4.4. What's in a profiling report?

When you run your profiled program with the -p RTS option , you get the following information about your “cost centres”:

COST CENTRE:

The cost-centre's name.

MODULE:

The module associated with the cost-centre; important mostly if you have identically-named cost-centres in different modules.

scc:

How many times this cost-centre was entered; think of it as “I got to the _scc_ construct this many times…”

%time:

What part of the time was spent in this cost-centre (see also “ticks,” below).

%alloc:

What part of the memory allocation was done in this cost-centre (see also “bytes,” below).

inner:

How many times this cost-centre “passed control” to an inner cost-centre; for example, scc=4 plus subscc=8 means “This _scc_ was entered four times, but went out to other _scc_s eight times.”

cafs:

How many CAFs this cost centre evaluated.

dicts:

How many dictionaries this cost centre evaluated.

In addition you can use the -P RTS option to get the following additional information:

ticks:

The raw number of time “ticks” which were attributed to this cost-centre; from this, we get the %time figure mentioned above.

bytes:

Number of bytes allocated in the heap while in this cost-centre; again, this is the raw number from which we get the %alloc figure mentioned above.

Finally if you built your program with -prof-details the -P RTS option will also produce the following information:

closures:

How many heap objects were allocated; these objects may be of varying size. If you divide the number of bytes (mentioned below) by this number of “closures”, then you will get the average object size. (Not too interesting, but still…)

thunks:

How many times we entered (evaluated) a thunk—an unevaluated object in the heap—while we were in this cost-centre.

funcs:

How many times we entered (evaluated) a function while we we in this cost-centre. (In Haskell, functions are first-class values and may be passed as arguments, returned as results, evaluated, and generally manipulated just like data values)

PAPs:

How many times we entered (evaluated) a partial application (PAP), i.e., a function applied to fewer arguments than it needs. For example, Int addition applied to one argument would be a PAP. A PAP is really just a particular form for a function.