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From "Nathan Beyer" <ndbe...@apache.org>
Subject Re: [classlib][performance] @Inline and @NoBoundsCheck annotation support
Date Tue, 29 Apr 2008 02:39:43 GMT
On Mon, Apr 28, 2008 at 9:27 PM, Xiao-Feng Li <xiaofeng.li@gmail.com> wrote:

> On Tue, Apr 29, 2008 at 10:11 AM, Nathan Beyer <nbeyer@gmail.com<https://mail.google.com/mail?view=cm&tf=0&to=nbeyer@gmail.com>>
> wrote:
> > On Mon, Apr 28, 2008 at 9:02 PM, Xiao-Feng Li <xiaofeng.li@gmail.com<https://mail.google.com/mail?view=cm&tf=0&to=xiaofeng.li@gmail.com>>
> wrote:
> >
> >
> >  > On Tue, Apr 29, 2008 at 9:13 AM, Nathan Beyer <ndbeyer@apache.org<https://mail.google.com/mail?view=cm&tf=0&to=ndbeyer@apache.org>
> <https://mail.google.com/mail?view=cm&tf=0&to=ndbeyer@apache.org>>
> >  > wrote:
> >  > > What about non-classlib code? If the JIT isn't going to get any
> better
> >  > then
> >  > >  user code is still going to have inline opportunities missed,
> correct?
> >  >
> >  > Right. That's something depending on JIT's capability.
> >  >
> >  > >  This seems like a tactical approach to get faster JRE code in the
> >  > short-term
> >  > >  that won't provide any benefit in the long-term. I'd rather
> advocate
> >  > >  spending egnergy on more strategic concerns.
> >  >
> >  > I agree. The problem is, to improve JIT to cover all the important
> >  > cases is, unfortunately in my estimation, a long and huge effort. And
> >  > JIT has certain limit, which is always not as smart as human being.
> We
> >  > can't expect it can improve in short term. I don't mean JIT will not
> >  > improve. They are two simultaneous efforts. Putting annotation
> doesn't
> >  > exclude any JIT improvement efforts.
> >
> >
> >  So this these annotations would provide something that no other JIT on
> the
> >  market can accomplish?
>
> So far I care mostly about Harmony. If other JIT can do the same thing
> with Harmony classlib, it would be welcome.


But any potential user wouldn't care. Look at it from a consumer's
perspective. A user isn't going to use a Harmony JIT or Harmony Class
Library or a Harmony VM -- they're going to use a Harmony JRE. If another
JRE has a JIT that can perform these optimizations on user code, then
they'll go with that. Regardless of how much inlining and bounds checking
you can remove from class library code, it won't make any difference if you
can't do the same on actual application code.

Don't get me wrong, this sounds like an interesting bit of research. I just
hope it doesn't take away from other efforts. It's interesting, but a better
JIT would be cooler.

-Nathan


>
>
> >  Additionally, these annotations scare me a bit. What if the annotation
> is
> >  wrong? Does the VM just crash in this case?
>
> Valid concern. You can think annotation as part of code. But basically
> it's only a hint, so much less dangerous than wrong code. If wrong
> code can cause VM crash, it is possible for annotation as well.
> Annotation can be completely ignored normally, and only respected when
> aggressive optimizations are desirable.
>

>
> >
> >  >
> >  >
> >  > On the other hand, if Harmony annotations are recognized by the
> >  > community and people start to use them in their application, Harmony
> >  > would gain some benefits. :)
> >
> >
> >  Lets not put the cart before the horse.
>
> Then let's have the horse first. :)
>
> Thanks,
> xiaofeng
>
> >
> >  >
> >  >
> >  > Thanks,
> >  > xiaofeng
> >  >
> >  > >  -Nathan
> >  > >
> >  > >  On Mon, Apr 28, 2008 at 8:03 PM, Xiao-Feng Li <
> xiaofeng.li@gmail.com<https://mail.google.com/mail?view=cm&tf=0&to=xiaofeng.li@gmail.com>
> <https://mail.google.com/mail?view=cm&tf=0&to=xiaofeng.li@gmail.com>>
> >
> >
> > > wrote:
> >  > >
> >  > >  > On Tue, Apr 29, 2008 at 8:03 AM, Nathan Beyer <
> ndbeyer@apache.org<https://mail.google.com/mail?view=cm&tf=0&to=ndbeyer@apache.org>
> <https://mail.google.com/mail?view=cm&tf=0&to=ndbeyer@apache.org>
> >  > <https://mail.google.com/mail?view=cm&tf=0&to=ndbeyer@apache.org>>
> >  > >
> >  > > > wrote:
> >  > >  > > I know I can be silly at times, but why not focus on making
a
> >  > better
> >  > >  > JIT?
> >  > >  >
> >  > >  > Good question... :)  I think the reason is, it's too hard to get
> the
> >  > >  > JIT to do really well all the time. It's not only because the
> JIT is
> >  > >  > not smart enough yet, but also because there are tradeoffs
> between
> >  > >  > compilation time and execution time.
> >  > >  >
> >  > >  > Well, annotation is not the panacea for performance. JIT is
> still the
> >  > >  > major labor. Annotation is likes that when you are climbing on
> crag,
> >  > >  > and accidentally find a dent to put your foot. :)
> >  > >  >
> >  > >  > Thanks,
> >  > >  > xiaofeng
> >  > >  >
> >  > >  > >  -Nathan
> >  > >  > >
> >  > >  > >
> >  > >  > >
> >  > >  > >  On Fri, Apr 25, 2008 at 6:03 AM, Aleksey Shipilev <
> >  > >  > >  aleksey.shipilev@gmail.com<https://mail.google.com/mail?view=cm&tf=0&to=aleksey.shipilev@gmail.com>
> <https://mail.google.com/mail?view=cm&tf=0&to=aleksey.shipilev@gmail.com>
> >  > <
> https://mail.google.com/mail?view=cm&tf=0&to=aleksey.shipilev@gmail.com>>
> >  > >
> >  > >
> >  > > > wrote:
> >  > >  > >
> >  > >  > >  > Hi,
> >  > >  > >  >
> >  > >  > >  > I had returned to idea to have @Inline and @NoBoundCheck
> >  > annotation
> >  > >  > >  > support in classlib and Jitrino.
> >  > >  > >  > I will try to summarize the rationale for both these
> >  > annotations:
> >  > >  > >  >
> >  > >  > >  >  1. @Inline. There are places where we're creating small
> methods
> >  > to
> >  > >  > >  > get more consistent code, while we expect JIT should
inline
> them
> >  > to
> >  > >  > >  > reduce call penalty. Unfortunately, this is not always
the
> case
> >  > and
> >  > >  > >  > any JIT can miss the opportunities for inline. As classlib
> >  > developers
> >  > >  > >  > we can dope our code with the hints saying "this method
is
> >  > really
> >  > >  > >  > should be inlined, as we know it would be the penalty
> leaving it
> >  > not
> >  > >  > >  > inlined, just do it even when inline budget is exhausted".
> >  > Jitrino
> >  > >  > >  > really have @Inline already as the part of vmmagic package,
> but
> >  > I
> >  > >  > want
> >  > >  > >  > to see these annotations visible from the classlib part.
> >  > >  > >  >
> >  > >  > >  > That's the case of new HashMap [1] for example:
> >  > >  > >  >
> >  > >  > >  >    /*
> >  > >  > >  >     * Contract-related functionality
> >  > >  > >  >     */
> >  > >  > >  >    static int computeHashCode(Object key) {
> >  > >  > >  >        return key.hashCode();
> >  > >  > >  >    }
> >  > >  > >  >
> >  > >  > >  >    static boolean areEqualKeys(Object key1, Object key2)
{
> >  > >  > >  >        return key1.equals(key2);
> >  > >  > >  >    }
> >  > >  > >  >
> >  > >  > >  >    static boolean areEqualValues(Object value1, Object
> value2) {
> >  > >  > >  >        return value1.equals(value2);
> >  > >  > >  >    }
> >  > >  > >  >
> >  > >  > >  >
> >  > >  > >  >  2. @NoBoundCheck. There are also cases in which we
> definitely
> >  > know
> >  > >  > >  > that no bound check need to be performed. This is the
case
> of
> >  > HashMap
> >  > >  > >  > again:
> >  > >  > >  >
> >  > >  > >  >    ...
> >  > >  > >  >            int hash = computeHashCode(key);
> >  > >  > >  >            index = hash & (elementData.length -
1);
> >  > >  > >  >            entry = elementData[index];
> >  > >  > >  >    ...
> >  > >  > >  >
> >  > >  > >  >   Of course, good JIT compiler should also resolve such
> patterns
> >  > and
> >  > >  > >  > eliminate bounds check here, but we can again hint the
> compiler
> >  > they
> >  > >  > >  > are not necessary. There's a complication though that
such
> >  > pragma
> >  > >  > >  > could violate security if used in user code, but we
could
> >  > restrict
> >  > >  > its
> >  > >  > >  > usage to bootstrap classes only. ABCD gurus (Egor?)
could
> shed
> >  > more
> >  > >  > >  > light whether it's possible to implement on JIT side.
> >  > >  > >  >
> >  > >  > >  > What do you think? I can elaborate with proof-of-concept
> patches
> >  > to
> >  > >  > >  > see what advantage it would bring.
> >  > >  > >  >
> >  > >  > >  > Thanks,
> >  > >  > >  > Aleksey.
> >  > >  > >  >
> >  > >  > >  > [1] https://issues.apache.org/jira/browse/HARMONY-5791
> >  > >  > >  >
> >  > >  > >
> >  > >  >
> >  > >  >
> >  > >  >
> >  > >  > --
> >  > >  > http://xiao-feng.blogspot.com
> >  > >  >
> >  > >
> >  >
> >  >
> >  >
> >  > --
> >  > http://xiao-feng.blogspot.com
> >  >
> >
>
>
>
> --
> http://xiao-feng.blogspot.com
>

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