Re: benchmark result

[Mathieu Lacage <Mathieu dot Lacage at sophia dot inria dot fr>]

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. 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);


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
 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



Mathieu
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