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From "Aleksey Shipilev" <aleksey.shipi...@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 21:08:41 GMT
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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