gcj jit, timing comparison

[Thomas Johnsson <thomas at gatespacetelematics dot com>]

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?



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

[thomas@lan3 embedded-caffeinemark]$ ls -l gcj-cache
total 292
-rw-r--r--  1 thomas thomas   638 Jun  1 16:48 
1dd84d3c35e7833172c5d1f51bb6fed.class
-rwxrwxr-x  1 thomas thomas  8743 Jun  1 16:48 
1dd84d3c35e7833172c5d1f51bb6fed.so
-rw-r--r--  1 thomas thomas  1322 Jun  1 16:48 
2a5b241774eefb8e1eb2f3054f72e2.class
-rwxrwxr-x  1 thomas thomas 11585 Jun  1 16:48 
2a5b241774eefb8e1eb2f3054f72e2.so
-rw-r--r--  1 thomas thomas   934 Jun  1 16:48 
68554c42c642559d7f4c2e67c0396261.class
-rwxrwxr-x  1 thomas thomas  9284 Jun  1 16:48 
68554c42c642559d7f4c2e67c0396261.so
-rw-r--r--  1 thomas thomas   940 Jun  1 16:48 
6ba8a4b6172958670f6a5b4854dab73.class
-rwxrwxr-x  1 thomas thomas  9443 Jun  1 16:48 
6ba8a4b6172958670f6a5b4854dab73.so
-rw-r--r--  1 thomas thomas   331 Jun  1 16:48 
6f114c50bd994dd8f26519136f9adb9.class
-rwxrwxr-x  1 thomas thomas  5815 Jun  1 16:48 
6f114c50bd994dd8f26519136f9adb9.so
-rw-r--r--  1 thomas thomas  1121 Jun  1 16:48 
85b230da126cd42ed85a3dd69122fdf9.class
-rwxrwxr-x  1 thomas thomas  9741 Jun  1 16:48 
85b230da126cd42ed85a3dd69122fdf9.so
-rw-r--r--  1 thomas thomas   817 Jun  1 16:48 
a7dbaca6d3d6cc37a2b4ce46abd399c8.class
-rwxrwxr-x  1 thomas thomas  9139 Jun  1 16:48 
a7dbaca6d3d6cc37a2b4ce46abd399c8.so
-rw-r--r--  1 thomas thomas   174 Jun  1 16:48 
a8c05719d37f4c5a651aa7c46b54ce8.class
-rwxrwxr-x  1 thomas thomas  5208 Jun  1 16:48 
a8c05719d37f4c5a651aa7c46b54ce8.so
-rw-r--r--  1 thomas thomas  1184 Jun  1 16:48 
c845d4cca661f37a3bd732fadf449ed5.class
-rwxrwxr-x  1 thomas thomas 10465 Jun  1 16:48 
c845d4cca661f37a3bd732fadf449ed5.so
-rw-r--r--  1 thomas thomas  1049 Jun  1 16:47 
cd8f5f261c82919ebac6ba5dacf77db9.class
-rwxrwxr-x  1 thomas thomas  9345 Jun  1 16:47 
cd8f5f261c82919ebac6ba5dacf77db9.so
-rw-r--r--  1 thomas thomas  2858 Jun  1 16:47 
f0fce2a3b5d05ffa4e5b96ae6718e970.class
-rwxrwxr-x  1 thomas thomas 22675 Jun  1 16:47 
f0fce2a3b5d05ffa4e5b96ae6718e970.so
-rw-r--r--  1 thomas thomas  1261 Jun  1 16:47 
fe125b37d1f3352f478e2244ac81c25.class
-rwxrwxr-x  1 thomas thomas  8991 Jun  1 16:48 
fe125b37d1f3352f478e2244ac81c25.so


-- Thomas