benchmark result

[Andrew Haley]

Mathieu Lacage writes:
 > On Tue, 2004-12-07 at 10:06 +0000, Andrew Haley wrote:
 > > Mathieu Lacage writes:
 > >  > On Mon, 2004-12-06 at 16:07 +0100, Mathieu Lacage wrote:
 > >  > > On Mon, 2004-12-06 at 13:56 +0000, Andrew Haley wrote:
 > >  > > > We could improve the performance of these collection classes with
 > >  > > > little work.  What is required is someone to study the code, do some
 > >  > > > profiling, and fix things.
 > >  > > 
 > >  > > I will look into this when I find some time.
 > >  > 
 > >  > I tried to replace my iterators by getters on the critical paths of the
 > >  > code. The patch itself is rather simple and I found the results
 > >  > interesting...
 > > 
 > > Could you let me know what you changed?  A diff or somesuch?
 > 
 > It took me a while to find the exact iterator access which triggered the
 > performance gain/loss but this is the 3-liner responsible for 95% of the
 > performance gain you see in my previous email. I believe that this patch
 > has a major influence on the GC too because it avoids the creation of
 > these really short-lived Iterator objects and this code runs in a really
 > tight loop (unexpectedly for me because I had never seen it in any jdk
 > profile). 
 > 
 > In the specific scenario I use here, the m_trees ArrayList always
 > contains only a single element. It seems clear to me that the jdk JIT
 > unrolls this single-iteration loop.

gcj won't unroll at -O2.

 > I already tried to use -fprofile-
 > arcs to avoid this but I get an ICE on gcc 3.4.3 and gcc 4.0.0. I assume
 > this is a known problem.
 > 
 > -               for (Iterator i = m_trees.iterator(); i.hasNext (); ) {
 > -                       Tree tree = (Tree) i.next ();
 > +               int size = m_trees.size ();
 > +               for (int i = 0; i < size; i++) {
 > +                       Tree tree = (Tree) m_trees.get (i);

OK, I see.  I can certainly see why this would be faster for gcj.
This is something we can improve.

 > Here is a new oprofile result:
 > 
 > opreport:
 >     13418 10.2113 libgcj.so.5.0.0
 >      9785  7.4466 MainSimulation
 > 
 > opgprof on libgcj.so:
 >   %   cumulative   self              self     total
 >  time   samples   samples    calls  T1/call  T1/call  name
 >  21.95   2945.00  2945.00                             _ieee754_log

What CPU are you using?  I would expect these calls to log to be
inlined on an x86.

The rest of this looks pretty resonable.  It's still a bit worrying
that we're spending 10% in interface dispatch.

 >  13.09   4701.00  1756.00                             GC_mark_from
 >   9.58   5986.00  1285.00                             Jv_LookupInterfaceMethodIdx
 >   6.60   6871.00   885.00                             ZN4java4util9ArrayList3getEi
 >   5.69   7635.00   764.00                             Z20_Jv_IsAssignableFromPN4java4lang5ClassES2_
 >   5.25   8340.00   705.00                             Jv_CheckCast
 >   4.58   8954.00   614.00                             frame_dummy
 >   3.39   9409.00   455.00                             ZN4java4util14AbstractList$18checkModEv
 >   3.27   9848.00   439.00                             GC_local_gcj_malloc
 >   3.20  10278.00   430.00                             ZN4java4util14AbstractList$17hasNextEv
 >   2.62  10629.00   351.00                             ZN4java4util14AbstractList$14nextEv
 >   2.31  10939.00   310.00                             ZN4java4util9ArrayList19checkBoundExclusiveEi
 >   1.86  11188.00   249.00                             ZN4java4util9ArrayList3addEPNS_4lang6ObjectE
 >   1.42  11379.00   191.00                             Jv_AllocObjectNoFinalizer
 >   1.38  11564.00   185.00                             init
 >   1.33  11742.00   178.00                             Jv_CheckArrayStore
 >   1.26  11911.00   169.00                             ZN4java4util9ArrayList4sizeEv
 >   1.19  12071.00   160.00                             ZN4java4util14AbstractList$16finit$Ev
 >   1.13  12223.00   152.00                             ZN4java4util12AbstractList8iteratorEv
 >   1.04  12362.00   139.00                             ZN4java4lang4Math3logEd
 >   0.95  12490.00   128.00                             log

Andrew.