gprof: Flat Profile
5.1 The Flat Profile
====================
The "flat profile" shows the total amount of time your program spent
executing each function. Unless the '-z' option is given, functions
with no apparent time spent in them, and no apparent calls to them, are
not mentioned. Note that if a function was not compiled for profiling,
and didn't run long enough to show up on the program counter histogram,
it will be indistinguishable from a function that was never called.
This is part of a flat profile for a small program:
Flat profile:
Each sample counts as 0.01 seconds.
% cumulative self self total
time seconds seconds calls ms/call ms/call name
33.34 0.02 0.02 7208 0.00 0.00 open
16.67 0.03 0.01 244 0.04 0.12 offtime
16.67 0.04 0.01 8 1.25 1.25 memccpy
16.67 0.05 0.01 7 1.43 1.43 write
16.67 0.06 0.01 mcount
0.00 0.06 0.00 236 0.00 0.00 tzset
0.00 0.06 0.00 192 0.00 0.00 tolower
0.00 0.06 0.00 47 0.00 0.00 strlen
0.00 0.06 0.00 45 0.00 0.00 strchr
0.00 0.06 0.00 1 0.00 50.00 main
0.00 0.06 0.00 1 0.00 0.00 memcpy
0.00 0.06 0.00 1 0.00 10.11 print
0.00 0.06 0.00 1 0.00 0.00 profil
0.00 0.06 0.00 1 0.00 50.00 report
...
The functions are sorted first by decreasing run-time spent in them,
then by decreasing number of calls, then alphabetically by name. The
functions 'mcount' and 'profil' are part of the profiling apparatus and
appear in every flat profile; their time gives a measure of the amount
of overhead due to profiling.
Just before the column headers, a statement appears indicating how
much time each sample counted as. This "sampling period" estimates the
margin of error in each of the time figures. A time figure that is not
much larger than this is not reliable. In this example, each sample
counted as 0.01 seconds, suggesting a 100 Hz sampling rate. The
program's total execution time was 0.06 seconds, as indicated by the
'cumulative seconds' field. Since each sample counted for 0.01 seconds,
this means only six samples were taken during the run. Two of the
samples occurred while the program was in the 'open' function, as
indicated by the 'self seconds' field. Each of the other four samples
occurred one each in 'offtime', 'memccpy', 'write', and 'mcount'. Since
only six samples were taken, none of these values can be regarded as
particularly reliable. In another run, the 'self seconds' field for
'mcount' might well be '0.00' or '0.02'. 
Statistical Sampling
Error Sampling Error, for a complete discussion.
The remaining functions in the listing (those whose 'self seconds'
field is '0.00') didn't appear in the histogram samples at all.
However, the call graph indicated that they were called, so therefore
they are listed, sorted in decreasing order by the 'calls' field.
Clearly some time was spent executing these functions, but the paucity
of histogram samples prevents any determination of how much time each
took.
Here is what the fields in each line mean:
'% time'
This is the percentage of the total execution time your program
spent in this function. These should all add up to 100%.
'cumulative seconds'
This is the cumulative total number of seconds the computer spent
executing this functions, plus the time spent in all the functions
above this one in this table.
'self seconds'
This is the number of seconds accounted for by this function alone.
The flat profile listing is sorted first by this number.
'calls'
This is the total number of times the function was called. If the
function was never called, or the number of times it was called
cannot be determined (probably because the function was not
compiled with profiling enabled), the "calls" field is blank.
'self ms/call'
This represents the average number of milliseconds spent in this
function per call, if this function is profiled. Otherwise, this
field is blank for this function.
'total ms/call'
This represents the average number of milliseconds spent in this
function and its descendants per call, if this function is
profiled. Otherwise, this field is blank for this function. This
is the only field in the flat profile that uses call graph
analysis.
'name'
This is the name of the function. The flat profile is sorted by
this field alphabetically after the "self seconds" and "calls"
fields are sorted.
Info Catalog
gprof: Output
gprof: Call Graph