Improving the performance of OpenJDK

[Gary Benson]

Gary Benson wrote:
> Andrew Haley wrote:
> > Gary Benson wrote:
> > > Edward Nevill wrote:
> > > > get_native_u2() and get_Java_u2() ... This seems to be a
> > > > misguided attempt of the original authors to optimised reading
> > > > of halfwords (judging by the comment immediate preceding the
> > > > code).
> > > 
> > > It's not an optimization, it's to do unaligned access on
> > > hardware that doesn't support it.  I'm guessing ARM does allow
> > > unaligned access by the fact that your code didn't segfault
> > > instantly ;)
> > 
> > ARM doesn't support unaligned loads.  The new ARM code as posted
> > is
> > 
> > 	ldrsb	r0, [java_pc, #0]
> > 	ldrb	r1, [java_pc, #1]
> > 	orr	r1, r1, r0, lsl #8
> > 
> > i.e two byte loads.
> 
> Ah, I didn't realise.  Which is good, it means this optimization is
> generic :)

So I did a quick SPECjvm98 run of this change on amd64.  A couple of
the times are improved, by 3-10%, but one of the times is *slower*
by 11%.  See attached.  I'm not sure what to make of that...

Cheers,
Gary

-- 
http://gbenson.net/
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,times/zero-92c4cc753f06,times/zero-92c4cc753f06-u2
compress,231.02,255.489
jess,70.363,64.099
db,116.143,112.242
javac,72.624,69.744
mpegaudio,229.505,226.654
mtrt,59.302,59.274
jack,49.195,44.505
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