search engines index this, and spare others from repeating my search (but not from reading about it.) I hope Sam can be of use to you, and let me know if you find any bugs!