gcj jit, timing comparison

Thu Jun 1 19:59:00 GMT 2006

On 1-Jun-06, at 11:12 AM, Thomas Johnsson wrote:
> 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?

The BC-ABI (-findirect-dispatch) is used by the gcj-jit and carries 
some overhead, as does shared library (-fPIC) code. Possibly, the way 
that gcj-jit loads a large number of small shared libraries 
introduces overheads as well - a large number of GC static roots, etc.
Bryce