Re: performance regression with trunk's gengtype on ARM?

[Mikael Pettersson <mikpe at it dot uu dot se>]

Mikael Pettersson writes:
 > Mikael Pettersson writes:
 >  > I'm seeing what appears to be a recent massive performance regression
 >  > with trunk's gengtype, as compiled and run in stage 2, on ARM V5TE.
 >  > 
 >  > Right now 4.7-20110827's stage2 gengtype has been running for almost
 >  > 10 hours on my ARM build machine, but the process is tiny and no swapping
 >  > occurs.  To put those 10 hours in perspective, on this machine (1.6 GHz
 >  > ARM V5TE uniprocessor running Linux) I regularly do full bootstraps and
 >  > regression test suite runs for c,c++,ada,fortran in about 18 hours for
 >  > gcc 4.4, about 20 hours for gcc 4.5, about 24 hours for gcc 4.6, and
 >  > about 27 hours for trunk until recently.  So 10 hours or more just in
 >  > stage 2 gengtype is suspicious.
 >  > 
 >  > I believe 4.7-20110820 also was unusually slow to build, but I didn't
 >  > monitor that build very carefully so can't say if gengtype was involved
 >  > then too.
 > 
 > It's now been running for almost 21 hours, with no output produced at all.
 > According to strace it's currently not doing any syscalls, and according
 > to gdb it's looping in yylex().  I suspect a miscompilation.
 > 
 > Anyway I'm killing that build now.  I have a pile of stable branch
 > backports to test, after that I might try a regression hunt on trunk.

The regression

a) was repeatable, and
b) got fixed in 4.7-20110903.

I'm not going to investigate this any further, unless I'm forced
to do a regression hunt in this date range in the future.