2009 Update

[Peter Chubb]

>>>>> "C" == C Bergström <codestr0m at osunix.org> writes:

C> Peter Chubb wrote:
>>>>>>> "Anton" == Anton Shterenlikht <mexas at bristol.ac.uk> writes:
>>>>>>> 
>>
Anton> On Sat, Nov 07, 2009 at 05:26:27PM -0500, "C. Bergström" wrote:
>>
Anton> There are 6 ia64 systems on top500 list (details below). All
Anton> run linux, of course. But these organisations must use very
Anton> good compilers, and, at least for nuclear codes (systems 71 and
Anton> 96), these will be f90-f95 or even f2003 (I don't know of any
Anton> f2008) compilers. Perhaps they do use PathScale and forget
Anton> about GCC..
>> Most use the Intel compiler, and heavy hand-optimization of inner
>> loops using tools like vTune.
>> 
>> Gelato put a lot of effort into imprving gcc for IA64 -- gcc 4.x is
>> miles better than gcc 3.x -- but there's still a lot that could be
>> done with low-level instruction scheduling.
>> 
>> 
C> I do not normally discourage people to work on other compilers, but
C> working on GCC for IA64 is a complete waste of time.  With that I
C> do agree the current situation for IA64 is less than ideal.. I'm
C> happy to hear complaints and do what is within my resources and
C> capability to fix..


The reason we put so much effort into attempting to improve things is
that most people will just try to run their code with the compiler(s)
they already know.  And the code generated by gcc was appalling, so
Itanium appeared to suck badly.  Fixing GCC meant that users could
continue to use the toolchains they already knew, and maybe they'd get
halfway decent results.    The stuff we did is documented at
http://gcc.gelato.org/



People can still do better, by using the Intel compiler, but even it
was non-optimal for system code (although I haven't tried it recently:
it may have improved), and needed (again, I haven't looked recently,
this may be out of date) careful tuning to get good performance for
enterprise workloads.

--
Dr Peter Chubb		www.nicta.com.au    peter DOT chubb AT nicta.com.au
http://www.ertos.nicta.com.au           ERTOS within National ICT Australia