Drop GCJ AOT bits for F11?

11-20-2008, 03:33 PM

Andrew Overholt wrote:

> Back when we wrote the initial Java packaging guidelines, we said that
> packagers *should* include GCJ AOT bits. Should we remove this
> requirement for Fedora 11 and beyond?
>
> Also, GCJ is still in the base install set for Fedora. Should we remove
> this and make OpenJDK a default?

This is a bit premature. We still don't have the OpenJDK JIT for PPC and
ARM arches. We're working hard on it but it's not ready yet for prime-time.
Without the JIT, OpenJDK is crushingly slow on these arches.

Having said that, there's no reason not to make OpenJDK the default on the
arches where it performs well: x86 and 8x6_64 at the monent.

Andrew.

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11-20-2008, 03:43 PM

* Andrew Haley <aph@redhat.com> [2008-11-20 11:33]:
> Andrew Overholt wrote:
>
> > Back when we wrote the initial Java packaging guidelines, we said that
> > packagers *should* include GCJ AOT bits. Should we remove this
> > requirement for Fedora 11 and beyond?
> >
> > [...]
>
> This is a bit premature. We still don't have the OpenJDK JIT for PPC and
> ARM arches. We're working hard on it but it's not ready yet for prime-time.
> Without the JIT, OpenJDK is crushingly slow on these arches.

Should Smolt stats on architecture users affect this decision? It says
about 0.7% of users are on platforms without OpenJDK JITs.

http://smolts.org/static/stats/stats.html

Andrew

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11-20-2008, 04:00 PM

Andrew Overholt wrote:
> * Andrew Haley <aph@redhat.com> [2008-11-20 11:33]:
>> Andrew Overholt wrote:
>>
>>> Back when we wrote the initial Java packaging guidelines, we said that
>>> packagers *should* include GCJ AOT bits. Should we remove this
>>> requirement for Fedora 11 and beyond?
>>>
>>> Also, GCJ is still in the base install set for Fedora. Should we remove
>>> this and make OpenJDK a default?
>>
>> This is a bit premature. We still don't have the OpenJDK JIT for PPC and
>> ARM arches. We're working hard on it but it's not ready yet for prime-time.
>> Without the JIT, OpenJDK is crushingly slow on these arches.
>
> Should Smolt stats on architecture users affect this decision? It says
> about 0.7% of users are on platforms without OpenJDK JITs.
>
> http://smolts.org/static/stats/stats.html

I was hoping to be able to keep all arches going with gcj until a
really first-rate OpenJDK solution was available everywhere. I don't
think we want to make the useers of these arches into second- class
citizens: Fedora ARM, in particular, is great for mobile devices and
hasn't been supported for very long. I think its usage will increase.

Sure, the number of users is low, but on lower-performance boxes the
penalty of not having gcj and gcj-compiled packages available is quite
severe. I wouldn't object to weakening the "should" to a "may" where
aot-compiling is a problem. Even without precompiled applications,
gcj is still a lot faster than the OpenJDK C++ interpreter.

Andrew.

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11-20-2008, 04:09 PM

On Thursday 20 November 2008 09:00:50 am Andrew Haley wrote:
> Andrew Overholt wrote:
> > * Andrew Haley <aph@redhat.com> [2008-11-20 11:33]:
> >> Andrew Overholt wrote:
> >>> Back when we wrote the initial Java packaging guidelines, we said that
> >>> packagers *should* include GCJ AOT bits. Should we remove this
> >>> requirement for Fedora 11 and beyond?
> >>>
> >>> Also, GCJ is still in the base install set for Fedora. Should we
> >>> remove this and make OpenJDK a default?
> >>
> >> This is a bit premature. We still don't have the OpenJDK JIT for PPC
> >> and ARM arches. We're working hard on it but it's not ready yet for
> >> prime-time. Without the JIT, OpenJDK is crushingly slow on these arches.
> >
> > Should Smolt stats on architecture users affect this decision? It says
> > about 0.7% of users are on platforms without OpenJDK JITs.
> >
> > http://smolts.org/static/stats/stats.html
>
> I was hoping to be able to keep all arches going with gcj until a
> really first-rate OpenJDK solution was available everywhere. I don't
> think we want to make the useers of these arches into second- class
> citizens: Fedora ARM, in particular, is great for mobile devices and
> hasn't been supported for very long. I think its usage will increase.
>
> Sure, the number of users is low, but on lower-performance boxes the
> penalty of not having gcj and gcj-compiled packages available is quite
> severe. I wouldn't object to weakening the "should" to a "may" where
> aot-compiling is a problem. Even without precompiled applications,
> gcj is still a lot faster than the OpenJDK C++ interpreter.
>
> Andrew.

I'm also for keeping gcj (for now). OpenJDK is great where it JITs but it's
miserable on PPC (e.g. my laptop). I think the guidelines could say something
about "if you run into a problem with a non trivial fix compiling gcj AOT
bits, it's ok to drop the aot bits".

Regards,
--
Conrad Meyer <konrad@tylerc.org>

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11-20-2008, 06:49 PM

* Andrew Haley <aph@redhat.com> [2008-11-20 12:00]:
> I was hoping to be able to keep all arches going with gcj until a
> really first-rate OpenJDK solution was available everywhere.

Do we anticipate this happening before the F11 freeze? When I asked
this question it wasn't meant as a "let's do it today!" kind of thing
but more a "we need to seriously think about this for F11 now that F10
is basically out the door"

.

> Sure, the number of users is low, but on lower-performance boxes the
> penalty of not having gcj and gcj-compiled packages available is quite
> severe.

Do we have numbers on this? I know you are correct but having hard
numbers would be nice.

Andrew

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11-21-2008, 12:36 PM

On Thu, 2008-11-20 at 14:49 -0500, Andrew Overholt wrote:
> * Andrew Haley <aph@redhat.com> [2008-11-20 12:00]:
> > Sure, the number of users is low, but on lower-performance boxes the
> > penalty of not having gcj and gcj-compiled packages available is quite
> > severe.
>
> Do we have numbers on this? I know you are correct but having hard
> numbers would be nice.

I only have anecdotal evidence (I did these experiments a long time
ago). Running eclipse fully interpreted, through for example jamvm
(sadly not packaged for Fedora yet), is on the order of 4 to 8 times as
slow as running eclipse interpreted with gij and aot-compiled core class
libraries. And the jamvm interpreter is faster than the standard
interpreter that comes with hotspot.

Comparing gij on a pure-bytecode program versus a the same compiled aot
with gcj doesn't directly give you the correct (hard) numbers though.
Since gij will at least use the aot compiled core-library (so at least
things like your String operations and HashMaps, etc are optimized).

I believe Andrew Hughes (CCed) has a zero-on-x86 install. So he might be
able to give a real number of how much slower zero-interpreted against
full hotspot and/or a fully gcj native compiled program is.

Cheers,

Mark

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