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From "Andrew Cornwall" <andrew.pack...@gmail.com>
Subject Re: [classlib][pack200][performance] HashCode optimizations (was: Re: [jira] Updated: (HARMONY-5907) [classlib][pack200]CPUTF8.hashCode() is slow)
Date Mon, 14 Jul 2008 18:38:49 GMT
Sorry - I didn't explain fully. I intended that my code would cache the
Object.hashCode() rather than recomputing the hashCode each time.

On Mon, Jul 14, 2008 at 11:25 AM, Aleksey Shipilev <
aleksey.shipilev@gmail.com> wrote:

> I think that's bad for performance. Using Object.hashCode() leads to
> System.identityHashCode(), which is handled by VM. The exact mechanism
> is VM-dependent, but at least on Harmony it's pretty slow. If you want
> to mark each instance as not-identical to another (warning here, you
> may break something), then I suggest to use static increment, e.g.:
>
> private static int hashcodeBase = 1;
> private int cachedHashCode = hashcodeBase++;
>
> This may end up with cache collisions if objects are created from
> different threads, but that's not the case for now.
>
> Anyway, Andrew, your code lacks caching again ;)
>
> Thanks,
> Aleksey.
>
> On Mon, Jul 14, 2008 at 9:51 PM, Andrew Cornwall
> <andrew.pack200@gmail.com> wrote:
> > And in fact, I just tried the following (which makes even more sense):
> >
> >  - add objectHashCode() to ClassFileEntry:
> >    protected int objectHashCode() {
> >        return super.hashCode();
> >    }
> >
> > - change generateHashCode in ByteCode to return objectHashCode()
> >   private int generateHashCode() {
> >        hashcodeComputed = true;
> >        return objectHashCode();
> >   }
> >
> > Since ByteCodes are equal if and only if they are identical, this seems
> to
> > be the right thing to do. What do you think?
> >
> >
> > On Mon, Jul 14, 2008 at 10:44 AM, Andrew Cornwall <
> andrew.pack200@gmail.com>
> > wrote:
> >
> >> I applied Aleksey's changes, and they look pretty good. I disagree with
> >> Sian to some degree about ByteCode. On my VM (which isn't Harmony), a
> new
> >> empty array's hashCode() is dependent on the array's location in memory,
> and
> >> not the array's contents. In other words:
> >>
> >>         int[] x = new int[3];
> >>         System.out.println(x.hashCode());
> >>         x[1] = 5;
> >>         System.out.println(x.hashCode());
> >>
> >> prints the same value for in both cases. rewrite.hashCode() is a handy
> (if
> >> lazy) way to distinguish among different instances.
> >>
> >> If we take rewrite out of hashCode(), HashMap and HashSet get really
> slow -
> >> essentially a linear search among all the ByteCodes of the same form.
> This
> >> brings my test case from 39 seconds up to 1:02.
> >>
> >> Perhaps the right thing to do is to give each unique instance of
> ByteCode
> >> an integer ID which is used in creating the hashCode rather than relying
> on
> >> rewrite to give us uniqueness?
> >>
> >>
> >> On Mon, Jul 14, 2008 at 7:19 AM, Sian January <
> sianjanuary@googlemail.com>
> >> wrote:
> >>
> >>> Ok - we'll wait and see what Andrew says.  The only one that I'm not
> happy
> >>> with is Bytecode.hashCode, because rewrite always seems to be an empty
> >>> array
> >>> at the point when generateHashCode is called so it's a bit misleading
> >>> using
> >>> it.  I think it should be ok to just remove that line, and still cache
> the
> >>> hashCode.
> >>>
> >>>
> >>> On 14/07/2008, Aleksey Shipilev <aleksey.shipilev@gmail.com> wrote:
> >>> >
> >>> > Sian,
> >>> >
> >>> > Actually I had tried to extend Andrew's approach to these classes
> >>> > first, but somehow I caught the degradation, that leaved me no choice
> >>> > except the lazy initialization. My concern is, the
> >>> > constructor-initialized hashcode is really depend on usage pattern
> for
> >>> > each specific class, while lazy initialization has more guarantees
to
> >>> > be performance-stable. Moreover, I suspect the lazy initialization
> can
> >>> > degrade performance much less because the only overhead it causes is
> >>> > checking the value of boolean field. On the other hand, the
> >>> > constructor initialization may degrade performance a lot since the
> >>> > generation of hashCode is expensive.
> >>> >
> >>> > I can recheck which classes favor lazy initialization and which are
> >>> > not, but I think it's not valuable in terms of efficiency. I mean
> here
> >>> > that the boost connected with changing lazy initialization to
> >>> > constructor one is much lower than boost from caching hashcode
> anyway.
> >>> >
> >>> > Can we accept the patch in this form and revisit this difference
> later?
> >>> > It would be better to focus on more profitable areas for improvements
> >>> for
> >>> > now.
> >>> >
> >>> > P.S. I had asked Andrew to recheck whether my patch works as fast as
> >>> > his, also to check lazy initialization approach. On my tests the
> boost
> >>> > is stable and good.
> >>> >
> >>> > Thanks,
> >>> > Aleksey.
> >>> >
> >>> > On Mon, Jul 14, 2008 at 5:25 PM, Sian January
> >>> > <sianjanuary@googlemail.com> wrote:
> >>> > > Hi Aleksey,
> >>> > >
> >>> > > It's a really good idea to extend this patch to cover some more
> >>> classes,
> >>> > but
> >>> > > I think Andrew's method is faster (a final cachedHashCode field
> that
> >>> is
> >>> > > initialized in the constructor).  The only reason I see to do
it
> later
> >>> > would
> >>> > > be if we thought some of these objects never had hashCode called
on
> >>> them,
> >>> > > but I don't think that's the case.  Would you be able to try that
> >>> method
> >>> > > instead in your patch and see if I'm right about it being faster?
> >>> > >
> >>> > > Thanks,
> >>> > >
> >>> > > Sian
> >>> > >
> >>> > >
> >>> > >
> >>> > > On 12/07/2008, Aleksey Shipilev <aleksey.shipilev@gmail.com>
> wrote:
> >>> > >>
> >>> > >> Andrew,
> >>> > >>
> >>> > >> I had attached the patch to HARMONY-5907, covering several
first
> >>> > >> methods. Can you confirm this patch helps for your scenario?
> >>> > >>
> >>> > >> Thanks,
> >>> > >> Aleksey.
> >>> > >>
> >>> > >> On Sat, Jul 12, 2008 at 1:58 PM, Aleksey Shipilev
> >>> > >> <aleksey.shipilev@gmail.com> wrote:
> >>> > >> > And the sorted list:
> >>> > >> >
> >>> > >> > 95462388         bc.cputf8
> >>> > >> > 18646908         bc.bytecode
> >>> > >> > 15118425         bc.cpclass
> >>> > >> > 14928914         bc.cpnametype
> >>> > >> > 12103799         bc.cpmethref
> >>> > >> > 5159994  bc.cpfieldref
> >>> > >> > 3420605  bc.methref
> >>> > >> > 1840965  bc.cpstring
> >>> > >> > 839916   bc.codeattr
> >>> > >> > 839916   bc.locvarattr
> >>> > >> > 839916   bc.linenumattr
> >>> > >> > 430234   bc.cpmethod
> >>> > >> > 277144   bc.cpfield
> >>> > >> > 263753   bc.attr
> >>> > >> > 153811   bc.cpinteger
> >>> > >> > 121856   bc.newattr
> >>> > >> > 93471    bc.cvalattr
> >>> > >> > 72492    bc.excpattr
> >>> > >> > 57428    bc.srcfileattr
> >>> > >> > 57428    bc.srcfileattr
> >>> > >> > 48104    bc.cplong
> >>> > >> > 40362    bc.innerclass
> >>> > >> > 5593     bc.depattr
> >>> > >> > 3255     bc.cpfloat
> >>> > >> > 1638     bc.cpdouble
> >>> > >> > 532      attrlayout
> >>> > >> > 0       archive
> >>> > >> > 0        attrdef
> >>> > >> > 0        newattrband
> >>> > >> > 0        bc.anndefarg
> >>> > >> > 0        bc.rtannattr
> >>> > >> > 0        classbands
> >>> > >> > 0        filebands
> >>> > >> > 0        metabandgr
> >>> > >> > 0        segheader
> >>> > >> > 0        bc.remattr
> >>> > >> > 0        bc.annattr
> >>> > >> > 0        bc.cpconst
> >>> > >> > 0        bc.cpmember
> >>> > >> > 0        bc.signattr
> >>> > >> > 0        bandset
> >>> > >> > 0        bcbands
> >>> > >> > 0        cpbands
> >>> > >> > 0        icbands
> >>> > >> > 0        ictuple
> >>> > >> > 0        segment
> >>> > >> > 0        segopts
> >>> > >> > 0        bc.classf
> >>> > >> > 0        bc.cpref
> >>> > >> > 0        bc.opmgr
> >>> > >> > 0        bc.rtattr
> >>> > >> > 0        segcp
> >>> > >> > 0        bc.ccp
> >>> > >> > 0        attrlayoutmap
> >>> > >> > 0        bc.encmethattr
> >>> > >> > 0        bc.exptableent
> >>> > >> > 0        bc.locvartable
> >>> > >> > 0        bc.signattr
> >>> > >> >
> >>> > >> > Thanks,
> >>> > >> > Aleksey.
> >>> > >> >
> >>> > >> > On Sat, Jul 12, 2008 at 1:50 PM, Aleksey Shipilev
> >>> > >> > <aleksey.shipilev@gmail.com> wrote:
> >>> > >> >> Hi, Andrew!
> >>> > >> >>
> >>> > >> >> I had updated the internal profiler to support hashCode()
> probes
> >>> [1],
> >>> > >> >> to extend your effort in hashcode optimization. There
are bunch
> of
> >>> > >> >> heavily used hashcodes, most of them are going to
> >>> Object.hashCode()
> >>> > >> >> and then to System.identityHashCode(). We can cache/implement
> >>> > hashcode
> >>> > >> >> for these classes. Here's the profile:
> >>> > >> >>
> >>> > >> >> Hashcodes:
> >>> > >> >>  archive:       0
> >>> > >> >>  attrdef:       0
> >>> > >> >>  attrlayout:    532
> >>> > >> >>  attrlayoutmap: 0
> >>> > >> >>  bandset:       0
> >>> > >> >>  bcbands:       0
> >>> > >> >>  classbands:    0
> >>> > >> >>  cpbands:       0
> >>> > >> >>  filebands:     0
> >>> > >> >>  icbands:       0
> >>> > >> >>  ictuple:       0
> >>> > >> >>  metabandgr:    0
> >>> > >> >>  newattrband:   0
> >>> > >> >>  segcp:         0
> >>> > >> >>  segheader:     0
> >>> > >> >>  segment:       0
> >>> > >> >>  segopts:       0
> >>> > >> >>  bc.attr:        263753
> >>> > >> >>  bc.remattr:     0
> >>> > >> >>  bc.anndefarg:   0
> >>> > >> >>  bc.annattr:     0
> >>> > >> >>  bc.bytecode:    18646908
> >>> > >> >>  bc.ccp:         0
> >>> > >> >>  bc.classf:      0
> >>> > >> >>  bc.codeattr:    839916
> >>> > >> >>  bc.cvalattr:    93471
> >>> > >> >>  bc.cpclass:     15118425
> >>> > >> >>  bc.cpconst:     0
> >>> > >> >>  bc.cpdouble:    1638
> >>> > >> >>  bc.cpfield:     277144
> >>> > >> >>  bc.cpfieldref:  5159994
> >>> > >> >>  bc.cpfloat:     3255
> >>> > >> >>  bc.cpinteger:   153811
> >>> > >> >>  bc.methref:     3420605
> >>> > >> >>  bc.cplong:      48104
> >>> > >> >>  bc.cpmember:    0
> >>> > >> >>  bc.cpmethod:    430234
> >>> > >> >>  bc.cpmethref:   12103799
> >>> > >> >>  bc.cpnametype:  14928914
> >>> > >> >>  bc.cpref:       0
> >>> > >> >>  bc.cpstring:    1840965
> >>> > >> >>  bc.cputf8:      95462388
> >>> > >> >>  bc.depattr:     5593
> >>> > >> >>  bc.encmethattr: 0
> >>> > >> >>  bc.excpattr:    72492
> >>> > >> >>  bc.exptableent: 0
> >>> > >> >>  bc.innerclass:  40362
> >>> > >> >>  bc.linenumattr: 839916
> >>> > >> >>  bc.locvarattr:  839916
> >>> > >> >>  bc.locvartable: 0
> >>> > >> >>  bc.newattr:     121856
> >>> > >> >>  bc.opmgr:       0
> >>> > >> >>  bc.rtattr:      0
> >>> > >> >>  bc.rtannattr:   0
> >>> > >> >>  bc.signattr:    0
> >>> > >> >>  bc.srcfileattr: 57428
> >>> > >> >>
> >>> > >> >> Would you like to produce the patch?
> >>> > >> >> I think it would be funny :)
> >>> > >> >>
> >>> > >> >> Thanks,
> >>> > >> >> Aleksey.
> >>> > >> >>
> >>> > >> >> [1] https://issues.apache.org/jira/browse/HARMONY-5905
> >>> > >> >>
> >>> > >> >> On Sat, Jul 12, 2008 at 12:48 AM, Andrew Cornwall
(JIRA)
> >>> > >> >> <jira@apache.org> wrote:
> >>> > >> >>>
> >>> > >> >>>     [
> >>> > >>
> >>> >
> >>>
> https://issues.apache.org/jira/browse/HARMONY-5907?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
> >>> > ]
> >>> > >> >>>
> >>> > >> >>> Andrew Cornwall updated HARMONY-5907:
> >>> > >> >>> -------------------------------------
> >>> > >> >>>
> >>> > >> >>>    Attachment: main.patch
> >>> > >> >>>
> >>> > >> >>> main.patch includes change to CPUTF8.java
> >>> > >> >>>
> >>> > >> >>>
> >>> > >> >>>> [classlib][pack200]CPUTF8.hashCode() is slow
> >>> > >> >>>> --------------------------------------------
> >>> > >> >>>>
> >>> > >> >>>>                 Key: HARMONY-5907
> >>> > >> >>>>                 URL:
> >>> > >> https://issues.apache.org/jira/browse/HARMONY-5907
> >>> > >> >>>>             Project: Harmony
> >>> > >> >>>>          Issue Type: Improvement
> >>> > >> >>>>    Affects Versions: 5.0M6
> >>> > >> >>>>         Environment: Latest pack200
> >>> > >> >>>>            Reporter: Andrew Cornwall
> >>> > >> >>>>         Attachments: main.patch
> >>> > >> >>>>
> >>> > >> >>>>
> >>> > >> >>>> The unpack process spends a lot of time doing
> CPUTF8.hashCode()
> >>> -
> >>> > >> which does String.hashCode(). We can save about 1.5 seconds
of my
> 39
> >>> > second
> >>> > >> test case (about 4%) by caching the hashCode. (I thought we
did
> this
> >>> > before
> >>> > >> - or maybe I dreamt it?)
> >>> > >> >>>
> >>> > >> >>> --
> >>> > >> >>> This message is automatically generated by JIRA.
> >>> > >> >>> -
> >>> > >> >>> You can reply to this email to add a comment
to the issue
> online.
> >>> > >> >>>
> >>> > >> >>>
> >>> > >> >>
> >>> > >> >
> >>> > >>
> >>> > >
> >>> > >
> >>> > >
> >>> > > --
> >>> > > Unless stated otherwise above:
> >>> > > IBM United Kingdom Limited - Registered in England and Wales with
> >>> number
> >>> > > 741598.
> >>> > > Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire
> PO6
> >>> > 3AU
> >>> > >
> >>> >
> >>>
> >>>
> >>>
> >>> --
> >>> Unless stated otherwise above:
> >>> IBM United Kingdom Limited - Registered in England and Wales with
> number
> >>> 741598.
> >>> Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
> 3AU
> >>>
> >>
> >>
> >
>

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