Help requested: Interpreting results from bench.pl

Hi all,

I've been trying to measure performance of a set of changes on a
branch. To do this I've arranged to run Porting/bench.pl at several
stages along the branch, so I can compare a bunch of numbers between
the runs. What I end up with looks like this:

AVERAGE

        blead      p1    p1+1     p1+4    p1+5     p1+6    p1+7     p1+8
       ------ ------- ------- -------- ------- -------- ------- --------
    Ir 100.00   99.98   99.98    99.98   99.98    99.98   99.98    99.98
    Dr 100.00   99.98   99.98    99.98   99.98    99.98   99.98    99.98
    Dw 100.00   99.99   99.99    99.99   99.99    99.99   99.99    99.99
  COND 100.00   99.97   99.97    99.97   99.97    99.97   99.97    99.97
   IND 100.00  100.00  100.00   100.00  100.00   100.00  100.00   100.00

COND_m 100.00  112.64  102.73    96.57   84.61   107.92  113.36   113.77
 IND_m 100.00  100.00   99.24    99.24  100.00   100.00  100.00    99.99

 Ir_m1 100.00   66.28   96.14    91.83   47.18    66.57   66.12    54.55
 Dr_m1 100.00  100.26  100.29   100.13  100.16   100.34  100.27   100.24
 Dw_m1 100.00   99.40   99.40    99.40   99.40    99.20   99.80    99.80

 Ir_mm 100.00  100.00  100.00   100.00  100.00   100.00  100.00   100.00
 Dr_mm 100.00  100.00  100.00   100.00  100.00   100.00  100.00   100.00
 Dw_mm 100.00  100.00  100.00   100.00  100.00   100.00  100.00   100.00

(ignore the missing +2 and +3; I deleted those columns having
determined that those changes make no difference at all to the numbers
here).

I get that "bigger numbers are faster", so I can see that various of
these commits in some sense make the perl "slower", and occasional
spikes above 100 that might apparently make some things faster.

But beyond that I don't really have a feel for how to interpret all of
this. For instance, the commits between +4 and +5 have made the Ir_m1
score drop from 91.83 all the way down to 47.18 - what does that
actually mean? If I want to look in more detail into the code and try
to work out what specifically slowed it down and how to improve it so
it isn't as bad, what should I be looking for?

-- 
Paul "LeoNerd" Evans

[email protected]
http://www.leonerd.org.uk/  |  https://metacpan.org/author/PEVANS