Re: gcj jit, timing comparison

[Andrew Haley <aph at redhat dot com>]

Thomas Johnsson writes:
 > 
 > I'm toying with gcj jit, ie running gcj as a jit:er for gij -- great stuff!
 > For embedded caffeinemark it is called like this:
 > 
 >     $GIJ -Dgnu.gcj.jit.compiler=$GCJ -Dgnu.gcj.jit.cachedir=${CACHEDIR} 
 > -Dgnu.gcj.jit.options=$OPT CaffeineMarkEmbeddedApp
 > (OPT=-O2)
 > 
 > I've run this both for gcj/gij 4.0.2 and 4.1.0, and statically compiled 
 > gcj, with the following numbers:
 > 
 > gij/gcj 'jit' 4.0.2:  39000-39300
 > gij/gcj 'jit' 4.1.0:  44700-44900 
 > gcj -O2 static 4.1.0: 56700-57200
 > 
 > Ie, there's an improvement by about 14%  4.0.2->4.1.0, presumably due to 
 > better code from gcc/gcj. (?)
 > 
 > And now to my question: where does the difference 'jit' vs static come from?

Indirect dispatch, mostly.

 > It is interesting to look at the cache after the run: The .so files are 
 > about 10 times bigger than the .class files.

Try using `strip' on those files.  They'll still be bigger than the
.class files, though: .class is a very efficient encoding.

Andrew.