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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 Fri, 18 Jul 2008 22:49:01 GMT
Just to come back to this: I tried replacing Object.hashCode() with a static
counter. The performance was significantly worse: >5 minutes instead of 34
seconds using my test case, even when using a large prime as the counter
increment rather than a smaller number.

On Mon, Jul 14, 2008 at 2:08 PM, Aleksey Shipilev <
aleksey.shipilev@gmail.com> wrote:

> That's the question worth experimenting.
> But taking into consideration that hashcode will not be generated
> frequently, Object.hashCode() seem to be well too.
>
> On Tue, Jul 15, 2008 at 12:37 AM, Andrew Cornwall
> <andrew.pack200@gmail.com> wrote:
> > I think Object.hashCode() will be better distributed than a static
> increment
> > - wouldn't that have better performance in Hash* objects?
> >
> >
> > On Mon, Jul 14, 2008 at 11:44 AM, Aleksey Shipilev <
> > aleksey.shipilev@gmail.com> wrote:
> >
> >> Nevertheless, Object.hashCode() performance is unclear and as such it
> >> should be specifically avoided if not required explicitly. Will static
> >> increment suit better?
> >>
> >> Thanks,
> >> Aleksey.
> >>
> >> On Mon, Jul 14, 2008 at 10:38 PM, Andrew Cornwall
> >> <andrew.pack200@gmail.com> wrote:
> >> > 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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