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Full Discussion: semaphore access speed
Top Forums Programming semaphore access speed Post 302238478 by otheus on Saturday 20th of September 2008 08:26:43 AM
Old 09-20-2008
Quote:
Originally Posted by migurus
Jim,
I never tried profiling before, so I ran into some problem here:
$ gcc -pg -o tstloop tstloop.c
$ tstloop
128205.13 semop/s [0,0]
$ gprof tstloop
gprof: gmon.out file is missing call-graph data
That's strange. Any chance you're running a different program that's elsewhere in the path? Try for instance running "./tstloop".

Also, for gprof, use the -l option (small L). I get:

Code:
$ gprof -l  ./semget
Flat profile:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total
 time   seconds   seconds    calls  Ts/call  Ts/call  name
 57.10      0.13     0.13                             main (semget.c:21 @ 80485f0)
 25.12      0.18     0.06                             main (semget.c:18 @ 804861f)
  9.14      0.20     0.02                             main (semget.c:17 @ 8048614)
  6.85      0.22     0.02                             main (semget.c:16 @ 80485e4)

Line 21 is the semctl() function. Line 18 is the semget() call.

Now that we have concrete results, I'd cross-post this on the Linuxquestions.org com site.

The next step would be to use the debug/profiling version of libc (which I don't have floating around) and see if we can use gprof to find the bottleneck therein. Or, look at the source. It would seem to be of great benefit to have this improved.
 

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MONCONTROL(3)						   BSD Library Functions Manual 					     MONCONTROL(3)

NAME
moncontrol, monstartup -- control execution profile SYNOPSIS
moncontrol(int mode); monstartup(u_long *lowpc, u_long *highpc); DESCRIPTION
An executable program compiled using the -pg option to cc(1) automatically includes calls to collect statistics for the gprof(1) call-graph execution profiler. In typical operation, profiling begins at program startup and ends when the program calls exit. When the program exits, the profiling data are written to the file gmon.out, then gprof(1) can be used to examine the results. moncontrol() selectively controls profiling within a program. When the program starts, profiling begins. To stop the collection of his- togram ticks and call counts use moncontrol(0); to resume the collection of histogram ticks and call counts use moncontrol(1). This feature allows the cost of particular operations to be measured. Note that an output file will be produced on program exit regardless of the state of moncontrol(). Programs that are not loaded with -pg may selectively collect profiling statistics by calling monstartup() with the range of addresses to be profiled. lowpc and highpc specify the address range that is to be sampled; the lowest address sampled is that of lowpc and the highest is just below highpc. Only functions in that range that have been compiled with the -pg option to cc(1) will appear in the call graph part of the output; however, all functions in that address range will have their execution time measured. Profiling begins on return from monstartup(). FILES
gmon.out execution data file SEE ALSO
cc(1), gprof(1), profil(2) 4th Berkeley Distribution June 4, 1993 4th Berkeley Distribution
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