[EXT] Follow-up results for SwissTable with Vector API

[Paul Sandoz]

In some further replies I just noticed you dropped the panama-dev email. Resend a summary of the discussion?

Paul.

> On Jan 5, 2023, at 2:16 PM, Zhu, Yifan <yzhu104 at UR.Rochester.edu> wrote:
> 
> I am confused. It seems that my replies are detached from the mailling list. It that expected?
> 
> 
> <Outlook-3cjuahvq.png>
> Schrodinger ZHU Yifan, Ph.D. Student
> Computer Science Department, University of Rochester
> 
> Personal Email: i at zhuyi.fan
> Work Email: yifanzhu at rochester.edu
> Website: https://www.cs.rochester.edu/~yzhu104/Main.html
> Github: SchrodingerZhu
> GPG Fingerprint: BA02CBEB8CB5D8181E9368304D2CC545A78DBCC3
> 
> <Outlook-fjqcbbcv.svg>
> 发件人: panama-dev <panama-dev-retn at openjdk.org> 代表 Paul Sandoz <paul.sandoz at oracle.com>
> 发送时间: 2023年1月6日 0:29
> 收件人: Zhu, Yifan <yzhu104 at UR.Rochester.edu>
> 抄送: panama-dev at openjdk.org <panama-dev at openjdk.org>
> 主题: [EXT] Re: Follow-up results for SwissTable with Vector API
>  
> Hi,
> 
> I saw you sent another email prior to this, but for some reason it got lost by the moderation system. (Since you are not a member of the list the emails need to be moderated and approved.)
>  
> 
> > On Jan 5, 2023, at 8:09 AM, Zhu, Yifan <yzhu104 at UR.Rochester.edu> wrote:
> > 
> > This is the following up message for https://urldefense.com/v3/__https://mail.openjdk.org/pipermail/jdk-dev/2023-January/007288.html__;!!CGUSO5OYRnA7CQ!c6-WVSHfkvXgbKEtNWhxgdZ9EHDDMbmUz9AbxpvbYN54xt_4LzTwYJd4PdHmueDBCmryWsWBXfjE-Jpw_Cfrf6WyAw$ .
> > 
> > > You do:
> > >  converted.intoMemorySegment(MemorySegment.ofArray(control), offset, ByteOrder.nativeOrder());
> > >
> > > Can you just do: 
> > >
> > >  converted.intoArray(control, offset);
> > 
> > 
> > I did so because I found that Vector<Byte> actually does not have that method.
> 
> Ah, yes. There could be an perf issue with memory segment access, although since you had to wrap the array in a segment there will be some cost to that. It’s like if you wrapped the control array in a segment and stored in a field it would work better. 
> 
> 
> > After your suggestion, I switched to use ByteVector instead by Vector<Byte>. Surprisingly, this time the hashmap delivers a better performance. It 2~3 times faster during the insertion procedure. 
> 
> Good!
> 
> 
> > However, there was still a performance gap behind the standard hashmap during finding precedure.
> > 
> > For the ease of discussion, I attach the relevant code here:
> > 
> > private int findWithHash(long hash, K key) {
> >     byte h2 = Util.h2(hash); //highest 7 bits
> >     int position = Util.h1(hash) & bucketMask; // h1 is just long to int
> >     int stride = 0;
> >     while (true) {
> >         var mask = matchByte(position, h2).toLong(); // match byte is to load a vector of byte and do equality comparison
> >         while (MaskIterator.hasNext(mask)) { 
> >             var bit = MaskIterator.getNext(mask);
> >             mask = MaskIterator.moveNext(mask);
> >             var index = (position + bit) & bucketMask;
> >             if (key.equals(keys[index])) return index;
> >         }
> > 
> >         if (matchEmpty(position).anyTrue()) {
> >             return -1;
> >         }
> > 
> >         stride += VECTOR_LENGTH;
> >         position = (position + stride) & bucketMask;
> >     }
> > }
> > From Intellij IDEA's profiler, it seems that a large portion of time is spent on building the vectormask. I see there is an underlying bTest operation converting the results to boolean array and then give the mask. Will this be internally optimized to a single movemask operation by JVM?
> > 
> 
> Can you get an inline/compilation trace like you did for insert?
> 
> The VectorMask.toLong method is an intrinsic method.
> 
> Try:
> 
>   var vmask = matchByte(position, h2);
>   var mask = mask.toLong();
> 
> Probably will not make any difference, but if the findIInsertSlot performed ok operating on the mask returned from matchEmptyOrDelete it points to an issue with VectorMask.toLong.
> 
> Paul.
>  
> > 
> > <Outlook-ejiaczyb.png>
> > Schrodinger ZHU Yifan, Ph.D. Student
> > Computer Science Department, University of Rochester
> > 
> > Personal Email: i at zhuyi.fan
> > Work Email: yifanzhu at rochester.edu
> > Website: https://www.cs.rochester.edu/~yzhu104/Main.html
> > Github: SchrodingerZhu
> > GPG Fingerprint: BA02CBEB8CB5D8181E9368304D2CC545A78DBCC3
> > 
> > <Outlook-3nrq0klq.svg>
>