Re: [glob2-devel] Optimization suggestions (Map::updateLocalGradient())

[Erik Søe Sørensen]

Joe Wells skrev:

> By the way, can you please write a short profiling “how to” explaining
> what exact commands you typed to obtain this information?  That would
> be really helpful (because on different machines and/or with different
> configuration options different portions of the code might be the
> worst spots, so it would be nice if other people could easily do the
> same profiling).
>  
For starters, I propose we add a profiling option to the build script :-)

The tools I've used for profiling are:

- gprof - relatively easy to use. Breaks down the runtime into 
functions; this is good for identifying bottlenecks.
In theory, it should be usable for getting information on source line 
level instead of just function level. However, either a) I'm using it 
wrong, or b) it just has to take ages for this size of program,  even if 
you just ask about a single function. (Literally, ages - I guess you 
could progress acouple in Age of Empires :)

- oprofile - just discovered it for this purpose.
This profiling tool is a bit special, in that it monitors the whole 
system - everything that's running on your machine, including (if you 
ask for it) the kernel. For this reason, the monitoring daemon requires 
root acces.
I've used this tool for getting line-level time statistics; if you ask 
for it, it can create copies of the source files annotated with the 
statistics (for each line, function and file).

Things of which to be ware:
- Profile the right thing.
 Profiling an application compiled without optimization (-O3) is useless;
 the optimizations you'll find may just be ones also be found by the 
compiler.
 For this reason, I've let building with profiling also enable 
optimizations (I didn't at first).
- Having a performance-test run mode would help a bit - it would also 
facilitate performance comparisons  :-)

That was the short version. Exact commands? Well, for gprof:
1. Build glob2 with PROFILE=yes.
2. Run glob2, play, have fun.
3. Exit the game. Now a file called 'gmon.out' will be generated.
4. Run gprof: "gprof path/to/glob2 path/to/gmon.out" - and capture the 
output for scrutiny.
   There are command-line options for call-graph analysis (instead of a 
flat function profile), and also for line-profiling (but I haven't 
gotten that to work usefully).

I hope this helps :-)

/Erik

diff --git a/SConstruct b/SConstruct
--- a/SConstruct
+++ b/SConstruct
@@ -5,6 +5,7 @@ def establish_options(env):
     opts.Add("INSTALLDIR", "Installation Directory", "/usr/local/share")
     opts.Add("BINDIR", "Binary Installation Directory", "/usr/local/bin")
     opts.Add(BoolOption("release", "Build for release", 0))
+    opts.Add(BoolOption("profile", 'Build with profiling on', False))
     opts.Add(BoolOption("mingw", "Build with mingw enabled if not 
auto-detected", 0))
     opts.Add(BoolOption("osx", "Build for OSX", 0))
     Help(opts.GenerateHelpText(env))
@@ -136,6 +137,10 @@ def main():
         env.Append(CPPPATH=["C:/msys/1.0/local/include/SDL", 
"C:/msys/1.0/local/include", "C:/msys/1.0/include/SDL", "C:/msys/1.0/include"])
     configure(env)
     env.Append(CPPPATH=['#libgag/include', '#'])
+    if env['profile']:
+        env.Append(CXXFLAGS=' -pg')
+        env.Append(LINKFLAGS='-pg')
+        env.Append(CXXFLAGS=' -O3')
     if env['release']:
         env.Append(CXXFLAGS=' -O3')
     if env['mingw'] or env['PLATFORM'] == 'win32':